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Cell phone use is among the most prevalent types of in-vehicle distractions. Studies have shown cell phones to have a negative impact on driving performance, with the magnitude of these impacts varying based on the level of engagement required for phone use, as well as the complexity of the driving environment. The development of effective policies and programs to mitigate distracted driving is contingent on an improved understanding of the nature of these relationships. To this end, this study investigates the rate of cell phone use under various settings through a statewide direct observation survey. Data were collected from 200 roadside locations throughout the State of Michigan and a random effects multinomial logit model was estimated to assess how the prevalence of cell phone use varies across drivers. While several studies have investigated the prevalence of cell phone use, this study distinguishes differences in the manner of cell phone use (i.e., talking on a handheld device versus manual manipulation of the device) across drivers while controlling for important contextual factors. The results show cell phone use is generally higher among female drivers and use rates consistently decrease with age. The prevalence of cell phone use is also shown to vary significantly depending on the manner of use. Use rates are shown to differ based on changes in the driving environment, suggesting potential risk compensation on the part of motorists. The results also show a significant correlation in use rates at the same sites over time, which is reflective of important unobserved site-specific factors.

Access control remains an important concern to roadway agencies as the spacing of at-grade access points significantly affects both the safety and operational performance of highways. Significant variability exists with respect to policies dictating where the first access points may occur in the vicinity of interchanges. This study examines two important spacing criteria, which include: (1) the distance from the freeway off-ramp to the first access on the interchanging arterial roadway; and (2) the distance from a freeway on-ramp to the first at-grade intersection in areas with partial access control. To investigate these relationships, a series of crash prediction models were estimated that examined how crash risk changed with respect to access spacing while controlling for the effects of traffic volume and other pertinent characteristics. The results illustrate that at cross-streets near ramp terminal intersections, the crash rate generally increases as the distance to the nearest access point decreases. The same trend was also true of freeway transition areas. Ultimately, this research illustrates a complex relationship that exists among the proximity of the exit point of the controlled access facility and the adjacent access point, the volume of traffic along the roadway, and the volume of traffic at the access point.

Safety performance functions (SPFs) were developed for rural two-lane county roadway segments in Michigan. Five years of crash data (2011 to 2015) were analyzed for greater than 6,500 mi of rural county roadways, covering 29 of Michigan’s 83 counties and representing all regions of the state. Three separate models were developed to estimate annual deer-excluded total and injury crashes on rural county roadways: 1) paved federal-aid segments, 2) paved non-federal-aid segments, and 3) paved and gravel non-federal-aid segments with fewer than 400 vpd. To account for the unobserved heterogeneity associated with differing county design standards, mixed effects negative binomial models with a county-specific random effect were utilized. Not surprisingly, the county segment SPFs generally differed from traditional models generated using data from state-maintained roadways. County federal-aid roadways general showed greater crash occurrence than county non-federal-aid roadways, the Highway Safety Manual (HSM) two-lane rural roadways model, and rural state highways in Michigan. County non-federal-aid paved roadways showed crash occurrence rates that were remarkably similar to the HSM base rural two-lane roadway model, whereas gravel roadways showed greater crash occurrence rates. The presence of horizontal curves with design speeds below 55 mph had a strong association with the occurrence of total and injury crashes across all county road classes. Increasing driveway density was also found to be associated with increased crash occurrence. However, lane width, roadway surface width, and paved shoulder width had little to no impact on total or injury crashes.

Introduction Prior research has shown the probability of a crash occurring on horizontal curves to be significantly higher than on similar tangent segments, and a disproportionally higher number of curve-related crashes occurred in rural areas. Challenges arise when analyzing the safety of horizontal curves due to imprecision in integrating information as to the temporal and spatial characteristics of each crash with specific curves. Methods The second Strategic Highway Research Program(SHRP 2) conducted a large-scale naturalistic driving study (NDS),which provides a unique opportunity to better understand the contributing factors leading to crash or near-crash events. This study utilizes high-resolution behavioral data from the NDS to identify factors associated with 108 safety critical events (i.e., crashes or near-crashes) on rural two-lane curves. A case-control approach is utilized wherein these events are compared to 216 normal, baseline-driving events. The variables examined in this study include driver demographic characteristics, details of the traffic environment and roadway geometry, as well as driver behaviors such as in-vehicle distractions. Results Logistic regression models are estimated to discern those factors affecting the likelihood of a driver being crash-involved. These factors include high-risk behaviors, such as speeding and visual distractions, as well as curve design elements and other roadway characteristics such as pavement surface conditions. Conclusions This paper successfully integrated driver behavior, vehicle characteristics, and roadway environments into the same model. Logistic regression model was found to be an effective way to investigate crash risks using naturalistic driving data. Practical Applications This paper revealed a number of contributing factors to crashes on rural two-lane curves, which has important implications in traffic safety policy and curve geometry design. This paper also discussed limitations and lessons learned from working with the SHRP 2 NDS data. It will benefit future researchers who work with similar type of data.

The flipped-classroom approach has gained increasing popularity and interest in engineering education. The purpose of this study was to investigate (a) student perspectives on the flipped-classroom approach in a transportation-engineering course and (b) how students used the in-class time dedicated to collaborative problem solving. To this end, the study adopted a mixed-methods approach. Quantitative data included an end-of-semester survey and student course grades. Qualitative data included information from focus-group interviews with students and video recordings that demonstrated selected groups’ problem-solving processes. The results indicated that students found their flipped-classroom experience to be generally positive. Students were shown to engage in five types of behaviors during collaborative problem solving: problem analysis or understanding, individually working on problems, comparing individual work, interacting with peers, and interacting with the instructor.

Work zone temporary traffic control strategies generally affect both traffic safety and operations. However, there is a substantial gap in the knowledge base with respect to the safety impacts of various work zone characteristics. The Highway Safety Manual provides crash modification functions that account for the effects of project length and duration on crash frequency as compared with normal road operations. However, these methods do not allow for explicit comparisons of expected safety performance among different work or closure types. This research examined the safety impacts of various temporary traffic control strategies on freeways, including shoulder closures, lane closures, and lane shifts. Data were collected for the periods during which these treatments were in effect and during similar nonconstruction periods from the preceding year. Safety performance functions were estimated that account for segment length, duration, traffic volume, and closure type. Random parameter count data models were estimated to accommodate segment-specific temporal correlation and unobserved heterogeneity. Crash rates were shown to vary roughly in proportion to traffic volumes. In contrast, segment length and project duration showed inelastic effects; this finding implies that crash rates increase more rapidly in work zones that are shorter in length or duration. Single-lane closures, multilane closures, and lane shifts were associated with an increase in crashes, whereas shoulder closures did not show a significant difference compared with similar, non-work-zone conditions. Ultimately, the study results provide important information that can be used to assess the crash risk for various temporary traffic control strategies.

Speed limits on rural highways have recently been on an upward trend nationwide as 25 states have increased speed limits on such roadways between 2011 and 2016. In January 2017, Michigan House Bill 4423 (Public Act 445) was signed into law, which required speed limits to be raised from 55 to 65 mph on at least 900 mi of Michigan’s state-maintained nonfreeways. The specific highway segments were to be selected by the Michigan Department of Transportation (DOT) within 1 year of enactment on the basis of an assessment of travel speeds and safety. Research was undertaken to develop a process to select candidate highway segments for speed limit increases in Michigan. The primary objective was to identify rural highway segments with comparatively low safety risks for which costly geometric upgrades, specifically horizontal or vertical realignment, would be avoided. Ultimately, 12 factors and associated selection criteria were used to identify the candidate segments. These factors included segment length, total crash rate, injury crash rate, severe (fatal and A-injuries) crash rate, horizontal curvature, speed reduction zones, no-passing zones, schools (kindergarten through eighth grade), driveway density, lane width, paved shoulder width, and signalized intersections. Application of the candidate selection criteria to the Michigan DOT nonfreeway network yielded 772.8 centerline miles along 33 candidate segments, which represented approximately one-eighth of the network mileage currently posted at 55 mph. To avoid substantial geometric upgrade costs, speed limit increases were specifically not recommended for segments that would require horizontal or vertical realignment to achieve design speed compliance with the increased speed limit.

As of November 2016, Montana was the only state to maintain a differential speed limit on two-lane two-way rural highways, with a daytime statutory speed limit of 70 mph for cars and light trucks and 60 mph for trucks exceeding a 1-ton payload capacity. Although differential speed limits are common on freeways, the use of differential limits on two-lane roadways presents unique safety and operational issues because of passing limitations and the resultant platooning that occurs. Given these concerns, the speed limit was changed from the differential 70 mph to 60 mph speed limit to a uniform 65 mph limit for all vehicles along 55 mi of two-lane highway in April 2013. This study evaluated the short-term operational and safety impacts associated with this transition. Given the limited time period over which data were available following the speed limit change, surrogate safety measures were investigated to provide immediate feedback as to these impacts. A series of field studies was performed on two-lane rural highways in Montana, which predominantly possessed the 70 mph to 60 mph differential speed limit, as well as on selected locations along the 55 mi where the uniform speed limit was implemented. The locations with 65 mph speed limits generally exhibited shorter platoon lengths and less high-risk passing behavior. Overall, the preliminary findings provide some general support for transitioning to a uniform 65 mph speed limit on two-lane rural highways.

Intersections experience a disproportionate share of traffic crashes, injuries, and fatalities because of the increased number of conflicting traffic movements at these locations. These issues are particularly pronounced at rural locations where speeds are generally higher and most intersections are either stop- or yield-controlled. Ideally, intersecting roadways should be oriented at as close to a 90-degree angle as possible. However, intersection design can diverge from this preferred configuration and result in a skewed intersection. Skewed intersections have been found to cause safety and operational issues for road users. To determine the effect of intersection skewness on crash frequency, crash prediction models were estimated for rural stop-controlled intersections on high-speed two-lane highways throughout the state of Iowa. Separate analyses were conducted for three-leg and four-leg intersections. In both cases, crash frequency was estimated as a function of annual average daily traffic, skew angle, and other salient geometric characteristics. The results consistently showed crash frequency to increase with skew angle. A 10-degree deviation from 90 degrees would result in 3% more crashes at three-leg intersections and 4% more crashes at four-leg intersections. In addition, crashes were affected by the volume of heavy vehicles, whether the approaches were paved or unpaved and whether intersection lighting was present.

Field studies were performed to compare the effectiveness of traffic control countermeasures commonly used at uncontrolled midblock crosswalks. Various crosswalk treatments were evaluated at 31 low-speed midblock crosswalks located near three public universities. The study locations included unmarked crosswalks, in addition to standard and continental crosswalk markings, some including an additional enhancement device such as the pedestrian hybrid beacon (PHB), rectangular rapid flashing beacon (RRFB), or an in-street R1–6 sign. Driver yielding compliance during staged pedestrian crossing events was used as the measure of effectiveness. To isolate the crosswalk treatment effects, several roadway and traffic characteristics were included in the analysis, including the crossing distance, median presence, vehicular and pedestrian volumes, travel lane of the subject vehicle, and the subject vehicle’s position in a queue. A mixed effects logistic regression model was used to account for correlation in yielding rates within the same sites as well as for unobserved heterogeneity across locations. The results indicate that the type of crosswalk treatment has a strong influence over driver yielding compliance. While yielding compliance improved substantially when crosswalk markings were used, the highest compliance rates were achieved when an additional enhancement device (i.e., RRFB, PHB, or R1–6 sign) was also provided. Yielding compliance showed little sensitivity to the particular travel lane of the subject vehicle at locations where a crosswalk enhancement device was used, further validating the effectiveness of these treatments. Finally, yielding compliance rates were generally higher across each of the crosswalk enhancement devices compared with prior studies performed in the same areas, suggesting compliance improves as drivers become more familiar with these devices.

In recent years, there have been a series of innovations in the field of vehicle detection at intersection approaches. Modern radar-based smart sensors make it possible to track individual vehicles in close proximity to an intersection. These advancements in technology potentially enable the provision of vehicle- and site-specific decision dilemma zone protection at the onset of the yellow indication at signalized intersections. To exploit this opportunity, it is critical to develop an in-depth understanding of those factors influencing a driver's decision to stop or go at the onset of yellow. This study investigates how signal timing strategies such as yellow interval durations, all-red clearance intervals, advance warning flashers, and automated camera enforcement affect driver decision-making. Data from 87 intersection approaches across five regions of the United States are used to develop a series of decision (i.e., probability of stopping) curves using vehicle trajectory and signal phasing data. A panel data random parameters probit model is used to account for heterogeneity across locations, as well as correlation in driver decision-making, due to unobserved factors that are unique to each signalized intersection. The results demonstrate drivers are more likely to stop at locations where enforcement cameras or flashers are present. Stopping was also more prevalent at intersections with lower speed limits, longer crossing distances, and where pedestrian crosswalks were present.

Motorcycle riders account for a disproportionately high number of traffic injuries and fatalities compared to occupants of other vehicle types. Though research has demonstrated the benefits of helmet use in preventing serious and fatal injuries in the event of a crash, helmet use has remained relatively stable in the United States, where the most recent national estimates show a 64% use rate. Use rates have been markedly lower among those states that do not have a universal helmet law for all riders. In 2012, the state of Michigan repealed its longstanding mandatory helmet use law. In order to gain insights as to the effects of this legislative change, a study was conducted to examine short-term changes in helmet use and identify factors associated with use rates.A statewide direct observation survey was conducted 1 year after the transition from a universal helmet law to a partial helmet law. A random parameters logistic regression model was estimated to identify motorcyclist, roadway, and environmental characteristics associated with helmet use. This modeling framework accounts for both intravehicle correlation (between riders and passengers on the same motorcycle) as well as unobserved heterogeneity across riders due to important unobserved factors.Helmet use was shown to vary across demographic segments of the motorcyclist population. Use rates were higher among Caucasian riders, as well as among those age 60 and above. No significant difference was observed between male and female riders. Use was also found to vary geographically, temporally, and with respect to various environmental characteristics. Geographically, helmet use rates tended to be correlated with historical restraint use trends, which may be reflective of riding environment and general differences in the riding population. To this end, rates were also highly variable based upon the type of motorcycle and whether the motorcyclist was wearing high-visibility gear.The study results demonstrate the short-term reduction in helmet use following transition from a universal to partial motorcycle helmet law. The reduction in use is somewhat less pronounced than has been experienced in other states, which may be reflective of general differences among Michigan motorcyclists because the state has also generally exhibited higher use rates of seat belts and other forms of occupant protection. The study results also highlight potential target areas for subsequent education and public awareness initiatives aimed at increasing helmet use.

Objective: Driving under the influence of alcohol is a crime that places the lives of all motorists in danger. Though it is a largely preventable act, impaired driving has accounted for 31 to 38% of fatal crashes across the country over the last decade. When an impaired operator crashes his or her vehicle, there is often a second unit, of which the operator is not impaired, involved in the crash. Methods: This research looks at approximately 14,000 2-unit crashes involving an impaired operator in the State of Ohio from 2008 through 2012. The research is focused on determining the effects of crash and operator characteristics in 2-unit alcohol-related crashes through the use of 2 mixed logit models. Results: It is found that several factors have similar effects on the injury severities of both the impaired and nonimpaired operators, including head-on crashes, the use of seat belts, and the deployment of airbags. There are, however, several factors that affect the 2 operators differently. It is found that the impaired operator's injury severity is based on the type and, more important, the size of the vehicle he or she is driving, the roadway geometry, and the speed of the vehicle driven by the nonimpaired operator. The nonimpaired operator is equally affected by the speed of the impaired vehicle as much as his or her own speed, and the nonimpaired operator's injury severity is virtually independent of the type of vehicle being driven. Conclusions: Researchers may disseminate the results to community groups such as Mothers Against Drunk Driving and Safe Communities to increase awareness of the dangers of drunk driving in an effort to reduce the number of alcohol-related crashes.

Recently, nationwide speed limit policy modifications have resulted in a general upward trend in many states, including Michigan. In Michigan legislation has been proposed to raise posted speed limits on limited access freeways for passenger vehicles and for trucks and buses. In response, research was performed to assess the economic impacts associated with speed limit policy alternatives under consideration. The economic assessment included estimation of the agency costs and user benefits and disbenefits for each proposed policy alternative, including those related to infrastructure modifications, fuel consumption, travel time, and fatal crash occurrence. Calculation of the benefit–cost ratios indicated several findings. First, scenarios that increased only the freeway truck and bus speed limit from 60 mph to 65 or 70 mph had favorable benefit–cost ratios (i.e., greater than 1) as long as diesel prices remained below approximately $3 per gallon and fatal crashes did not increase by more than one per year systemwide. However, implementation of the 75 or 80 mph maximum freeway speed limit for passenger vehicles (70 mph for trucks and buses) in general resulted in unfavorable benefit–cost ratios. The reasons in large part were the expected increase in fatal crash occurrence, coupled with substantial infrastructure costs associated with geometric modifications that ultimately would be necessary to achieve compliance with state and federal design speed requirements. Therefore, freeway speed limit increases should be considered only for segments that have low historical crash rates and where design speed compliance can be maintained in general without costly geometric upgrades.

Cross-median crashes are among the most hazardous collision types on freeways. The primary countermeasure to reduce such crashes is the installation of a median barrier, with a cable barrier being a widely used alternative. As of 2014, approximately 317 mi of cable median barriers had been installed on freeways throughout Michigan. To assess the safety impacts of this installation program, a comprehensive before-and-after crash analysis was conducted; this analysis included a manual crash report review to identify all median-related crashes. Safety performance functions were developed for roadway segments before and after cable barrier installation, as well as for similar control segments where no barrier had been installed. The empirical Bayes (EB) method was used to develop crash modification factors as a function of median width. To explore the effects of regression to the mean (RTM), the EB results were compared with those from a naïve before–after analysis. The results showed that cable barriers significantly reduced the frequency of fatal and severe injury crashes, although substantial increases in less severe crashes were also observed. The cable barrier was found to have greater impacts on crashes across nearly all severity levels when used on narrow medians (i.e., 26 to 50 ft) compared with wider medians (50 to 94 ft). In addition, reductions in fatal and serious injuries were less pronounced when compared with prior research (especially for wider medians), which was largely attributed to RTM effects. Ultimately, this study provides important guidance to deal with the expected safety impacts (and related costs) associated with cable median barrier installation.

Speed management has been a long-standing concern of transportation agencies. Recently, nationwide speed limit policy modifications have resulted in a general upward trend in many states. In Michigan, legislation was proposed to raise the maximum speed limits on state-owned, rural, nonfreeway highways from 55 to 65 mph. In response to this proposed speed limit policy change, research was performed to assess the associated economic impacts through the use of benefit–cost analysis. Several potential implementation scenarios of the proposed speed limit policy were investigated; these included a limited subset of roadways with favorable geometry and full statewide implementation. A primary research task was to estimate the costs for infrastructure upgrades necessary to achieve compliance with state and federal design speed requirements for the cohort of roadways included within each 65 mph implementation scenario. User benefits and disbenefits associated with the proposed speed limit increase also were estimated, which included reduced travel times, increased fuel consumption, and increased traffic crashes. Although the travel time savings were estimated to exceed the fuel consumption costs, the resulting benefit was far outweighed by crash-related disbenefits and agency infrastructure costs for roadways that required major geometric modifications (e.g., vertical or horizontal realignment). Consequently, an increase in the speed limit to 65 mph on rural, nonfreeway highways should be considered only if the critical geometric elements can maintain design speed compliance without major modification. However, even for roadways on which design speed compliance is maintained, careful, site-specific consideration must be given to the potential safety impacts, particularly with respect to fatal and injury crashes, which may result after the speed limit is increased.

Lane departures are a precipitating event in most fatal crashes in the United States. This problem is particularly pronounced on high-speed undivided highways, which are prone to cross-centerline crashes. A common countermeasure to reduce such crashes involves installing centerline rumble strips (CLRS), which provide an audible and tactile warning to alert drivers of an impending lane departure event. This study assessed the safety effects of a statewide CLRS implementation program conducted by the Michigan Department of Transportation (DOT) between 2008 and 2010. This program included the installation of CLRS across the Michigan DOT–maintained network of rural, high-speed nonfreeway facilities. Shoulder rumble strips (SRS) were installed in combination with the CLRS at locations with paved shoulders at least 6 ft in width. The empirical Bayes method was used to assess the effectiveness of 4,077 mi of two-lane highways where CLRS were installed as part of this initiative. CLRS were found to reduce target cross-centerline crashes by 27.3% and by 32.8% when used in combination with SRS. Rumble strips were also effective in reducing crashes that occurred under adverse pavement conditions or involved passing maneuvers or driver impairment. This study also provides important insights as to the identification of target (i.e., cross-centerline) crashes. A comprehensive manual review of more than 70,000 crash report forms demonstrated that approximately 10% of target crashes were misclassified by crash type, which is the predominant field typically used to identify such crashes.

The purpose of this study was to examine the travel speed characteristics of passenger vehicles, trucks, and buses in states with different speed limit policies, primarily to ascertain the effects of differential speed limits (DSLs) versus those of uniform speed limits (USLs) for large vehicles. Spot-speed studies were conducted in the neighboring states of Indiana, Michigan, and Ohio; these studies permitted examination of speed characteristics under several speed limit settings along the same freeways. The sites included urban and rural locations, with speed limits at individual locations that varied from 55 to 70 mph. These sites included USLs and DSLs, with 5 mph differentials on rural freeways in Indiana and 10 mph differentials at rural locations in Michigan. Spot-speed data were collected at 157 freeway sites in the three states along flat, tangent segments. Regression models were estimated to ascertain differences in the mean speeds, the 85th percentile speeds, and the standard deviation in speeds across locations. The results showed passenger vehicle speeds to be quite consistent across the three states where a common 70 mph limit was in effect. Speeds varied more at locations with lower posted limits and between trucks and buses. Speeds were most consistent in Ohio at locations with higher USLs. The variability in travel speeds for all vehicles was found to be highest on freeways with DSLs, followed by urban freeways with USLs of 55 mph.

Existing research literature has shown that traffic fatalities increase at higher speed limits. A related issue is the establishment of maximum speed limits for trucks and buses. As of 2014, eight states have a differential speed limit in place that establishes a higher limit for passenger vehicles than for trucks and buses. This study aimed to inform the continuing debate regarding the safety impacts of speed limits by comparing states with various speed limit policies. The study included a longitudinal comparison of state-level rural Interstate fatalities in the United States from 1999 through 2011. In addition to an examination of differences in traffic fatalities as a function of maximum speed limits, comparisons were also made between states with differential limits for truck and buses. Random parameter negative binomial models were estimated for annual total and truck-involved fatalities. A random parameter framework allowed for consideration of temporal correlation in annual fatality counts within states as well as for unobserved heterogeneity across states. The results of this study provided further evidence that both overall and truck-involved fatalities increased with maximum speed limits. States with differential speed limits were found to have marginal differences in total fatalities as compared with states with uniform speed limits. However, truck-involved fatalities were significantly lower in states where differential limits were in place. The effects of speed limit policies as well as other covariates were found to vary significantly across states. The random parameter models demonstrated significantly improved goodness of fit as compared with standard Poisson and negative binomial models.

The interaction of motorists and bicyclists, particularly during passing maneuvers, is an area of concern to the bicycle safety community as there is a general perception that motor vehicle drivers may not share the road effectively with bicyclists. This is a particular concern on road sections with centerline rumble strips where motorists are prone to crowd bicyclists during passing events. One potential countermeasure to address this concern is the use of a bicycle warning sign with a “Share the Road” plaque. This paper presents the results of a controlled field evaluation of this sign treatment, which involved an examination of driver behavior while overtaking bicyclists. A series of field studies were conducted concurrently on two segments of a high-speed, rural two-lane highway. These segments were similar in terms of roadway geometry, traffic volumes, and other relevant factors, except that one of the segments included centerline rumble strips while the other did not. A before-and-after study design was utilized to examine changes in motor vehicle lateral placement and speed at the time of the passing event as they relate to the presence of centerline rumble strips and the sign treatment. Centerline rumble strips generally shifted vehicles closer to the bicyclists during passing maneuvers, though the magnitude of this effect was marginal. The sign treatment was found to shift motor vehicles away from the rightmost lane positions, though the signs did not significantly affect the mean buffer distance between the bicyclists and passing motorists or the propensity of crowding events during passing. The sign treatment also resulted in a 2.5 miles/h (4.0 km/h) reduction in vehicle speeds. Vehicle type, bicyclist position, and the presence of opposing traffic were also found to affect lateral placement and speed selection during passing maneuvers.

The extant traffic safety research literature includes numerous examples of studies that assess those factors affecting the degree of injury sustained by crash-involved motor vehicle occupants. One important methodological concern in such work is the potential correlation in injury outcomes among occupants involved in the same crash, which may be due to common unobserved factors affecting such occupants. A second concern is unobserved heterogeneity, which is reflective of parameter effects that vary across individuals and crashes. To address these concerns, a random parameters bivariate ordered probit model is estimated to examine factors affecting the degree of injury sustained by drivers involved in angle collisions. The modeling framework distinguishes between the effects of relevant factors on the injury outcomes of the at-fault and not-at-fault parties. The methodological approach allows for consideration of within-crash correlation, as well as unobserved heterogeneity, and results in significantly improved fit as compared to a series of independent models with fixed parameters. While the factors affecting injury severity are found to be similar for both drivers, the magnitudes of these effects vary between the at-fault and not-at-fault drivers. The results demonstrate that injury severity outcomes are correlated for drivers involved in the same crash. Further, the impacts of specific factors may be over- or under-estimated if such correlation is not accounted for explicitly as a part of the analysis. Various factors are found to affect driver injury severity and the random parameters framework shows these effects to vary across crashes and individuals. The analytical approach utilized provides a useful framework for injury severity analysis.

Roadside rest areas provide valuable and convenient services to road users as well as tangible safety benefits. However, these benefits are not always enough to warrant the costs, and therefore these facilities are not always economically justified. As such, understanding the factors that affect rest area demand is important for transportation agencies to design and maintain these facilities efficiently within their jurisdictions. The effects of nearby comparable facilities and rest areas on the demand characteristics of roadside rest areas have not been well analyzed in previous literature. This paper presents the results of binary logistic regression and negative binomial regression models on the demand characteristics of 47 roadside rest areas in Michigan. These models were developed separately for passenger cars and commercial trucks because the decision-making processes for these types of road users were likely different. Key results include the finding that greater distances between rest areas and n...

On April 13, 2012, Michigan instituted reforms to its long-standing universal helmet law (UHL) and thus became the 28th state with a partial helmet law, which requires helmet use by only a subset of the riding population. Given continuing increases in motorcycle fatalities, helmet use remains a divisive policy issue facing state governments. The existing research literature includes several before-and-after studies that evaluate the effects of changes in motorcycle helmet laws on metrics such as helmet use and statewide motorcycle fatalities. However, a comprehensive assessment of the effects of helmet use laws on the full range of crash injury outcomes is lacking. Important evidence was added to inform the continuing debate about the efficacy of UHLs. A detailed, disaggregate-level study was conducted to assess the degree of injury severity sustained by motorcyclists involved in crashes before and after Michigan's transition from a UHL to a partial helmet law. By controlling for various rider, roadway, t...

Pedestrian and bicycle safety for school-aged children is a particular concern as traffic crashes continue to be a leading cause of death for children 5 to 14 years old. For this concern to be addressed, Safe Routes to School (SRTS) programs have been implemented in communities across the country, with one of the primary objectives being to provide safe and convenient routes for children to walk or bike to school. Unfortunately, SRTS programs allocate limited funding for such projects. Consequently, it is imperative that programs are implemented at locations where they are likely to have the greatest impact. The primary focus of this study was to develop a safety Performance function (SPF) for use in prioritizing candidate schools for SRTS programs. Traffic crashes over a 5-year analysis period were examined and linked to data that included the school enrollment, the socioeconomic and demographic data for each school district, and the functional class of the roadway on which each school was located. Schools on local roads were found to experience more crashes than those located on other, higher-class road facilities. Crashes also varied with average family size, number of parents per household, population density, and median family income. Crashes were less frequent in school districts that exhibited greater ethnic diversity. The SPF developed as a part of this research can be used for prioritization of candidate schools as well as to assess the efficacy of SRTS programs on a longitudinal basis and thus provide a valuable tool for school administrators and others involved in child pedestrian and bicycle safety.

Although a considerable amount of prior research has investigated the impacts of speed limits on traffic safety and operations, much of this research, and nearly all of the research related to differential speed limits, has been specific to limited access freeways. The unique safety and operational issues on highways without access control create difficulty relating the conclusions from prior freeway-related speed limit research to 2-lane highways, particularly research on differential limits due to passing limitations and subsequent queuing. Therefore, the objective of this study was to assess differences in driver speed selection with respect to the posted speed limit on rural 2-lane highways, with a particular emphasis on the differences between uniform and differential speed limits.Data were collected from nearly 59,000 vehicles across 320 sites in Montana and 4 neighboring states. Differences in mean speeds, 85th percentile speeds, and the standard deviation in speeds for free-flowing vehicles were examined across these sites using ordinary least squares regression models.Ultimately, the results of the analysis show that the mean speed, 85th percentile speed, and variability in travel speeds for free-flowing vehicles on 2-lane highways are generally lower at locations with uniform 65 mph speed limits, compared to locations with differential limits of 70 mph for cars and 60 mph for trucks.In addition to posted speed limits, several site characteristics were shown to influence speed selection including shoulder widths, frequency of horizontal curves, percentage of the segment that included no passing zones, and hourly volumes. Differences in vehicle speed characteristics were also observed between states, indicating that speed selection may also be influenced by local factors, such as driver population or enforcement.

Public rest areas along limited-access freeways throughout the United States allow quick access and free 24-h availability to basic amenities such as parking and restrooms. The recent economic downturn has made it increasingly difficult for state agencies to maintain rest areas and has forced many states to consider downsizing services or closing facilities. Although rest areas provide many benefits to motorists, the safety and economic impacts associated with rest areas and traveler information centers have proved difficult to quantify. A benefit–cost (B-C) analysis methodology was developed for public rest areas and traveler information centers on limited-access freeways. This methodology considered a broad range of benefits associated with public rest areas, including travel diversion savings, comfort and convenience benefits, and crash reductions. Increased tourism spending was also considered for traveler information centers. The costs were almost exclusively related to those incurred by the agency, which included construction, rehabilitation, operation, and routine maintenance. The methodology was demonstrated with data provided by the Michigan Department of Transportation. Because the estimated benefits were strongly correlated with annual use of the facility, the facilities with the highest B-C ratios included heavily used facilities located on the primary freeway routes. Those with the lowest B-C ratios were underused facilities with high operation or maintenance costs.

Fatigue-related crashes account for 2.2% to 2.6% of all fatal crashes in the United States on an annual basis. These types of crashes are prevalent in rural areas, and public roadside rest areas were developed largely to alleviate motorist fatigue and reduce the opportunity for such crashes by providing safe parking areas for tired drivers. However, research about the safety effects of rest areas has been limited. Results are presented of a spatial analysis that investigates how a road segment's proximity to a rest area affects the frequency of fatigue-related crashes. Poisson and negative binomial models are estimated for freeways and two-lane highways to isolate the effects of proximity while controlling for other relevant factors, such as traffic volume. The results of these models indicate that the proximity of a road segment to the nearest rest area significantly influences crash frequencies on both freeways and two-lane highways, where traffic volumes tended to have similar effects, although the effects of proximity were slightly more pronounced on two-lane highways. The study results suggest that roadside rest areas provide a safety benefit, and the crash prediction models developed as a part of this research provide a starting point for quantifying these impacts.

Traffic incidents are a principal cause of congestion on urban freeways, reducing capacity and creating risks for both involved motorists and incident response personnel. As incident durations increase, the risk of secondary incidents or crashes also becomes problematic. In response to these issues, many road agencies in metropolitan areas have initiated incident management programs aimed at detecting, responding to, and clearing incidents to restore freeways to full capacity as quickly and safely as possible. This study examined those factors that impact the time required by the Michigan Department of Transportation Freeway Courtesy Patrol to clear incidents that occurred on the southeastern Michigan freeway network. These models were developed using traffic flow data, roadway geometry information, and an extensive incident inventory database. A series of parametric hazard duration models were developed, each assuming a different underlying probability distribution for the hazard function. Although each modeling framework provided results that were similar in terms of the direction of factor effects, there was significant variability in terms of the estimated magnitude of these impacts. The generalized F distribution was shown to provide the best fit to the incident clearance time data, and the use of poorer fitting distributions was shown to result in severe over-estimation or under-estimation of factor effects. Those factors that were found to impact incident clearance times included the time of day and month when the incident occurred, the geometric and traffic characteristics of the freeway segment, and the characteristics of each incident. Copyright © 2012 John Wiley & Sons, Ltd.

A before-and-after field evaluation assessed the impacts that centerline and shoulder rumble strips on rural two-lane roadways have on various characteristics of driver behavior. The following characteristics were assessed as part of this evaluation: passing maneuvers, lateral lane placement, and centerline and edgeline encroachments. The data were collected with video cameras temporarily installed at 18 passing zones and 12 curves on rural two-lane roadways throughout Michigan. The cameras were installed at the same locations before and after the installation of rumble strips. A manual review of the videos was performed to assess the various behavioral characteristics. Nearly 78,000 vehicles were observed during review of the passing zone videos, and more than 50,000 vehicles were observed during review of the curve videos. Centerline rumble strips were found to improve driver central lane positioning tendencies and decrease the occurrence of centerline encroachments. The inclusion of shoulder rumble strips in addition to centerline rumble strips provided incremental improvements in central lane positioning and reduced edgeline encroachments. Most notable, centerline and shoulder rumble strips greatly reduced the occurrence of drivers laterally shifting to the inside while maneuvering through curves (i.e., corner cutting). In addition, centerline rumble strips did not reduce the rate of passing maneuvers. Collectively, these results suggest that both centerline and shoulder rumble strips have a positive impact on surrogate measures for roadway safety and do not negatively affect driver behavior.

Reducing the severity of injuries resulting from motor-vehicle crashes has long been a primary emphasis of highway agencies and motor-vehicle manufacturers. While progress can be simply measured by the reduction in injury levels over time, insights into the effectiveness of injury-reduction technologies, policies, and regulations require a more detailed empirical assessment of the complex interactions that vehicle, roadway, and human factors have on resulting crash-injury severities. Over the years, researchers have used a wide range of methodological tools to assess the impact of such factors on disaggregate-level injury-severity data, and recent methodological advances have enabled the development of sophisticated models capable of more precisely determining the influence of these factors. This paper summarizes the evolution of research and current thinking as it relates to the statistical analysis of motor-vehicle injury severities, and provides a discussion of future methodological directions.

The purpose of this study was to examine statewide motorcycle crash data from the state of Ohio to identify those factors most strongly associated with the level of injury sustained by motorcyclists involved in crashes. The year 2009 marked the first time since 1997 that Ohio experienced fewer motorcycle fatalities than in the previous year; this result was consistent with national trends over this same period. Since anecdotal evidence suggested that much of this result was due to decreases in motorcycle travel, an investigation of rider, crash, and environmental factors that influenced injury severity was an important step toward sustaining this reduction. The effects of such factors in various types of motorcycle crashes were compared. Multinomial logit models were developed for single-vehicle and multivehicle motorcycle crashes at both intersection and nonintersection locations. The results showed that the impacts of relevant crash factors varied by crash type and location and that severe injuries were more likely when high speed or alcohol was involved. Collisions with fixed objects and high-impact crashes, such as angle and head-on collisions, also produced dramatic increases in injury severity. Helmet use continued to provide the most promising means of reducing severe and fatal injuries in all types of crashes. Helmet use was found to reduce the likelihood of injury by 34.4% in single-vehicle crashes and between 12.4% and 14.1% in multivehicle crashes.

Research was performed to explore the impact on driver behavior of steady-burn warning lights on drums used in highway work zones in the state of Michigan. Various characteristics related to nighttime driver behavior were evaluated with data collected in actual work zones. Thirty-six randomly selected work zones in 15 counties throughout lower Michigan were investigated in this study. Collectively, the work zones represented a broad range of commonly occurring scenarios. Work zones that used drums with steady-burn warning lights and work zones that did not were examined in a comparative parallel study. Data on nighttime driver behavior were collected by recording the movements of randomly selected subject vehicles as they were followed by a survey vehicle through the study work zones. For each subject vehicle, three measures of driver behavior were collected. The measures were (a) percent of time spent in the center lane position, (b) percent of time spent in the lane position closest to the drums, and (c) rate of steering reversals per minute. The data were compared by using analysis of variance techniques. The results showed that the presence of steady-burn warning lights on drums used to channelize traffic in work zones did not significantly affect either the time vehicles spent in the center lane position or the rate of steering reversals. The presence of steady-burn warning lights did, however, increase the tendency of drivers to travel in relatively close proximity to the drums. Collectively, the research findings suggest that the use of steady-burn warning lights on channelizing drums in work zones does not have a substantive impact on nighttime driver behavior.

The purpose of this study was to develop, test, and evaluate two pilot enforcement programs aimed at the improvement of pedestrian safety in the city of Detroit, Michigan, through reductions in the incidence of pedestrian traffic violations. Separate targeted enforcement programs were conducted in coordination with the Detroit Police Department and the Wayne State University Police Department. Both programs demonstrated that targeted enforcement could be used to reduce the rate of pedestrian traffic violations effectively and that these changes could be sustained for some time after enforcement had been completed. The city-wide program was found to reduce violations by up to 17.1% during the enforcement period, with sustained reductions of 7.8% being detected several weeks after enforcement was completed. Similarly, the program on the Wayne State University campus reduced violations by 27% during enforcement and showed sustained reductions of 9.8%. The results generally varied on a case-by-case basis, and infrastructure deficiencies contributed to increased violations. As a part of this study, a strategy for collection of data in the field was developed. The strategy allowed the covert, unobtrusive monitoring of pedestrian behavior during the periods before, during, and after enforcement.

Motorcycle crashes and fatalities have been increasing rapidly during the past 12 years both in Ohio and across the rest of the United States. In response to these issues, various studies have examined aspects of motorcycle safety in recent years. However, there has been limited research on the effects of site-specific roadway geometry on the frequency of motorcycle crashes, particularly at nonintersection locations. Typically, researchers employ Poisson and negative binomial crash prediction modeling techniques in these types of studies. The research presented in this paper uses a negative binomial model, applying full Bayes methods to improve model performance and to assess the impacts of horizontal curvature and other geometric features on the frequency of single-vehicle motorcycle crashes along segments of rural two-lane highways. The data used in this study include crash records for the years 2002 through the spring of 2008, in combination with available geometric design information, for those curves maintained by the State of Ohio. The analysis data set includes 30,379 horizontal curves that experienced a total of 225 motorcycle crashes during the study period. The findings show that the radius and length of each horizontal curve significantly influence the frequency of motorcycle crashes, as do shoulder width, annual average daily traffic, and the location of the road segment in relation to the curve.

Horizontal curves have been identified as a target area for improving safety on rural two-lane highways in Texas. This study involved the development of multinomial logit models to assess driver injury severity resulting from single-vehicle crashes on such roads. Likelihood ratio tests warranted the development of separate injury severity models for curves of small, medium, and large radius. Various driver, vehicle, roadway, and environmental characteristics were found to affect injury severity among the 10,029 crashes analyzed. Run-off-the-road crashes, particularly those resulting in collisions with roadside objects, were found to increase injury severity significantly. Females were more likely to sustain injury and older drivers to be critically injured, particularly on curves of smaller radius. Various driver actions and behaviors were also significant determinants of injury severity. Unbelted drivers were up to 10 times more likely to suffer fatal injuries, and drivers who were uninsured, fatigued, or under the influence of drugs or alcohol were more likely to be seriously injured. Several of these behavioral factors were more pronounced on sharper curves.

Michigan is plagued by more than 60,000 deer–vehicle crashes on an annual basis. Although the majority of these crashes result in property damage only, a substantial number lead to significant injuries and fatalities, illustrating the need for a better understanding of the many interrelated factors that affect crash severity. A database of all single-vehicle deer–vehicle crashes (DVC) reported to Michigan law enforcement agencies between January 1, 2004, and December 31, 2005, was used to estimate a multinomial logit model of driver injury severity. Results revealed a number of driver, vehicle, and environmental factors that significantly influenced injury severity. Younger drivers were more likely to be injured as a result of a DVC, a possible indication of a lack of appropriate skills or knowledge on the part of these drivers when they encounter deer on the roadway. Female drivers were found to be at an increased risk of injury, as were drivers who had a passenger in the vehicle at the time of the crash. Seatbelt and airbag usage were found to be the most effective means of reducing the likelihood of severe injuries, although airbags did increase the likelihood of minor injuries. Impacting deer head-on and avoiding run-off-the-road collisions were also found to reduce the propensity of injury. Educational and enforcement initiatives, such as the “Don't Veer for Deer” campaign, may provide a cost-effective means of combating the DVC problem.

Persistent increases in motorcycle fatalities and injuries in recent years have heightened safety awareness and have focused attention on the role that motorcyclist training and education can play in reducing accident rates. In this study a 2005 sample of Indiana motorcyclists was used to estimate statistical models of the effectiveness of existing training programs in reducing accident probabilities. Statistical models relating to motorcyclist speed choice and helmet usage behavior were also estimated. The findings showed that those individuals who took beginning rider training courses were more likely to be involved in an accident than those who did not and that those who took the beginning course more than once were much more likely to be involved in an accident. Although explanations for these findings can range from the use of ineffective course material to changes in risk perception as a result of taking the course, another explanation is that riders who take the course are inherently less skilled than those who do not. The findings underscore the need for a careful and comprehensive study of rider skills and risk perceptions to maximize the effectiveness of motorcycle training courses.

Controlled field studies were performed at 12 locations to evaluate the impacts of milled centerline rumble strips on exterior roadside noise adjacent to rural two-lane highways as a function of rumble strip depth and pavement type. Twenty controlled pass-bys were performed at each location using a minivan traveling at 88.5 km/h (55 mph). An equal number of passes were made both while traveling on and off of the centerline rumble strips, with the latter condition providing baseline noise data. The maximum noise was recorded during each pass using a digital sound meter that was placed 15.24 m (50 ft) laterally from the centerline of the roadway at a height of 1.52 m (5 ft) above the pavement surface. Multiple linear regression models were estimated to ascertain the effects of depth and pavement type while controlling for baseline noise. The milled depth of the rumble strips was the strongest predictor of roadside noise, and this effect was stronger for hot mix asphalt pavements compared to chipsealed pavements. For every 1.5875 mm (1/16-in.) increase in centerline rumble strip depth, roadside noise increased by 2.3 decibels on hot mix asphalt pavements, compared to 1.4 decibels on chipsealed pavements.

INTRODUCTION: The effects of cell phone use and safety belt use have been an important focus of research related to driver safety. Cell phone use has been shown to be a significant source of driver distraction contributing to substantial degradations in driver performance, while safety belts have been demonstrated to play a vital role in mitigating injuries to crash-involved occupants. METHOD: This study examines the prevalence of cell phone use and safety belt non-use among the driving population through direct observation surveys. A bivariate probit model is developed to simultaneously examine the factors that affect cell phone and safety belt use among motor vehicle drivers. RESULTS: The results show that several factors may influence drivers' decision to use cell phones and safety belts, and that these decisions are correlated. PRACTICAL APPLICATIONS: Understanding the factors that affect both cell phone use and safety belt non-use is essential to targeting policy and programs that reduce such behavior. Keywords: Driver distraction; Language: en

Motorcycle crashes frequently involve a combination of high-risk behaviors by the motorcyclist or the other crash-involved driver. Such behaviors may include riding or driving without appropriate licensure or while under the influence of alcohol, as well as deciding not to use a safety device such as a helmet or safety belt. Given that these factors frequently occur in combination with one another, it is difficult to untangle the specific effects of individual factors leading up to the crash outcome. This study assesses how various rider-, driver-, and other crash-specific factors contribute to at-fault status in two-vehicle motorcycle crashes, as well as how these same factors affect the propensity for other high-risk behaviors. Furthermore, the interrelationships among fault status and these other behaviors are also examined using a multivariate probit model. This model is developed using police-reported crash data for the years 2006-2010 from the State of Ohio. The results show that younger motorcyclists are more likely to be at-fault in the event of a collision, as are riders who are under the influence of alcohol, riding without insurance, or not wearing a helmet. Similarly, motorcyclists were less likely to be at-fault when the other driver was of younger age or was driving under the influence of alcohol, without insurance, or not wearing their safety belt. Crash-involved parties who engaged in one high-risk behavior were more likely to engage in other such behaviors, as well, and this finding was consistent for both motorcyclists and drivers. The results of this study suggest that educational and enforcement strategies aimed at addressing any one of these behaviors are likely to have tangential impacts on the other behaviors, as well.

Standard multinomial logit (MNL) and mixed logit (MXL) models are developed to estimate the degree of influence that bicyclist, driver, motor vehicle, geometric, environmental, and crash type characteristics have on bicyclist injury severity, classified as property damage only, possible, nonincapacitating or severe (i.e., incapacitating or fatal) injury. This study is based on 10,029 bicycleinvolved crashes that occurred in the State of Ohio from 2002 to 2008. Results of likelihood ratio tests reveal that some of the factors affecting bicyclist injury severity at intersection and non-intersection locations are substantively different and using a common model to jointly estimate impacts on severity at both types of locations may result in biased or inconsistent estimates. Consequently, separate models are developed to independently assess the impacts of various factors on the degree of bicyclist injury severity resulting from crashes at intersection and non-intersection locations. Several covariates are found to have similar impacts on injury severity at both intersection and non-intersection locations. Conversely, six variables were found to significantly influence injury severity at intersection locations but not non-intersection locations while four variables influenced bicyclist injury severity only at non-intersection locations. In crashes occurring at intersection locations, the likelihood of severe bicyclist injury increases by 14.8 percent if the bicyclist is not wearing a helmet, 82.2 percent if the motorist is under the influence of alcohol, 141.3 percent if the crash-involved motor vehicle is a van, 40.6 percent if the motor vehicle strikes the side of the bicycle, and 182.6 percent if the crash occurs on a horizontal curve with a grade. Results from non-intersection locations show the likelihood of severe injuries increases by 374.5 percent if the bicyclist is under the influence of drugs, 150.1 percent if the motorist is under the influence of alcohol, 53.5 percent if the motor vehicle strikes the side of the bicycle and 99.9 percent if the crash-involved motor vehicle is a heavy-duty truck.

Motorcycle fatalities have more than doubled in the United States since 1997--highlighting the need to better understand the many interrelated factors that determine motorcyclists' crash-injury severities. In this paper, using a detailed crash database from the state of Indiana, we estimate probabilistic models of motorcyclists' injury severities in single- and multi-vehicle crashes. Nested logit (estimated with full information maximum likelihood) and standard multinomial logit model results show a wide-range of factors significantly influence injury-severity probabilities. Key findings show that increasing motorcyclist age is associated with more severe injuries and that collision type, roadway characteristics, alcohol consumption, helmet use, unsafe speed and other variables play significant roles in crash-injury outcomes.

In recent years, the State of Indiana has built a number of intersections where one or both of the roads are located on curves. The AASHTO Policy on Geometric Design of Highways and Streets recommends that in such cases “the alignment should be as straight and the gradient as flat as practical.” This wording, consistent with Part V of the Indiana Design Manual, allows for the design of intersections on curves if other solutions prove to be too expensive. Several of these intersections have raised safety concerns and led to expensive corrective measures. Due to these safety and economic issues, INDOT currently avoids designing intersections on segments with steep superelevation. The focus of this research is to determine what effect curvature and superelevation have on intersection safety. Based on the results, the goal is to provide design standards for curvature and superelevation for cases where the major road is located on a superelevated curve.

INTRODUCTION: Alcohol related crashes have accounted for approximately 35% of fatal crashes per year since 1994 nationwide, with approximately 30% involving impairment over the legal blood alcohol content limit of 0.08%. Educational campaigns and law enforcement efforts are two components of multi-faceted programs aimed toward reducing impaired driving. It is crucial that further research be conducted to guide the implementation of enforcement and educational programs. METHOD: This research attempts to provide such guidance by examining differences in alcohol-involved crashes involving motorcycles and passenger cars. Prior safety research has shown that motorcyclists follow a significantly different culture than the average passenger car operator. These cultural differences may be reflected by differences in the contributing factors affecting crashes and the severity of the resulting injuries sustained by the driver or motorcyclist. This research is focused on single-vehicle crashes only, in order to isolate modal effects from the contribution of additional vehicles. The crash data provided for this study are from the Ohio Department of Public Safety from 2009 through 2012. RESULTS: The injury severity data are analysed through the development of two mixed logit models, one for motorcyclists and one for passenger car drivers. The models quantify the effects of various factors, including horizontal curves, speeds, seatbelt use, and helmet use, which indicate that the required motor skills and balance needed for proper motorcycle operation compounded with a lack of mechanical protection make motorcyclists more prone to severe injuries, particularly on curves and in collisions with roadside objects. PRACTICAL APPLICATIONS: The findings of this study have been incorporated into combined motorcycle and sober driving educational safety campaigns. The results have shown to be favorable in supporting national campaign messages with local justification and backing. Language: en