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This study investigates a driving behavior referred to as the cooperative safety concept that assumes for strings of conventional vehicles traveling in nighttime or conditions with reduced visibility during a stable flow condition, the leading vehicles would bear much of the navigational challenges and risks while the following vehicles enjoy reduced driving workload and improved navigation safety. The study includes a comprehensive investigation of the safety risk levels and driver behaviors at intersections and freeway ramp locations in an attempt to verify this phenomenon using data from the large-scale Second Strategic Highway Research Program (SHRP 2) naturalistic driving study database. Overall, the driver behavior analysis showed that drivers following other vehicles tended to travel at lower speeds but with more acceleration activities than other vehicles. In addition, lighting during nighttime appeared to help alleviate the behavioral differences between the two types of travelers and resulted in more dispersed merging, diverging, and lane-changing behaviors. The safety event data analysis showed that higher traffic levels tended to correlate with more safety events in general but significantly fewer single-vehicle events. In addition, higher traffic levels correlated with a significantly lower likelihood of crashes in general when a safety event occurred. In the SHRP 2 data, safety events included crashes, near crashes, and statistically selected baseline events recorded during the data collection. The findings of this study, including in particular the event analysis, indicated that vehicles following other vehicles in a free-flow condition tended to drive slower and have lower safety risks in terms of crashes in general and single-vehicle crashes in particular. This knowledge can have significant implications for applications such as advanced lighting systems, cooperative vehicle features, and smart traffic control strategies. [ABSTRACT FROM AUTHOR]

Horizontal curves tend to be associated with a disproportionate number of severe crashes. Roadway departure crashes are the most frequent crash types on horizontal curves and are highly influenced by driver behavior in conjunction with roadway and environmental factors. Failure to maintain proper lane position along the curve is one of the reasons for an increase in roadway departure crashes. The primary aim of any curve-related treatment is to influence vehicle travel paths by reducing the undesirable paths and thus assist in improving vehicular safety along horizontal curves. To date, an analysis of vehicle travel paths as a function of various factors that influence travel path behavior has not been conducted. The objective of this study is to develop models to predict vehicle travel paths along horizontal curves as a function of curve geometric, pavement, and traffic control characteristics. Lane width, curve sharpness, and speed differential have been identified as key geometric variables. Skid number, which describes the skid resistance of a pavement, was found to significantly influence vehicle travel paths. [ABSTRACT FROM AUTHOR]

Adaptive traffic-signal control (ATSC) is a traffic management strategy in which traffic-signal timings change, or adapt, based on observed traffic demand. Although ATSC can improve mobility, it also has the potential to reduce crashes because mainline stops should be reduced. This paper aims to evaluate the safety effectiveness of ATSC using the empirical Bayes method. This analysis examines 47 urban or suburban intersections where ATSC was deployed in Virginia using 235 site-years of before data and 66 site-years of after data. Installing ATSC was found to produce a crash modification factor (CMF) for total intersection crashes of 0.83 with a standard error of 0.05. This CMF was statistically significant at a 95 percent confidence level. Fatal and injury crashes did not change by a statistically significant amount, indicating that the primary safety benefit of ATSC was reduction in property damage crashes. Analyses of ATSC safety effects by crash type, by traffic volume level, and by operational improvement magnitude were also performed. All crash types were found to be reduced, but safety benefits varied from corridor to corridor and by volume levels. It was concluded that ATSC installation can potentially reduce total crashes at highway intersections and that public agencies should consider ATSC’s safety and mobility benefits when justifying ATSC projects. [ABSTRACT FROM AUTHOR]

Signage plays an important role in work zones to provide guidance to drivers under changed conditions. This study investigated the safety effect of an alternative merge sign configuration in a freeway work zone. In this alternative configuration, the graphical-only lane closed sign from the Manual on Uniform Traffic Control Devices (MUTCD) was compared against a MERGE/arrow sign on one side and a Right Lane Closed sign on the other side. Although the graphical-onlyMUTCD signage for work zones has been in use for several years, it is not known if the signage recommended by the MUTCD offers the highest safety for all jurisdictions. The study measured driver behavior characteristics including speeds and open lane occupancies. The measurements were taken at a work zone on Interstate 70 in Missouri. The study found that the open lane occupancy upstream of the merge sign was higher for the test sign in comparison to the MUTCD sign. The occupancy values at different distances between the merge sign and the taper were similar for both signs. The test sign had 11% more traffic in the open lane upstream of the merge sign. In terms of safety, it is desirable for vehicles to occupy the open lane as far upstream from the taper as possible to avoid conflicts due to the lane drop. The analysis of speed characteristics did not reveal substantial differences between the two sign configurations. The 85th percentile speeds with theMUTCD sign were only 1.6 and 3.2 kph (1 and 2 mph) lower than the test sign at the merge sign and taper locations, respectively. In considering all the aforementioned performance measures, the alternative sign configuration was not superior, but performed equal to the MUTCD sign configuration. [ABSTRACT FROM AUTHOR]

Toll plazas create a number of bottlenecks on highways. They can induce motor vehicle crashes and also put workers such as toll collectors at risk. Enhancing safety at toll plazas is crucial to improving safety on tolled roadways. This study aims to evaluate the safety effects of removing mainline barrier toll plazas on highways using empirical Bayesian (EB) methodology. Recent removals of barrier toll plazas on the Garden State Parkway in New Jersey were used as a case study. Multiple-year traffic and crash data before and after the removals of the barrier toll plazas were used for evaluation. Toll plaza crash frequency models as a function of traffic flow and other relevant factors were developed, with the modeling results suggesting that there is a nonlinear relationship between toll plaza crash occurrences and both traffic flow as well as tollbooth configurations. The EB approach is also used to predict crash frequency assuming that the barrier tollbooths were not removed. These EB-based estimates were compared with the observed number of crashes after the removals of the toll plazas. Individual comparisons show reductions in crash occurrence at almost all of the toll plazas and an estimated reduction of 42.1% overall at all toll plazas due to the removal of the barrier tollbooths. The estimated crash cost was reduced by 40.1%. These estimated reductions demonstrate that the removal of barrier toll plazas is a very beneficial countermeasure towards improving safety of toll roads. As the study was performed based on multiple sites along a highway, it would be helpful to learn more lessons from other locations given the availability of reliable data for model development and validation. [ABSTRACT FROM AUTHOR]

The authors present a procedure for allocating resources for implementing safety improvement alternatives at urban intersections over a multiyear planning horizon. The procedure, on the basis of optimization techniques, attempts to maximize benefits measured in dollars saved by reducing crashes of different severity categories subject to budgetary and other constraints. It is presented in two parts: (1) a base case including the objective function and a set of mandatory constraints; and (2) additional policy constraints/special features that can be separately incorporated to the base case. Demonstration of the procedure is presented on intersections in the Detroit metropolitan region, in which economic losses resulting from traffic crashes at intersections are estimated to exceed $4 billion annually. The proposed model can allocate resources for safety improvement alternatives over a planning horizon, given a number of independent locations and a number of mutually exclusive alternatives at each location. The policy constraints provide the analyst the flexibility of adding equity, urgency, and other features to the base case. An integer programming technique is applied to solve the demonstration problem. [ABSTRACT FROM AUTHOR]

Signalized intersections are provided in traffic networks to improve the safety and efficiency of vehicular and pedestrian movement. Various measures under education, enforcement, and engineering headings being attempted to improve the safety and efficiency of operations at signalized intersections. Provision of signal countdown timer, a timer showing the remaining red and green time in a phase, is one such measure and is commonly adopted in India. However, studies on the effects of a countdown timer under Indian traffic conditions are very scarce. Traffic heterogeneity and lack of lane discipline make the transferability of models developed in other countries (with more organized traffic) infeasible. The present study is an attempt to analyze the changes in queue-discharge characteristics and red-light violations (RLVs) under Indian traffic conditions due to the presence of a timer. A before-and-after analysis was carried out using the data collected from a selected intersection in Chennai, India. The analysis was carried out for different vehicle types in the presence and absence of timers separately for the start and end of red/green. Results showed that the information provided at the start of green (end of red) enhances efficiency, the start-up lost time is reduced, and there is an increase in RLVs. Two-wheelers present at the start of the queue are found to be the category that is mostly affected by this information. However, the information provided at the end of green (start of red) was found to reduce the incidence of RLVs. In the presence of information, it was found that the propensity of RLV (proportion of cycles having RLV) decreased from 59 to 31% at the end of green (start of red) and increased from 12 to 75% at the start of green (end of red) with a statistically significant drop in the headways (indicating an increased efficiency). Also, in the presence of information, the intensity of RLVs (mean RLVs per RLV cycle) for both the start of red and end of red decreased from 3.32 to 2.30 vehicles and 8.52 to 5.60 vehicles, respectively. The impacts varied based on vehicle type with major impacts on two-wheelers. The queue-discharge models show a significant change in trend, implying a need to update the signal timings when timers are installed. These results also bring to light the trade-off between safety and efficiency and the choices drivers make in the presence of phase-change information. These trade-offs should be carefully considered as the technology advances and drivers are provided with more and more information. For example, with the advent of intellidrive technology (vehicle-to-infrastructure communications), the extent of information provided to drivers should be tailored to achieve system optimality. The results of studies such as this one can help in decision making. [ABSTRACT FROM AUTHOR]

In recent years, the state departments of transportation have implemented a number of highway rehabilitation projects across the country. These projects differ fundamentally from new highway projects in that they require an uninterrupted flow of traffic throughout both the duration and geometric length of the project. Synchronization of traffic closure with the construction activities is crucial in such projects to avoid the traffic conflicts and prevent idle time for equipment and labor. Although most highway rehabilitation projects involve predominantly linear activities, the techniques of linear scheduling are not readily applicable to highway rehabilitation projects due to the conflict between the workzone and traffic flow. This paper documents the development of a traffic closure integrated linear schedule (TCILS) that addresses both traffic closure and work progress issues. The TCILS generates a single schedule for both the construction activities and the associated traffic closures. Visual and graphical features are also applied in the system, which makes it particularly applicable for highway rehabilitation projects. An actual concrete pavement rehabilitation project using the TCILS is presented as a sample of application. The findings from the sample project, although they are limited, show that the TCILS can be applied to an actual project. With recommended future development, the system is believed to be beneficial for both construction practitioners and academics. [ABSTRACT FROM AUTHOR]

Although geographic information systems (GISs) have been applied in different areas of transportation, full use of their potential in speed profile analysis and highway design consistency studies has yet to be made. The possibilities that GISs offer for analysis and the increasing number of highway inventories supported by such systems, including traffic data and crash rates, suggest that the implementation of a highway design consistency analysis module within a GIS will facilitate and improve road safety studies. It is with this aim that a GIS-based computer system that builds vehicle speed profiles and analyzes highway design consistency has been developed, in which an operating speed prediction model, acceleration/deceleration rates, and other features can be configured by the engineering user in order to obtain an analysis that is more representative of drivers and local conditions. Application of this system to the study of the design consistency of highways is described, using three examples. [ABSTRACT FROM AUTHOR]

There is a need to investigate educational offerings in highway safety available through engineering, public health, and injury prevention programs at universities in the United States. A series of surveys was distributed to universities and transportation engineering research centers throughout the United States from March 2004 to March 2005, requesting information about safety course availability and content (e.g., course outline, syllabus, references, and notes). Of 117 engineering programs contacted, 29 safety courses were identified at 25 universities; of 34 public health programs, only seven indicated traffic safety content. A detailed assessment of course content and syllabi revealed that many use reference materials drawn from other areas of transportation (e.g., design and operations); few use educational references reflecting contemporary scientific analyses of safety. Existing course content was compared with safety core competencies developed by a Transportation Research Board Subcommittee to provide an indication of adequacy of course content. The comparison indicated relative strengths in identifying origins and characteristics of crash data and safety management systems, but persistent weaknesses in describing highway safety as a field with underlying scientific principles, which drive how analysis is conducted and decisions are made. The courses also lacked a systemic multidisciplinary perspective, important for success in today’s safety management field. While safety is a primary responsibility of transportation engineers, there is a lack of complete and consistent coverage of this topic at the university level. [ABSTRACT FROM AUTHOR]