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Abstract. A queuing system resulting from a signalized intersection regulated by pretimed control in a network of urban traffic is considered. Modeling the queue length and the delay of vehicles [...]

Conditional priority is recognized as having the potential to improve transit service reliability at small cost to general traffic. The popular preference for conditional priority over unconditional priority encounters the challenges of various and challenging test scenarios. This paper makes a comparative analysis of unconditional and conditional priority in terms of intersection performance, based on the logic rule-based bus rapid transit signal priority (BRTSP), an active transit signal priority (TSP) for use at isolated signalized intersections with median bus-only lanes. Compared to previous study, the design of phase scheme, including two BRT phases, eight vehicle phases and four pedestrian phases, and the technical framework of BRTSP, centered on four categories of logic rules, have been improved to incorporate a mechanism for providing phase insertion, a special signal priority treatment in addition to green extension and early green. Phase insertion detector, if phase insertion is desired, is installed on the bus-only lane between check- in and check-out detector to trigger phase insertion request. A new category of logic rules, i.e., rules for early green response, is introduced into as a component of BRTSP to dynamically alter the response of the vehicle phases conflicting with the BRT phases to early green request. Inductive loop detector placed on each lane of the vehicle phases is used to monitor time headway and occupancy time on a lane by lane basis. The simulation experimental results indicated that: (1) phase insertion contributed substantially to late schedule deviations correction, but was recommended to be embedded in conditional priority rather than unconditional priority; (2) there was lack of convincing evidence that conditional priority had an inherent effectiveness of managing the intersection performance by varying the lateness criterion; (3) at TSP-enabled isolated intersections with green extension and early green, compared to having conditional priority, having an integration of unconditional priority and holding early BRT vehicles at control points may be a cost-effective solution not only to improve schedule adherence but also to accommodate the benefits of general traffic; and (4) at TSP-enabled isolated intersections with green extension, early green and phase insertion, there seemed to be a pressing need to move from unconditional priority to conditional priority. DOI: 10.1061/(ASCE)TE.1943-5436.0000179 CE Database subject headings: Buses; Rapid transit systems; Intersections; Traffic signals. Author keywords: Bus rapid transit; Median bus-only lanes; Isolated signalized intersection; Transit signal priority; Phase scheme; Logic rules.

Traditional pedestrian level of service measures at signalized intersections are based on pedestrian space and pedestrian delay. However, these measures may not adequately reflect the negative impact of right-turning traffic on pedestrians. This paper presents a statistical analysis using a binary logit model that provides new insights into the factors that affect the likelihood that a pedestrian is compromised (delayed, altered their travel path, or altered their travel speed) in response to traffic turning right (on green) during concurrent vehicle/pedestrian signal timing. The statistical analysis indicates that a number of factors affect the likelihood of a pedestrian being compromised including pedestrian direction of travel, fight-turn traffic volume, number of pedestrians crossing, whether the pedestrian arrived late and began crossing after the end of the walk interval, and the crosswalk characteristics including location (downtown versus suburban) and one-way/two-way streets. CE Database subject headings: Pedestrians; Traffic safety; Traffic signals; Intersections; Statistics.

In this research, we propose an electro-sensitive traffic light using the smart agent algorithm to reduce traffic congestion and traffic accidents. The multi-agent system approach can provide a new and preferable solution. The proposed method adaptively controls the cycle of traffic signals even though the traffic volume varies. Consequently, we reduce the car waiting time and start-up delay time using fuzzy control of feedback data. In particular, we have designed and implemented a system to create optimum traffic signals in congested conditions. The effectiveness of this method was shown through simulation of multiple intersections. Key words: Traffic signal, smart agent, car, accident, INTRODUCTION Most urban areas nowadays experience severe traffic jams on street networks. As the traffic congestion spreads, there is a need to apply intelligent algorithms to diminish the waste of [...]

In-vehicle traffic lights that assist drivers in crossing intersections are in development; however, the availability of the in-vehicle traffic light will be limited if the waiting time of a vehicle is not considered in actual traffic conditions, especially at priority-controlled unsignalized intersections that normally consist of one major and two minor roads. The present study therefore investigated the effects of the waiting time on driver behaviors to improve the in-vehicle traffic light for the priority-controlled unsignalized intersections. Gap acceptance theory that considers the waiting time was adopted in the implementation of the in-vehicle traffic light, to assist minor-road drivers in passing through the intersections by selecting appropriate major-road gaps. A driving simulator experiment involving 12 participants was performed for the minor and major roads, by applying the in-vehicle traffic light with and without the consideration of waiting time. Results demonstrate that the maximum acceleration strokes of minor-road vehicles were significantly reduced, indicating a lower possibility of aggressive driving when the in-vehicle traffic light was applied while considering the waiting time. Meanwhile, an improved steering stability was observed from the driver behaviors at the intersections, as the maximum lateral acceleration of minor-road vehicles significantly decreased when the waiting time was considered., 1. Introduction There are thousands of accidents yearly at priority-controlled unsignalized intersections, which are one of the most common types of unsignalized intersections [1]. We previously proposed an in-vehicle traffic [...]

Advance warning signals are installed upstream of high-speed signalized intersections to warn motorists of impending signal changes. A new advance warning signal design was tested on an approach to a high-speed signalized intersection in Utah that utilized a dynamic blank-out sign with flashers mounted over the roadway. A state-of-the-art evaluation system was installed to collect continuous, nonintrusive data of vehicle speeds and red-light running events. Data were collected prior to and immediately after installation. Cumulative distributions of speed profile data showed statistically significant results after blank-out overhead dynamic advance warning signal (BODAWS) installation evidenced by an increase in mean speeds of 5-10 mph during the green interval, while the system was inactive, followed by a decrease in mean speeds of 5-10 mph after activation of the system. The system also reduced red-light running at the site during the time period immediately after BODAWS installation from five violations per million entering vehicles to one violation per million entering vehicles in the northbound direction, a statistically significant change using logistic regression. DOI 10.1061/(ASCE)0733-947X(2007) 133:10(564) CE Database subject headings: Radar; Traffic safety; Traffic speed; Traffic signals; Intersections.

The study reports on research that evaluated the impact of different types of left-turn phasing on older and younger drivers at high-speed signalized intersections. Using Poisson regression, the likelihood that a driver in a particular age group would be responsible for a left-turn crash under different types of phasing was evaluated. The induced exposure method was used to estimate exposure by age group. The variable of interest was left-turn crash rate for left-turning drivers who were responsible for circumstances contributing to the crash. Older drivers had higher crash rates than younger or middle-aged drivers for all types of phasing. Younger drivers had higher crash rates than middle-aged drivers for all types of phasing. All three age groups had the highest crash rate under protected/permitted and then permitted phasing within their respective age group. DOI: 10.1061/(ASCE)0733-947X(2007)133:10(556) CE Database subject headings: Traffic accidents; Regression analysis; Intersections; Traffic safety; Left-turns; Drive behavior.

Because the prime objective of the current preemption methods for traffic signals located near highway-railroad grade crossings is to clear vehicles from the crossing, secondary objectives such as maximizing pedestrian safety and minimizing vehicle delay are given less consideration and are often ignored completely. Consequently, the state-of-the-practice traffic signal preemption strategies may result in pedestrian safety and efficiency problems at signalized intersections near highway-railroad grade crossings (IHRGCs). The state-of-the-art transition preemption strategy (TPS) algorithm was designed to reduce the probability that pedestrians would be endangered when the standard preemption was initiated by approaching trains. However, there is a possibility of failure because the algorithm is predicated on the assumption that train arrivals can be predicted with certainty. Given the fact that current architecture may not be adequate with respect to safety and efficiency, there is a definite need for research on how to improve traffic signal preemption strategies. In this paper, an improved transition preemption strategy (ITPS) that is specifically designed to improve intersection performance while maintaining or improving the current level of safety is developed. It was concluded that the ITPS algorithm improves the operation of IHRGCs with respect to control delay while simultaneously reducing the probability of pedestrian conflicts associated with the standard preemption method and the TPS algorithm. CE Database subject headings: Traffic signals; Railroad grade crossings; Intersections; Traffic safety.

The impact of left turns on operation is probably the most significant factor in the performance of conventional intersections. As a result engineers have looked to alternative measures for dealing with left turns at intersections to improve performance, some of which have been unconventional schemes. The purpose of this paper is to discuss an unconventional intersection scheme, the upstream signalized crossover (USC), which is a four-legged intersection designed to eliminate left turn opposing conflicts by crossing the left and through traffic to the left side of the road at all four approaches prior to the intersection. The crisscrossing of traffic upstream of the intersection results in four additional secondary signalized intersections. VISSIM was used to model and analyze the unconventional USC intersection as well as a conventional intersection for comparison. The analysis revealed that the USC intersection can handle higher traffic volumes at reduced overall delays. In terms of left turn delay, the conventional intersection performed better at lower volumes. However, the USC was able to handle much higher left turn volumes while maintaining acceptable level of delay. In terms of through movement delay, the USC intersection was found to perform significantly better than the conventional intersection. DOI: 10.1061/(ASCE)0733-947X(2006) (907) CE Database subject headings: Traffic signals; Intersections; Left-turns; Traffic management.

The Highway Capacity Manual (HCM) defines uniform delay as a portion of control delay and estimates it based on the flow diagram originally developed for a protected movement. This paper demonstrates the shortcomings of the HCM delay model in the estimation of uniform delay of permitted left turns from an exclusive lane (PLTEL), and proposes a new uniform delay model developed for PLTEL. The control delays estimated by the original HCM model and the one estimated by the proposed uniform delay model for PLTEL were compared against those from corridor simulation. Results showed that the HCM model tended to underestimate uniform delay, and the proposed model for PLTEL showed improved results. DOI: 10.1061/(ASCE)0733-947X(2006)132:9(708) CE Database subject headings: Traffic signals; Left-turns; Evaluation; Traffic models.

Complete stops at a high-traffic intersection on the campus of a public university were increased with a prompting and consequence intervention. Data were collected at two opposing stop signs (Stop A and Stop B); however, the intervention was implemented only at Stop A. During the intervention, a volunteer stood next to Stop A holding a poster that read, 'Please Stop--I Care,' with 'Thank You For Stopping' on the reverse side. The poster was held by the volunteer so that drivers approaching Stop A could read the sign. Drivers approaching Stop B could see the volunteer but could not read the sign. When vehicles approaching Stop A made a complete stop, the volunteer flashed the 'thank you' side of the poster to the driver. The strategy was evaluated using a multielement design. The intervention increased stops completed at Stop A from a baseline average of 13% to an intervention average of 52%. Stop B also showed improved stopping, from a baseline average of 6% to an intervention average of 28%. Data showed no relation between complete stops made and the drivers' use of turn signals and safety belts. DESCRIPTORS: prompting, complete stopping, safety, antecedent

Abstract: The main object of this study was to design and implement a suitable algorithm and its simulation for an intelligent traffic signal simulator. The system developed is able to [...]

Appendix C of Chap. 16 in the Highway Capacity Manual 2000 (HCM 2000) discusses the method for calculating the left turn factor for permitted left turns. This method uses the queue clearance model, represented by equation C 16-6 of the HCM 2000 to calculate the left-turn factor. This paper reports on a study of the accuracy of this queue clearance model to predict observed clearance times. For this study, queue clearance times were observed for multiple-lane approaches with shared left turns and opposing multiple-lane approaches for five study intersections located throughout Missouri. Data collected at each intersection were used as inputs to the HCM 2000 queue clearance model to predict queue clearance times. A comparison of the predicted queue clearance time and the observed queue clearance time found that the HCM 2000 queue clearance model underestimates observed clearance times on average by 5.8 s. Further research is needed to identify the source of this bias and to recommend improvements to the HCM 2000 model. DOI: 10.1061/(ASCE)0733-947X(2005) 131:12(912) CE Database subject headings: Queueing; Left-turns; Model accuracy; Traffic signals; Traffic management.

In recent years, there has been major interest in 'access management' as a new response to the ubiquitous traffic congestion problem. Among the different access management strategies is the idea of prohibiting left-turn movements at unsignalized driveways. In this study, the Corridor Simulation traffic simulation model was used to evaluate the operational impacts of different left-turn treatments at mid-block intersections on different classes of roadway facilities. The study also examined the impact of varying the arterial and driveway volume on the effectiveness of restricting direct left turns and providing alternative movements. Three different alternatives were considered for left-turn treatments at mid-block unsigualized intersections: (1) no restriction of direct left turns from or to driveways: (2) no direct left turns in or out of driveways and diverted traffic makes a U-turn at the next intersections: and (3) no direct left turns in or out of driveways and diverted traffic makes a U-turn at mid-block. Two additional cases were also evaluated: a jug handle design, and no direct left turns in or out of all-but-one driveways (concentrated left turn). The results show very little operational difference between the no restrictions on direct left turns alternative versus the restrictions with the U-turn alternative movements from site to site. The jughandle design appeared to be a superior alternative for accommodating left-turn deterred traffic for multilane divided and undivided sites compared to mid-block or intersection U-turns. In addition, it is shown that the concentrated left turn appears to be an excellent solution for improving traffic flow conditions. CE Database subject headings: Left-turns; Traffic signals; Intersections; Traffic congestion; Traffic management.

The objective of this research was to determine the safety and effectiveness of selected protected/permissive left-turn (PPLT) signal displays through driver comprehension evaluations. Driver evaluations were conducted using full-scale, fixed-base, fully-interactive driving simulators located at the University of Massachusetts and the Texas Transportation Institute. The PPLT displays were also evaluated in a static environment to provide comparison data. The 12 experimental PPLT signal displays evaluated differed in permissive indication, arrangement, location, and through movement indication. Each PPLT signal display included only the circular green ball and/or flashing yellow arrow permissive indications. Driver comprehension was determined from the distribution of correct and incorrect responses. Findings from the driving simulator study showed a high level of comprehension (91%) with no variation between PPLT displays. The lack of significant differences in driver comprehension is itself a significant finding, indicating the flashing yellow arrow is an alternative to the circular green ball permissive indication. CE Database subject headings: Left-turns; Simulation; Traffic signals; Traffic safety; Driver behavior.

Aiming at the problems of known traffic signal control methods, such as heavy system and huge computation, this paper presents a macroscopic two-dimensional cellular automata (CA) model of an urban traffic signal control system, in which each intersection is regarded as a cell and the flow pressure is treated as the state. The hierarchical control architecture of traffic signal is built. Off the support of the upper level (traffic control center), the lower level (intersection controllers) can implement self-organizing control of traffic signal. The signal decision at an intersection is based on the thought of 'perception-decision.' We establish the simple state perception rule of typical intersection. By means of the computer simulation, the application of CA in signal self-organizing control is proved effective in urban traffic. Index Terms--Cellular automata, perception-decision, rule, self-organizing, signals control.

The research presented in this paper is concerned with modeling the occlusion of ground-mounted traffic signs by heavy vehicles oil multilane highways. It is part of a more extensive research effort to examine the different factors that determine the effect of heavy vehicles oil the visibility of traffic signs. An analytical tool was developed where road geometry, traffic sign, and moving entities are simulated over space at any point in time. This tool dynamically models the movement and location of passenger cars and trucks oil the facility upstream of the subject traffic sign and verifies the continuity of sightline between the subject driver and traffic sign. Besides roadway and sign geometry, the model accounts for other traffic conditions such as traffic level, percentage of trucks, lane utilization, and average speeds of passenger cars and trucks. The occlusion of ground-mounted traffic signs by heavy vehicles is estimated using two measures. The first measure is the probability of a traffic sign being occluded by heavy vehicles under certain traffic and geometric conditions. The second measure estimates the likelihood of a passenger car driver missing the sign based oil the minimum time required for the driver to detect, recognize, and read the message. CAE Database subject headings: Traffic signs; Highways; Visibility; Trucks; Simulation; Transportation models.

The study consists of a systematic simulation evaluation of transit signal priority (TSP) impacts on the operations of a single signalized intersection within a coordinated arterial system. The study demonstrates first that in general TSP provides benefits to transit vehicles that receive priority. Second, TSP has a marginal systemwide impact for low traffic demand, although as the demand increases, so do the systemwide disbenefits of TSP. Third, the systemwide impact of TSP is directly proportional to the frequency of transit vehicles. Fourth, TSP impacts are sensitive to the demand distribution at a signalized intersection. Specifically, transit vehicle arrivals on heavily congested approaches may result in systemwide benefits if the conflicting approaches are not congested. Alternatively, transit vehicle arrivals on lightly congested approaches may produce significant systemwide disbenefits if the conflicting approaches are heavily congested. Fifth, the systemwide benefits of TSP are dependent on the phase at which the transit vehicles arrive, especially if the cycle length is maintained within the priority logic. Sixth, the systemwide benefits of TSP are highly dependent on the optimality of the base signal timings. Finally, transit vehicle dwell times al nearside bus stops can have significant systemwide impacts on the potential benefits of TSP. CE Database subject headings: Traffic signals; Traffic models; Intersections; Sensitivity analysis.

This paper presents an investigation into the different factors that affect sign occlusion by large-dimension vehicles on multilane highway facilities. Parametric analyses were conducted to explore these effects using a simulation model that was developed specifically for this research. The variables investigated involved legibility distance, maximum divergence angle, average speed of passenger cars, relative speed of trucks with respect to passenger cars, lateral offset of traffic sign, number of words in message, traffic level, and percentage of large-dimension vehicles. In general, research results show that the occlusion of ground-mounted traffic signs by larger vehicles is remarkable for conditions that can be described as typical. Also, results suggest that the factors that have most important effect on sign occlusion involve legibility distance, average speed of passenger cars, relative speed of trucks with respect to passenger cars, and number of trucks on the lane of interest. CE Database subject headings: Traffic signs; Visibility; Trucks; Simulation.

Under near-saturated or saturated conditions, the optimal cycle length formulation proposed by Webster becomes infeasible because (1) it generates an unreasonably large cycle length as the intersection critical flow ratio approaches one, and (2) it becomes inapplicable if the intersection critical flow ratio is equal to or greater than one. An attempt is made here to rectify this deficiency by providing a simplistic but reasonably accurate formulation for optimal cycle length under saturated conditions. Using the optimal timing variables obtained based on the delay minimization criterion, the functional relationship between optimal cycle lengths and traffic flow parameters, including intersection critical flow ratio, total lost time, and duration of analysis period, is established through a nonlinear regression analysis. The resulting formulation generates fairly accurate estimates of optimal cycle length with 5.7% average deviation from the analytical solutions. The corresponding average delay, however, only deteriorates about 0.9%. The timing plans consisting of the proposed optimal cycle estimates and the equalized degree-of-saturation green splits produce near-optimal delay performance with 3.3% degradation from the optimal solutions. CE Database subject headings: Traffic signals; Traffic delay; Traffic control; Optimization; Intersections.

This paper presents a gray system theory-based method for the quantitative evaluation and ranking of the operational and safety performance of signalized intersections in urban areas under mixed traffic conditions. Mixed traffic conditions refer to traffic situations in which motor vehicles, bicycles, and pedestrians share a signalized intersection. Such mixed traffic is a typical phenomenon in many cities around the world in which the populations of urban areas are extremely large. Five index parameters are used in the proposed method: the degree of saturation, the average stopped delay, the queue length, the conflict ratio, and the separation ratio. These parameters represent the operational and safety performance of a signalized intersection with mixed traffic. They are inputted into the evaluation equations, which are developed according to the gray system theory. The method is applied to the performance evaluation of the intersections and network in the urban area of Changsha, China. The results show that the method can be used to conduct a comprehensive performance evaluation and ranking of signalized intersections under the mixed traffic conditions that are associated with urban road network systems. CE Database subject headings: Traffic signals; Intersections; Performance evaluation; Urban areas.

In the current Highway Capacity Manual (HCM) 2000, level of service (LOS) is defined as a quality measure describing operational conditions within a traffic stream. It is also stated in the HCM that 'each level of service represents a range of operating conditions and the driver's perception of those conditions.' However, the drivers' perception of traffic operational conditions has not been explicitly considered in defining the LOS categories. This study develops and implements a methodology based on fuzzy clustering to define LOS boundaries based on user perception. The methodology is implemented for determining appropriate LOS categories at signalized intersections. These categories are also compared to the existing HCM 2000 LOS categories. An existing database was used containing user perception-related data on estimated delays and ratings of LOS for signalized intersections, and a fuzzy c-means clustering technique was employed to partition the data sets of the estimated delays and of the quality-of-service ratings into LOS categories. It was found that, based on the fuzzy clustering results, each estimated delay is classified into one major LOS category with one minor LOS category. Conclusions drawn from this study are that (1) users can perceive six levels of service in a fuzzy domain in terms of drivers' time-estimating capabilities; (2) the current HCM LOS categories are appropriate for signalized intersections in terms of category range and number; and (3) revision of the HCM LOS definitions with consideration of fuzzy clustering would accommodate subjective variations and uncertainties in user perception and alleviate the existing concerns related to the rigid LOS boundaries. DOI: 10.1061/(ASCE)0733-947X(2003)129:6(657) CE Database subject headings: Fuzzy sets; Serviceability; Intersections; Traffic signals.

This paper presents the findings of a before-and-after study which evaluated the impacts of installing and operating red light cameras (RLC) at two 'T' and one 'X' signalized intersections. The red running violations and vehicle entry times were gathered before and shortly after RLC installation along each individual approach. After RLC installation, red running violations were substantially reduced by more than 40% at camera approaches but not the case for the opposing noncamera approaches. Overall, there was still an aggregated net reduction of about 7% across all approaches. The RLC was found to be more effective in curbing violations during weekends at camera approaches as well as encouraging red-running violators to speed up and clear the camera approaches more speedily. This had generally resulted in lower entry times of red running vehicles. From the results obtained using generalized linear modeling, it was found that the presence or absence of RLC significantly influenced the after-red times, and lower mean after-red times were observed for camera approaches. In effect, the higher the mean after-red time the higher the rate of red running violations. DOI: 10.1061/(ASCE)0733-947X(2003)129:6(648) CE Database subject headings: Traffic management; Driver behavior; Traffic surveillance; Traffic signals; Traffic safety; Intersections.

Timing plans for coordinated signals are developed online using real-time traffic data collected by detectors or offline using traffic data previously collected but is representative of the period in which the timing plan is to be implemented. The timing plans developed using offline techniques are generally known as time-of-day (TOD) timing plans as they are generally implemented during a specific time of the day. One of the downsides of the TOD timing technique is the handling of coordination parameters--defined by cycle length, phase split, and offset--when one plan is transitioning to the next plan. This paper presents a methodology to optimize traffic flow during the transition period. The methodology, based on dynamic quadratic optimization, achieves synchronization of coordination parameters through an optimum number of cycles and an optimum number of increments (or decrements) of the coordination parameters. The proposed transition period optimization method has the advantage that the user does not need to specify minimum and maximum cycle lengths in the optimization process, as is the case with current methods. Preliminary simulation results that compared the proposed methodology to transition methods embedded in CORSIM showed that it has the potential of reducing queue delay, particularly on minor street approaches. The delays on major street approaches were comparable and similar in both scenarios in which traffic volumes were increasing or decreasing between the succeeding plans. Additional simulation runs involving various scenarios of geometric, traffic, and signalization conditions as well as field evaluation are needed before the efficacy of this method over current methods used in practice can be ascertained. DOI: 10.1061/(ASCE)0733-947X(2003)129:4(392) CE Database subject headings: Optimization; Simulation; Timing; Traffic signals.

The yellow change and red clearance intervals for left-turn movements in right-hand-side driving environments are addressed on an analytic basis. Factors such as safety, perception, comfort, driver's behavior, signal timing, and traffic ordinances are taken into account for setting the intervals. The yellow change interval for left-turn movements is found to be in general longer than that required for straight movements at intersections, because motorists usually slow down before making turns. Moreover, the required red clearance interval is derived in terms of the average curvature of a left-turn curve and the magnitude of acceleration that motorists are willing to bear on the curve. The calculated yellow change and red clearance intervals are in good agreement with the field observations for two signal-controlled intersections. The red clearance intervals in practice are shown to be short in comparison with the field observations and analytic estimates. DOI: 10.1061/(ASCE)0733-947X(2002)128:5(452) CE Database keywords: Left-turns; Traffic signals; Intersections.

To increase the capacity of through traffic at signalized intersections, additional lanes with limited lengths--called auxiliary lanes--are usually added to the roadway at the intersection. Because of their limited length, as well as other factors, these lanes are not fully utilized as other continuous through lanes. The objectives of this research were (1) to identify the level of utilization of auxiliary through lanes added at intersections of four-lane roadways with right-turn driveways and/or side streets present within the downstream length of the auxiliary lane; and (2) to study the effects of auxiliary lane length, right-turn volume exiting downstream into driveways/side streets, and through/right-turn lane group delay on the level of their utilization. Lane-use and right-turning volume data collected during 866 saturated cycles at eight signalized intersections with different auxiliary lane lengths and right-turn volumes were used to accomplish the research objectives. Auxiliary lane length and right-turn volume downstream were found to significantly contribute to the use of auxiliary lanes at the 0.01 level of significance. Lane-use of nearly 0.4-1.9 straight-through vehicles per cycle, depending on lane length and downstream right-turn volume, was observed at the study locations. Though not directly comparable to this study, previous studies had indicated lane-use values within this range. Longer auxiliary lanes and lower downstream right-turn volumes encouraged the use of auxiliary lanes by straight-through vehicles. The range of lane utilization adjustment factors ([f.sub.LU]-factors) calculated from field data was 0.72-0.80, which is lower than the 1997 U.S. Highway Capacity Manual default value of 0.91 for a three-lane through/right-turn group. DOI: 10.1061/(ASCE)0733-947X(2002)128:5(458) CE Database keywords: Intersections; Traffic signals; Traffic volumes; Traffic delay.

This paper demonstrates the feasibility of an advanced concept of traffic control for congested urban arterials in an intelligent transportation system (ITS) setting. The core idea of the new concept is to integrate the capability of dynamic adaptive signals with dynamically optimized time-dependent variable speed. Under such control, speeds would be automatically optimized and set by a central computer in parallel with the other signal control parameters. Speed and signal control parameters would change between links and over time, in response to changing traffic conditions. Drivers would follow the optimized speed as they enter a link. Once an optimal speed has been set for a link, it remains constant until the control cycle ends. Link speeds would be updated only at the end of every control cycle. The control cycle may change in length as system conditions evolve. The new control concept was tested on a congested arterial with multiple links. The arterial system was modeled as a discrete event time varying dynamic system with a control period spanning several cycles. System throughput was maximized subject to such critical operational measures as intersection blockage, queue spillbacks, and other relevant traffic operation measures. Genetic algorithms were used as an optimization tool. Results show that the proposed control concept will significantly improve traffic flow. The new control concept is suitable for on-line implementation in an ITS setting. DOI: 10.1061/(ASCE)0733-947X(2002)128:5(447) CE Database keywords: Intelligent transportation systems; Traffic signals; Traffic speed; Integrated systems.

The stopped delay is a primary factor for measuring the level of service at signalized intersections, and the 1994 Highway Capacity Manual proposed a method for measuring the stopped delay in the field based on direct observation of 'stopped-vehicle counts.' This paper evaluates the expected error in delay measured by this method for various ranges of counting intervals and survey offsets. A mathematical formulation was derived to evaluate this error for different combinations of relevant parameters. Results indicate that the expected error may exceed [+ or -] 100% of the deterministic delay, and significant errors are generally associated with shorter cycles, higher green to cycle ratios, lower degrees of saturation, and longer intervals. Significant errors are also reported when the interval perfectly divides the cycle length. A set of optimum offsets is determined for use with the 20-s interval and different combinations of other parameters. These offsets confine the expected error in the measured stopped delay to be within [+ or -] 1%, a significant improvement regardless of whether the cycle length is divisible by the interval. DOI: 10.1061/(ASCE)0733-947X(2002)128:5(439) CE Database keywords: Traffic signals; Traffic delay; Flow rates.

Highway signs require breakaway base connections. These connections will slip under impact, therefore preventing injuries to the occupants of an impacting vehicle. The breakaway connection works as long as the tension of the bolts is maintained between an allowable range. A method to ensure that the bolts are tensioned to the proper value is presented. It is based on the use of Belleville spring washers. Laboratory and field tests were performed to verify the adequacy of the new method. Seven signs were selected along Florida highways. At each sign, the variations of tension in bolts installed with flat washers and with spring washers were monitored over a period of 1 year. The measurements showed that, at the time of installation, the new method was significantly more effective in ensuring the proper tension in the bolts. Similarly, over the long term, the bolts installed with spring washers maintained the tension in the bolt more effectively and without any loosening. The effectiveness of the breakaway connection with spring washers was also demonstrated during an actual car accident. CE Database keywords: Highway design; Traffic signs; Connections; Experimentation; Florida.

Research describing the use of intelligent agents for real-time, pro-active intersection control in urban traffic is presented. Traffic control systems are dependent on their ability to react to patterns and variances of traffic. The application of autonomous intelligent agents in the control of traffic in urban areas is investigated.

Preemption techniques are designed to provide preferential treatments to buses at signalized intersections. A preemption strategy, if properly designed, can provide continuous green phases to buses at successive intersections, thereby reducing delays and travel times along the bus-street. It can also potentially increase delays and travel times along the cross street. A procedure for economic evaluation of preemption projects is presented in this paper, followed by a case study demonstration. It is a variation of benefit-cost analysis that provides an estimate of the maximum investment that can be justified in a signal preemption project by way of savings in delay, fuel consumption, and emissions. The TRAF-NETSIM model was used to assess the operational consequences of signal preemption. The procedure is found viable and the case study results appear to be reasonable, and sensitive to changes in interest rates and project lives.

A signal timing policy describes operational goals applied when developing a timing plan for a system of coordinated intersections. This research investigates differences in signal timing plans resulting from implementation of five basic signal timing policies (including minimizing delay, minimizing stops, minimizing fuel consumption, maximizing coordination bandwidth, and a 'baseline' policy). Further, this research investigates differences arising from application of different techniques to achieve the same policy goal (e.g., different techniques to maximize coordination bandwidth). Volume and other traffic signal data from four traffic signal systems are collected. Various computer tools including PASSER II-90 and TRANSYT-7F are used to develop signal timing plans that emphasize each policy. For the maximum bandwidth policies, several techniques for achieving the policy goal are applied. In all cases, the resulting signal timing plans are transferred to TRANSYT-7F for comparative simulation of detailed systemwide and route-specific measures of effectiveness. Review of these measures of effectiveness provides insights into the relative success of each timing policy, and the impacts of each policy on route-specific and overall system performance. Based on these insights, general guidelines for application of signal timing tools are proposed.

A vision-based vehicle guidance system for road vehicles can have three main roles: 1) road detection; 2) obstacle detection; and 3) sign recognition. The first two have been studied for many years and with many good results, but traffic sign recognition is a less-studied field. Traffic signs provide drivers with very valuable information about the road, in order to make driving safer and easier. We think that traffic signs must play the same role for autonomous vehicles. They are designed to be easily recognized by human drivers mainly because their color and shapes are very different from natural environments. The algorithm described in this paper takes advantage of these features. It has two main parts. The first one, for the detection, uses color thresholding to segment the image and shape analysis to detect the signs. The second one, for the classification, uses a neural network. Some results from natural scenes are shown. On the other hand, the algorithm is valid to detect other kinds of marks that would tell the mobile robot to perform some task at that place. Index Terms - Advanced driver information systems, color/shape processing, computer vision, neural networks, traffic signs recognition.

The development of a codable model for the design of lane-use and signal-phase control at isolated intersections is valuable especially in developing countries where experienced traffic engineers are scarce. Extensive research concerning the design of signal phases and timing have been conducted in the past while very little has been done for the optimal design of the lane-use or lane-configuration of intersection approaches. However, poor matching of lane-use design and signal-phase design also produces a poor overall result. It is therefore necessary to integrate the design of lane uses and signal phases, and perform the optimization simultaneously. A mixed integer linear programming model is introduced for this purpose. The resultant designs are verified by comparing their performance indices with that of the existing designs as computed by TRANSYT-7E The traffic data used are collected from a selected area of Shenzhen, one of the largest special economic zones of the People's Republic of China. The results indicate significant improvement in minimizing overall delay, stop, and fuel consumption.

The average delay caused to vehicles at signalized intersections is an important criterion in the evaluation of performance at these intersections. Various models have been developed to estimate delay to traffic at signalized intersections. All the models are based on homogeneous traffic conditions; these models may not estimate the delays satisfactorily under heterogeneous traffic conditions. A probabilistic approach based on first-order second-moment method has been adopted to estimate the saturation flow and the delay caused to traffic, at signalized intersections, under heterogeneous traffic conditions. Here, the interaction between the different types of vehicles are incorporated in the modified 1958 Webster model by considering the intercorrelation between different vehicle groups. The input data required for these models and the data required to validate the calculated values were collected by conducting extensive traffic surveys. Results showed that the delay estimated using the probabilistic approach was close to the observed values of delay.

Traffic monitoring and detection systems are important for constructing closed-loop traffic-signal control, freeway-control, and congestion-management systems. Most detection and monitoring systems depend on inductive loops. Recently, many agencies have been investigating video-image-based detection systems because cameras can collect data on several traffic lanes and can be installed quite rapidly on an adjacent pole or bridge. User consensus is that the basic hardware architecture of these systems is well defined. However, there is room for significant improvements in performance and capability of video-detection algorithms. Several researchers are currently working to develop new algorithms. However, due to technology limitations these algorithms have traditionally been evaluated at a macroscopic level by comparing counts obtained by loop detectors with the image-based detection system. This paper discusses the development of a multimedia database-management system for investigating the microscopic performance of video-detection algorithms. The paper describes the process of acquiring the proper data, a definition for a suitable database schema, and the peripheral database clients required to evaluate detection algorithms.

Urban traffic dispatching control using a two-layered hierarchical structure is congruous to large-scale applications. Central dispatching units tackle the upper layer problem of global optimization by performing resource allocation. Local dispatching units approach the lower layer problem of local optimization by performing vehicle routing functions. This dispatching control method is best implemented in large-scale systems because an imbalance decrease is assured. Furthermore, the analytical closed-loop form of the upper layer theory, the procedure for receiving positive integer values and the off-line shifted informational interchange are ideal for real-time implementation.

An experimental infrared optical system was designed to detect and monitor vehicular road traffic. The system used was developed and first tested in the laboratory using infrared laser sources and detectors in conjunction with computerized signal processing and correlation techniques. Preliminary road tests confirmed the system's capability to detect, monitor, and count the passage of vehicular road traffic. It is expected that a system based on the technology described would be cost-effective and weather resistant. Additional developments should give it the potential for more sophisticated applications, including vehicle speed measurement and length classification.

Both stopped and overall delay are useful measures of intersection performance. While stopped delay is easier to measure, overall delay reflects better the efficiency of traffic signal operation. Ratio of overall to stopped delay was assumed to be constant and equal to 1.3 in the 1985 'Highway Capacity Manual.' Recent improvements of the HCM formula were also based on the same assumption. It is demonstrated that for the uniform delay component, the delay ratio is in fact a function of red-period duration and deceleration-acceleration delay. The value of the latter parameter was measured and found to have a mean of 8.6 s. Given this value, the delay ratio is close to 1.3 only for red periods longer than 60 s for random arrivals. For the overflow delay component, the delay ratio depends also on cycle time and degree of saturation. In case of platooned arrivals, the relationship between overall and stopped delay is more complex. This case is analyzed using the step arrival flow model. New equations are proposed for stopped delay as well as for the full and partial stop rates.

The current method of computing the intergreen (yellow plus all-red) interval at signalized intersections assumes that the component variables are deterministic. This paper presents a probabilistic method in which the approach speed, reaction time, deceleration rate, and vehicle length are random variables. The intergreen interval is estimated so that the dilemma zone occurs with a specified probability. A safety margin is defined as the difference between the clearing and stopping distances, which are random variables. Relationships for the mean and standard deviation of the safety margin are developed based on the first-order second-moment analysis. A closed-form solution of the intergreen interval is then derived. The safety margin is assumed to be normal, and this assumption is confirmed. The probabilistic method should be valuable in designing the intergreen interval for any desired reliability level.

The traffic experimental and analytical simulation (TEXAS) model for intersection traffic, version 3.0 was used to simulate actuated signal control and traffic response at a diamond interchange with representative geometric features. Graeco-Latin Square and one-way analysis of variance experimental techniques were applied to investigate the effects of various actuated traffic signal controller settings under three different traffic demand conditions - two symmetrical, and one lopsided. Overall average total delay and stop delay for vehicles traveling through the simulated interchange area were used as the response variables in the statistical analysis and significance testing of data obtained from more than 2,500 runs of the TEXAS model. Results indicated that the settings of the timers that determine clearance-green, green-split, and end-of-maximum intervals on actuated diamond-interchange signal controllers were sensitive to both intersection geometry and traffic demand and played a significant role in defining the optimum controller settings when implementing a three-phase, lag-lag phase-sequence pattern. Findings from the study of a four-phase-with-two-overlaps, lead-lead phasing pattern indicated that the advanced green timer and the internal detector logic were the only controller settings that had a significant effect on traffic performance for the conditions studied. The TEXAS model, version 3.0 is a powerful new analysis tool for determining the best signal timing at individual diamond interchanges operating under specific traffic, geometry, and control conditions; this study illustrates its application., The effects of traffic signal control at diamond interchanges is studied using the traffic experimental and analytical simulation model. Results show that in the three-phase phasing pattern, the setting of clearance-green, green-split and end-of-maximum timers depend on the intersection geometry and traffic demand. In the four-phase overlap phasing pattern, advanced green timing and internal detector logics were found to affect traffic demand. The three-phase control is also more efficient than the four-phase overlap control for accurate signal settings at certain interchange geometries.