William C. Taylor

ANALYSIS OF INTERSECTION DELAY UNDER REAL-TIME ADAPTIVE SIGNAL CONTROL

The United States Department of Transportation has recently begun implementation of the national demonstration project for suburban Advanced Traffic Management Systems (ATMS) utilizing the Sydney Coordinated Adaptive Traffic System (SCATS). SCATS is an automated, real time, traffic responsive signal control strategy. The expected benefit from the system comes from its ability to constantly modify signal timing patterns to most effectively accommodate changing traffic conditions. The objectives of this research study were to analyze the differences in certain delay parameters which would occur as a result of implementing SCATS signal control. The study employed a macroscopic simulation procedure to compute intersection delay under both a strategy that changed signal timings once per hour and SCATS signal control. A comparison of delay under both forms of control is presented. The study findings demonstrated mixed results regarding the benefit of SCATS control. A general conclusion of the study was that SCATS distributed the delay across competing approaches more evenly. However, in some cases this resulted in an increase in the total intersection delay. The observed delay change was attributed primarily to the saturation equalization objective of the SCATS control program. SCATS attempts to allocate green time to the intersection approaches based on the degree of saturation. Under this philosophy the system is able to balance the percentage of green time between all approaches, resulting in more uniform delay.

Evaluation of Bus Priority Signal Strategies in Ann Arbor, Michigan

With the emergence of intelligent transportation system technologies there has been a renewed interest in the bus priority signal (BPS). The effect of providing the BPS treatment on the Washtenaw Avenue Corridor in Ann Arbor, Michigan, was studied. The NETSIM graphic animation feature was used to detect the bus arrival and award preemption. The signal timing plan was then restored to the original signal setting in subsequent cycles. The model was calibrated using field data, and the sensitivity of the model to several variables was tested. The corridors signal timing was first optimized using the TRANSYT-7F model. The green extension and red truncation with and without compensation, the skip phase with and without compensation, and the conditional preemption plans were evaluated. It was found that in all cases signal preemption disrupts traffic progression and, thus, increases overall vehicle delay. The results of preemption were analyzed at each intersection as well as over the entire simulation network. The most appropriate preemption strategy for each intersection was determined and used in the simulation. Bus travel time and delay were reduced when this optimal BPS plan was used.

Effect of Continuous Shoulder Rumble Strips and Pavement Marking on Lateral Placement of Vehicles

Shoulder rumble strips and enhanced pavement markings were two key areas identified by AASHTO to reduce run-off-road collisions. The Michigan Department of Transportation is currently testing the effectiveness of placing shoulder rumble strips close to the edge of travel lanes and painting a line on the rumble strip to improve the retroreflective properties of the line. Two issues arise from placing the rumble strips closer to the edge line and moving the paint line onto the rumble strip: the potential increased noise when vehicles crossed over the rumble strips and damage to the pavement if vehicles moved closer to the construction joint between the travel lane and the shoulder. This study found that simply moving the paint line onto the rumble strips resulted in vehicles moving slightly closer to the edge of the travel lane. However, maintaining the current edge line and adding an additional paint line on the rumble strip resulted in vehicles moving away from the edge of the pavement and thus reduced no...

EVALUATION OF MICHIGAN 70-MPH SPEED LIMIT

On August 1, 1996, the speed limit on certain sections of Michigan freeways increased from 104.6 to 112.6 km/h (65 to 70 mph). This was due to the Michigan Legislature passing a bill that permitted the governor of Michigan to increase the speed limit given that a study be conducted to determine the effects on safety and capacity. Michigan State University conducted the study that determined the effects of increasing the speed limit on certain sections of highway. This study examined not only freeways that were increased to 112.6 km/h (70 mph), but also the speeds and capacities of freeway sections where the speed limit was not increased. Different types of speed analyses were done in comparing the test sections where the speed limits were raised with the control sections where the speed limits were not raised. The analysis also included categorizing the roadway into intercity and recreational routes to determine the effect on speeds for different uses in road use. The speed data also were broken down into different vehicle types. A preliminary accident analysis was performed on the control and test sections to determine the effect of increasing the speed limit on accidents. It was proved that increasing the speed limit on certain sections of freeway in Michigan had little effect on the change in speed and capacity on both test and control sections.

Effect on Crashes After Construction of Directional Median Crossovers

The purpose was to determine the safety impact of a program to replace bidirectional median crossovers with directional median crossovers on urban arterials. The state of Michigan has adopted this strategy to increase safety and reduce operational problems associated with the lack of storage space in bidirectional median crossovers. Eight arterial road segments were studied, varying in length from 1.17 km to 8.91 km, in which this change had been made. A total of 54 bidirectional median crossovers were replaced on these eight segments. The crash analysis showed an average of over 30 percent reduction in both total crashes and crashes involving at least one injured party. This reduction occurred almost exclusively at the locations in which the bidirectional median crossovers were replaced, with no significant change observed at crossovers that were not changed.

Application of a Dynamic Model for Arterial Street Incident Detection

Existing freeway and signalized arterial street incident detection algorithms were investigated to determine their merit for use on urban arterial streets. Based on this investigation, a Kalman filtering algorithm was modified to recursively filter and update aggregate traffic flow and speed data to estimate true values. A test using measured arterial street data at a signalized intersection shows good tracking ability on these traffic variables over time. A test using data from an incident on an arterial street also confirmed that this algorithm has good potential for arterial street incident detection.

A vision-based vehicle matching system

This paper describes a machine vision system that is able to match vehicles based on their color and shape (edge) attributes. The matching results enable the authors to estimate the travel time between two points on a road network. The system was tested on real video data that was collected in Michigan. The authors show that the travel time estimates obtained by their vision system are comparable to results that were obtained by a manual review of the video tapes.