Thomas Urbanik

Development and Evaluation of Intelligent Bus Priority Concept

Development and laboratory testing of an intelligent concept for providing priority to buses at signalized intersections without disrupting progression are discussed. The concept used bus position information to predict when in the cycle a bus would arrive at the bus stop and stop line of a signalized intersection and to determine whether a bus needs priority. The strategy used to provide priority was selected on the basis of the estimated arrival time of the bus at the stop line. Priority was provided by using phase extension, phase insertion, and early return strategies without causing the controller to drop from coordination. Implementation of the strategies was accomplished through normal traffic-signal controller commands (such as Ring Force Offs and Phase Holds). Hardware-in-the-loop simulation studies were performed to evaluate the effectiveness of the concept with real traffic-signal controllers. The performance of the intelligent bus priority approach was examined at three volume-to-capacity levels: 0.5, 0.8, and 0.95. Significant reductions in bus travel times were achieved at all three volume-to-capacity levels by using the intelligent bus priority approach. Use of the intelligent bus priority approach resulted in only minor increases in total system stop delay and individual approach stop delays at volume-to-capacity levels of 0.5 and 0.8. The results of the simulation studies performed as part of this study suggested to the researchers that the intelligent bus priority approach could be used at moderate traffic levels (up to volume-to-capacity levels of 0.9 or less) without significantly affecting cross-street delays.

VARIATIONS IN CAPACITY AND DELAY ESTIMATES FROM MICROSCOPIC TRAFFIC SIMULATION MODELS

One of the issues involved in using microscopic simulation models is the variation in the simulation results. This study examined some of the more popular microscopic traffic simulation models, CORSIM, SimTraffic, and VISSIM, and investigated the variations in the performance measures generated by these models. The study focused on the capacity and delay estimates at a signalized intersection. The effects of link length, speed, and vehicle headway generation distribution were also investigated. With regard to variations in performance measures, the study found that CORSIM yields the lowest variations, whereas SimTraffic yields the highest. The highest variation in each simulation model normally occurs when the traffic demand approaches capacity. It was also found that delays are affected by the link length and speed in simulation models. Such an impact on delays is closely related to the range of speed variations. In general, shorter links and higher link speeds result in lower delays. There is no strong evidence that the headway distribution used to generate vehicles in the simulated network has any effect on capacity and delay estimates. Multiple simulation runs are necessary to achieve an accurate estimate on the true system performance measures. With a 10% error range in estimated delay, two to five runs may be enough for under-capacity conditions, but more than 40 multiple runs may be necessary to accurately estimate delay at, near, or over capacity.

Another View of Truck Lane Restrictions

As truck volumes on U.S. highways continue to increase, both elected officials and members of the general public often look to the use of lane restrictions for large trucks as a means to increase operating efficiency and highway safety. In the past, research has offered little evidence that either safety or efficiency is positively affected by widespread use of this practice. Another view of truck lane-use restrictions on high-speed, limited-access facilities is offered. To determine the effects of lane-use restrictions, scenarios that varied traffic characteristics such as volume, grade, percentage of trucks, and the presence of entrance and exit ramps were developed with the VISSIM model. In each scenario traffic along the model freeway segment was monitored to determine the effect of the lane-use restrictions by comparing values of various traffic measures from a model run first without and then again with truck lane restrictions. As in past research efforts, the implementation of truck lane restrictions in a variety of scenarios is shown to have little effect on a number of traditional measures, including average speed, speed differential between cars and large trucks, and level of service. However, further examination of data resulting from the simulation process shows that significant gains in the area of safety and driver comfort may be realized through the reduction of lane-changing maneuvers by all vehicle types, lending support to past driver surveys indicating strong support for this practice among drivers of passenger vehicles.

Pedestrian Timing Alternatives and Impacts on Coordinated Signal Systems Under Split-Phasing Operations

Split phasing can sometimes be more efficient in serving vehicular traffic under certain geometric and traffic flow conditions, such as the case in which a high volume of left-turning traffic is served from a sharedlane configuration. However, pedestrian crossing-time requirements can have a significant impact on intersection operations, especially in coordinated signal systems. Various alternatives for providing pedestrian timings under split-phasing operations are presented. The advantages and disadvantages, implementation strategies, and potential impact on intersection operations, especially on coordinated signal systems, are addressed with regard to each timing alternative. Further, the concept of the two-stage crossing design and the use of an exclusive pedestrian phase under split-phasing operations are investigated. The proposed model can be used to determine when exclusive pedestrian phasing can actually improve operational efficiency.

The areawide real-time traffic control (ARTC) system: a new traffic control concept

A traffic control system, called areawide real-time traffic control (ARTC), that addresses frequent occurrences of congestion and provides areawide traffic progression is presented. The signal controllers in ARTC are interconnected through a computer network. By exchanging traffic flow information among the signal controllers, ARTC provides a new concept in areawide traffic control. With a global view of the traffic in the area, ARTC anticipates congestion. Simulation results of the ARTC prototype control algorithm over a linear road topology are also presented, and the results show significant improvement over an optimized fixed time control. The signal controllers and the computer network are designed to support the real-time communication requirements and a sufficient level of fault tolerance. >

EVALUATION OF DIAMOND INTERCHANGE SIGNAL CONTROLLER SETTINGS BY USING HARDWARE-IN-THE-LOOP SIMULATION

Research sponsored by the Texas A&M University ITS Research Center of Excellence was used to analyze the application of hardware-in-the-loop simulation at a diamond interchange. The study shows that hardware-in-the-loop simulation can improve the accuracy of traffic operations analysis by removing the inherent differences between emulated controllers and the actual hardware. In this study, a controller enhancement called conditional service was considered for implementation at an actuated diamond interchange. An evaluation of the traffic operations at the diamond interchange was completed using PASSER III-98, CORSIM, and hardware-in-the-loop simulation. The results of these analyses were compared to field observations that were used as the basis for evaluating the accuracy of each of these methods. An assessment of each method was discussed to identify issues and results using each method. One of the important supplementary benefits of hardware-in-the-loop simulation is that it allows engineers and technicians to test signal control strategies and hardware before deployment in the field. This capability provides a platform for innovation and the development of new control strategies. Hardware-in-the-loop simulation is also a valuable training tool.

DETECTION RANGE SETTING METHODOLOGY FOR SIGNAL PRIORITY

In urban areas, traffic signals often cause significant amount of delays to transit vehicles. The article discusses the potential to reduce control delay caused by traffic signals by implementing signal priority. Engineering studies are necessary to address both traffic and transit signal operations before the systems can be implemented. A comprehensive program requires coordination between the transit agency and the applicable transportation department to address needs of both agencies and users. The article details the efforts of the City of Portland and the Tri-County Metropolitan Transportation District of Oregon as well as the methodology for signal timing and detection distance setting.

VALIDATION OF PHOTOMETRIC MODELING TECHNIQUES FOR RETROREFLECTIVE TRAFFIC SIGNS

Recent research in the United States has focused on the development of minimum retroreflectivity levels for traffic signs. The engineered approach uses a supply luminance versus demand luminance concept to achieve a metric that can be used to set minimum retroreflectivity levels. The supply luminance depends on reliable modeled estimates of headlamp illuminance reaching traffic signs and the resultant luminance directed back toward the driver. While the science behind the photometric modeling process is fundamentally sound, a small pocket of literature shows inconsistent relationships between measured and modeled illuminance and luminance levels. A systematic validation study of photometric modeling was done with field measurements made under conditions identical to those that were modeled. A set of headlamps were photometrically measured along with three different samples of retroreflective sign sheeting materials. Illuminance and luminance levels were then modeled for nine sign positions and three vehicle types. Then field illuminance and luminance were measured using the same scenarios, headlamps, and retroreflective sign sheeting materials. The field measurements were recorded once on a concrete pavement and once on an asphalt pavement. Both sets of field measurements also included baffled and unbaffled measurements so the impact of pavement reflection could be considered. Photometric modeling techniques of nighttime traffic sign performance compared well with field measurements made under identical conditions. The maximum illuminance difference was 16% and was attributed to the pavement reflection properties. The maximum luminance difference was only 2.4%. The retroreflective performance of traffic signs redirects most of the pavement reflection back toward the pavement. Therefore, estimates and measurements of luminance are less affected than illuminance.

The advanced distributed ramp metering system (ARMS)

Ramp metering is an important technique to effectively utilize the freeway capacity by regulating the traffic flow of freeway entrance ramps. In this extended abstract, we discuss the outline of the free flow control algorithm of the Advanced distributed Ramp Metering System, ARMS, for the real-time control of freeway ramp metering systems. ARMS consists of three levels of control algorithms integrated together for free flow control, breakdown prediction, and congestion resolution. Based on a free flow traffic model, the free flow control algorithm takes into account of the congestion risk when it tries to maximize the traffic throughput. The breakdown prediction algorithm can make prediction on the possibility of imminent congestion caused by flow breakdown, and the congestion resolution algorithm is to resolve the congestion if it actually occurs. The ARMS has a modular architecture so that it can be scaled for incremental implementation. To control freeway traffic, a system wide optimization objective is first defined for a target area. Then, ramp metering decisions are made by the entrance ramp controllers within the target area after their traffic data are exchanged.<<ETX>>

Secondary Coordination at Closely Spaced Actuated Traffic Signals

This paper presents a method of addressing stochastic variation at closely spaced signalized intersections to provide secondary coordination to “minor” movements with significant traffic volumes. A neurofuzzy signal control system was designed in this study to manage a noncoordinated movement to avoid queue spillback. Building on the conventional actuated-coordinated control system, the neurofuzzy controller does not lose the benefit of the primary coordination of the conventional controller but establishes a “secondary coordination” between the upstream coordinated phase (through phase) and the downstream noncoordinated phase (left-turn phase) on the basis of a real-time traffic demand. Under the neurofuzzy signal control, the traffic from the upstream intersection can arrive and join the queue at the downstream left-turn lane and be served in a timely fashion and thus reduce the likelihood of being delayed at the downstream intersection. The simulation results indicate that the neurofuzzy signal control...