This research had two equally important objectives: (A) development of techniques to measure the performance of automobile traffic on urban streets for real-time applications and (B) development of procedures to predict the performance of automobile traffic on urban streets that will provide a foundation for an update of the HCM.
The results from the work done on Objective B were incorporated into the HCM 2010 and the contractor's final report is available in Volume 4.
NCHRP continuation funds ($225,000) were approved to further the work done on Objective A. This was being carried out under NCHRP Project 03-79A and the results of this project will be included in that report.
NCHRP Project 3-70, Multimodal Level of Service Analysis for Urban Streets, is examining the attributes of the facility that influence travelers' perception of their trips. Many candidate attributes have been identified for each mode of travel, including ones related to the design, operation, and maintenance of the street. For the automobile mode, operational attributes being investigated include average speed, number of stops, total delay, and queue length. Work is underway now to assess the importance of each of the attributes to travelers.
Transportation agencies typically operate traffic signal systems to minimize some combination of delay, stops, and queues. Directly measuring the performance of the system in real time has not been practical, but recent advances in detector and controller technologies now make it conceivable. Real-time knowledge of system performance should enable transportation agencies to improve their capabilities in several real-time applications (e.g., adaptive traffic control, traveler information, incident management, and system performance monitoring).
The Highway Capacity Manual (HCM) is commonly used for planning and designing urban streets, and travel speed is used to determine the level of service for automobiles. Although the results of NCHRP Project 3-70 may change that, travel speed will probably continue to play a large role. The HCM procedure for predicting travel speeds has weaknesses, particularly in the determination of the free-flow speed and failure to fully account for some factors that influence travel speed, including arterial traffic volume, signal offset, access point density, cross-section design, arterial weaving, and platoon dispersion.
This research project uses the HCM term "urban street" although it is expected that the research results will be applicable to a broad range of interrupted-flow arterial and collector roads in urban, suburban, and rural settings.
The task framework is based on separate, concurrent tracks for Objectives A and B, because their final products and the paths to those products are different. It is expected, however, that insights gained in the pursuit of Objective A will be beneficial to the work for Objective B and vice versa.
Objective A, Measurement for Real-Time Applications
Task A.1. Review literature and websites for information on technologies and techniques for measuring and monitoring automobile performance on urban streets in real time, particularly such aspects of performance as travel times, speeds, and queues.
Task A.2. Describe how performance information could be used in real-time applications and the likely benefits.
Task A.3. Describe and discuss promising techniques for measuring the performance of automobile traffic on urban streets, including data requirements, processing needs, accuracy of measurements, and limitations. Assess the feasibility, practicality, and cost-effectiveness of these techniques. Develop a detailed plan for conducting Tasks A.5 and A.6 for a limited number of techniques commensurate with the resources available, outlining the issues associated with using simulation models and how they will be addressed.
Task A.4. Within 9 months of the contract start date, submit an interim report presenting the results of Tasks A.1 through A.3.
Task A.5. Develop techniques for measuring and monitoring the performance of automobile traffic on urban streets in real time. This may require new algorithms that relate available traffic detector data to traffic flow performance.
Task A.6. Evaluate and refine the techniques developed in Task A.5 using simulation models and field data. Develop fully detailed descriptions of techniques, including functional requirements, flow charts, and pseudo-code. Define the benefits of their use in real-time applications developed in Task A.2.
Task A.7. Develop an implementation plan for transportation agencies to use in incorporating the results of this research into practice.
Task A.8. Submit a final report that documents the entire research effort.
Objective B, Prediction for the Highway Capacity Manual
Task B.1. Review, describe, and critique pertinent literature on predicting the performance of automobile traffic on urban streets.
Task B.2. Based largely on the work done in NCHRP Project 3-70, list performance measures for automobile traffic and identify the key measures that should be addressed in this project. After approval of the key measures by the project oversight panel, review existing methods for predicting those measures and identify their strengths and weaknesses.
Task B.3. Propose and discuss improved analytical approaches for predicting the key performance measures. Recommend a preferred approach for each key performance measure and identify field-data needs and sources to develop the approaches into prediction procedures for the HCM. Develop a detailed data-collection and analysis plan.
Task B.4. Within 9 months of the contract start date, submit an interim report presenting the results of Tasks B.1 through B.3.
Task B.5. Execute the approved data-collection and analysis plan.
Task B.6. Refine the recommended approaches into analytical procedures. Demonstrate the procedures' advantages in predicting the key performance measures. The procedures should be clear and rational and the input data should be reasonably accessible to practitioners.
Task B.7. Develop a computational engine in a convenient format that replicates the computations of the procedures developed in Task B.6 and that can be used by software developers of highway-capacity-related packages.
Task B.8. Rewrite relevant portions of Chapter 15, "Urban Streets," suitable for inclusion in the HCM, including example problems and any necessary appendices. Identify other sections of the HCM affected by the changes in the chapter.
Task B.9. Submit a final report that documents the entire research effort and includes the Task B.8 text as a stand-alone appendix and the Task B.7 engine on a CD-ROM.