A more definitive understanding of capacity and level of service (LOS) at intersections with actuated controllers was needed to properly analyze their performance. The current version of Chapter 9 of the 1985 Highway Capacity Manual
(HCM) has a number of shortcomings that needed to be addressed.
The objective of this research was to develop a capacity and LOS analysis methodology for intersections with actuated control that can augment or replace the existing procedures in HCM Chapter 9.
Research included the following tasks: (1) Review current practices used by the traffic engineering community for design and analysis of capacity at actuated intersections, and review the state of the art of analytical, empirical, and simulation/optimization-based analysis procedures. (2) Develop a preliminary methodology that can assess the capacity and LOS performance of individual actuated intersections. Identify key design and operational parameters; recommend measures of effectiveness (MOEs) to be employed, including delay; explain the rationale for the methodology's use; and provide examples of its application using existing field data or simulation/optimization models, or both. (3) Assess the preliminary methodology developed in Task 2 by applying it to existing field data, augmented as necessary by data derived from simulation/optimization models. Revise the methodology as needed in response to the findings from this effort, and develop a plan for the pilot study (see Task 5) that will further calibrate and validate the methodology. (4) Prepare an interim report presenting the results of Tasks 1 through 3 and the plan for the pilot studies of Task 5. (5) Conduct pilot studies for a minimum of two conditions--fully actuated (isolated) and semiactuated (coordinated, e.g., as part of a network)--possibly at the same site. As part of this pilot study, assess the methodology's performance based on these new field data, and evaluate the adequacy of the data-collection plan. (6) Revise and expand the pilot study plan to include additional sites and data-collection efforts for the analysis of a limited number of typical traffic-actuated intersection conditions. The plan must include the ability to measure and validate all key model assumptions, parameters, and performance measures. (7) Collect data according to the plan developed in Task 4 and revised in Task 6. Data shall be collected under good weather conditions, at times not hampered by nonrecurring congestion, and under volume conditions that will allow assessment of a range of levels of service. Simulation/optimization models can be used to supplement the field data collected where gaps are identified. (8) Reduce and analyze the data collected in Task 7, and further calibrate, validate, enhance, and document the methodology. (9) Prepare a detailed final report describing the form, content, and rationale for the recommended capacity and LOS analysis procedures. The main report should document how the methodology should be applied, where it can be applied, and the accuracy of its MOE predictions. One appendix should indicate modifications to the existing HCM Chapter 9 that would be required to implement the methodology developed, and a second should provide the draft of a new Appendix II for HCM Chapter 9 that explains the methodology and its use.
: The revised final report has been received and some of the results were incorporated into the 1997 revision to the HCM. Additional results were incorporated into the year 2000 HCM.
The agency final report is available for viewing through this link: NCHRP Web Document 10: Capacity Analysis of Traffic-Actuated Intersections: Final Report (1996)