AGENDA #5a
MEMORANDUM
TO: Mayor and Town Council
FROM: W. Calvin Horton, Town Manager
SUBJECT: Report on Intersection Traffic Signal Timing During Peak Hours
DATE: June 11, 2001
This report responds to the traffic signal timing element of the following Town Council adopted goal for 2001:
Adopted Goal: Study timing of signals at intersections at peak hours. Assess feasibility and utility of putting transponders on buses so that they could receive priority at intersections.
We are preparing a report that will be presented to the Council in the fall regarding the utility and feasibility of using bus transponders in Chapel Hill.
With technical and funding assistance from the North Carolina Department of Transportation, the traffic signal system serving Chapel Hill and Carrboro was upgraded in 1994. This upgrade involved approximately 60 intersections, and included replacement and/or installation of traffic signal heads, cabinets, controllers, communication cable, vehicle detector loops, remote communication units, and computers necessary to create our present computerized traffic signal system that has now grown to include approximately 90 intersections.
One of the primary objectives of the system upgrade was to more effectively utilize the traffic signals by interconnecting previously independent intersections, thereby allowing signal timing coordination along major travel corridors. The upgrade also made it possible for Town staff to use computers to monitor and manipulate signal timing plans for maximum efficiency.
Town and State technical staff meet routinely to evaluate and adjust traffic signal operations to optimize service under all conditions, including peak traffic periods. A variety of techniques are used with our system, including variable timing plans based on time of day, demand responsive signal timing, and coordinated signal timing at intersections along a given travel corridor. We are also presently testing the use of video cameras to monitor real-time traffic conditions and to automatically adjust traffic signal operations accordingly. Video cameras have been installed at the intersections of NC-54/Meadowmont Lane and US 15-501/Culbreth Road, and we are now in the process of adjusting them for proper operation.
Last fall, we initiated a comprehensive evaluation of the timing plans for the entire signal system. We determined that many timing plans installed and operating at intersections did not match the design plans in our system records. We discussed this with the State, and were provided with technical assistance to analyze and readjust timing plans as necessary to improve overall system efficiency and effectiveness. We have completed traffic signal adjustments on most of the major arterial corridors serving Chapel Hill and Carrboro, and those signals are coordinated wherever possible. Significant effort has been and continues to be focused on the US 15-501 corridors on the east and south sides of Town, the NC 54 corridor on the east side of Town, and the NC 86 corridor on the north side of Town.
We are now working on analyzing and adjusting traffic signal timings at localized intersections within Chapel Hill and Carrboro. Timing and equipment improvements have been completed at downtown intersections in both communities, and we are continuing to work through the entire inventory of signalized intersections system-wide.
It is our objective to use the signal system to provide the highest possible level of service at all intersections at all times of day. We particularly focus on morning, midday, and evening peak hour travel periods when traffic volume is typically the highest and congestion the worst. The traffic signal system is computer and manually manipulated to do the best possible job under constantly varying traffic conditions. This does not eliminate congestion entirely, but it does mitigate it to the maximum extent possible.
Because our system is beginning to show signs of aging, we are experiencing mechanical and electrical problems with increasing frequency. These problems typically involve broken or short-circuited vehicle detector loops at intersection approaches, electrical faults in the communication cables between signal controllers and communication units, and obsolete controllers. When these problems occur, traffic signal operations are affected and congestion typically increases until we are able to make the necessary repairs.
Drivers usually call in problems as they occur, and we make adjustments remotely via our computer system or send a technician to the site to perform the necessary adjustment or repair. Most repairs can be accomplished within a day or two. However, if repairs require the use of contract services, significant delays often occur because we are subject to the contractor’s schedule. We commonly experience difficulties in getting prompt repairs to vehicle detector systems because this work is done by a contractor, not by Town forces.
We have initiated discussions with the North Carolina Department of Transportation regarding another comprehensive traffic signal system upgrade in the near future. This upgrade would include state-of-the-art controllers and fiber optic communication cables, which we would expect to result in a more efficient and reliable system.
Town and State staff are continuously working on getting the best possible performance from our traffic signal system at all times of day and night, including peak periods. We regularly monitor and evaluate all traffic signal locations in Chapel Hill and Carrboro for proper operation. In most cases, problems associated with our traffic signal system operations can be traced to equipment malfunctions or failures. We are working with the State to obtain funding to upgrade our traffic signal system, including replacement of worn out and obsolete equipment and communication lines. We hope to complete that work within the next 5-6 years, depending on the level of State assistance we can negotiate.
1. Signal System Map