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Benefits of Retiming Traffic Signals, The
Institute of Transportation Engineers. ITE Journal, Apr 2004 by Sunkari, Srinivasa
Local counties and municipalities that have responsibility for the operation of signals within their jurisdictions also may time traffic signals. Usually, this is performed within an agency's public works or traffic engineering department, depending on the depth of staff available within the agency.
In today's environment of limited public resources and reduced staffing, many agencies are using the services of consulting engineers to perform signal timing projects. This is particularly applicable to periodic timing applications funded by grants or special funding opportunities.
Political bodies, planning organizations and other advisory committees help drive the signal timing process indirectly by authorizing funding for signal timing studies and related improvements.
In addition, the public is involved as a user and as an affected party. Signal timing complaints and requests often are received from the motoring public with requests to update studies or make signal timing improvements.
WHAT ARE THE CONSTRAINTS OF OPTIMIZING AND OPERATING TRAFFIC SIGNALS?
Many factors limit the extent to which intersection efficiency can be improved with the optimization of signal timing. Although they are interrelated, these factors, or constraints, can be broken into three general categories: institutional, physical and temporal.
Institutional constraints on signal timing optimization pertain to the allocation of resources within an organization or agency and the relationship agencies have across jurisdictional boundaries. Competing budgetary demands within an agency may mean that insufficient resources (in terms of staff time and/or outsourcing contracts) are available to perform the data collection, analysis and implementation necessary for proper signal operation, timing and maintenance.
In arterial environments where multiple agencies are involved, a lack of cooperative working arrangements may produce inconsistent operation. Separate agencies also may place different priorities on signal control or may face equipment incompatibilities that limit the extent to which signal interconnection can be accomplished.
Across and within agencies, a local political climate may exist that does not favor optimal signal and arterial operation. For example, an agency may be willing to accept non-optimal signal operation to increase real and/or perceived safety along an arterial corridor.
Physical constraints are geometric barriers to more efficient signal operation. The more obvious examples of physical barriers include turn pockets of insufficient length, a lack of necessary turn pockets, or too few primary lanes for servicing traffic demand (lack of capacity). In such cases, green time allocation at a signal may be used to attempt to compensate for the limiting geometric feature(s).
Irregular and/or close signal spacing also have a detrimental effect on signal efficiency, in that poor spacing places artificial restrictions on the amount of green time available for a platoon of vehicles to move from one intersection to the next without stopping. Also, mid-block access points may contribute enough traffic to the arterial to interfere with progression between intersections.
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