Defining Design Space for Parameters of Traffic Signal Timing: Empirical Approach

Abstract

This paper proposes an agile, scalable approach for an agency to use for defining a design space for parameters of traffic signal controllers that reflect the agency's procedures. This design space is more commonly known as a checklist of parameters that must be configured in a controller database. The procedure for establishing this design space used simple network-monitoring protocol messages from programmed traffic signal controllers to traverse the controller database tree systematically with the get-next command that was available on controllers that supported the National Transportation Communications for Intelligent Transportation System Protocol (NTCIP). In the case study, a corridor of 22 intersections (five isolated and 17 coordinated) was analyzed to establish the design space empirically. The controllers that were studied had approximately 74,000 configurable parameters, although many of these are seldom configured by most agencies. Longitudinally along a five-intersection corridor, approximately 430 parameters (0.6%) on isolated intersections were changed. Longitudinally along a 17-intersection coordinated system, approximately 1,700 parameters (2.2%) were changed. Approximately 93% of the parameters that were changed on the isolated intersections were defined by NTCIP 1202. Only 28% of the parameters that were changed on the coordinated intersections were defined by NTCIP 1202; the remaining 72% were vendor specific. The paper concludes with a series of tables that summarize the broad spectrum of parameters to be configured for a modern traffic signal controller to operate properly. Agencies can use these tables as a checklist for defining expectations precisely when individuals develop new traffic signal controller configurations or update existing ones. Similarly, consultants can use these tables and procedures to define a clear scope of work on signal-timing projects.