Traffic Signal Design
Gorove Slade works closely with state and local transportation agency staff in the initial phases of traffic signal project planning to identify the critical design elements. Often, this includes the identification of right of way or utility constraints, identification of intended signal equipment and appropriate coordination with adjacent signals, appropriate pavement marking plans, and an overall traffic signal design network.
Five tasks constitute a typical work program for assessing and satisfying the traffic control needs of an intersection:
- Signal Warrant Data Collection and Analysis- 24-hour daily traffic volumes at the intersection are collected, and a Traffic Signal Warrant Analysis report for the intersection is prepared using the most recent projected traffic at the intersection.
- Field Survey- The first step is the acquisition of a field survey and/or approved intersection design plan. Next is the conduct of a right of way survey of the roadway and a topographic survey of the area of the proposed signalization. Subsurface utility mapping is often performed in conjunction with the topographic survey.
- Traffic Signal Design- The design process proceeds in two phases: the preliminary plan and the final plan. Preliminary signal plans show the traffic signal support system, location of signal heads, lane geometry, phasing diagram, crosswalks, handicap ramps, sidewalks, ground-mounted, and overhead mounted traffic control signs, right of way lines, and existing and proposed utilities. Preliminary signal plan submission can be prepared in three to four weeks. Once the preliminary signal plan is approved (and approval times vary greatly), we prepare a final signal plan that will show all necessary vehicular detectors, conduit and cable runs, color sequence chart, initial timing chart, and all general notes. Our final design submittal will be prepared approximately two (2) weeks from the date of the approval of the Preliminary Signal Plans.
- Pavement Marking & Signing Plan- A pavement marking and signing plan are prepared to accompany the final signal design. This plan will identify existing, existing to be removed, and proposed lane markings and ground-mounted signage on the approaches to the signal. Typically, the extents of this plan include the beginning of turn lane tapers to the middle of the intersection.
- Traffic Signal Timings- Once the final signal plan is approved, we complete the final phase of the signal design process. The final submittal will incorporate signal timing analysis. A Synchro analysis is developed to show future signal timing at the proposed intersection during the AM peak period, PM peak period, weekend peak period, off-peak period and late-night peak period.
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