Signal Design and Plan Reading
Signal design questions test whether you can read a plan set the way its author intended. A typical set includes a title sheet with general notes and a legend, a plan view showing poles, signal heads, detectors, pull boxes, and conduit runs, a phasing and sequence diagram, a riser or cabinet wiring diagram, and schedules for conduit, cable, poles, and foundations.
Read in order: legend, plan view, phasing diagram, then schedules. The phasing diagram is the cross-check - every vehicle head on the plan must have a phase assignment, and every phase needs detection and a display. Left-turn displays, protected-only versus protected/permissive operation, and overlap assignments are the usual source of design errors, so verify them against the notes rather than assuming.
Dimensions to verify: overhead signal faces 15 to 19 ft above the pavement, pedestrian heads and pushbuttons at accessible heights and reach, conduit cover depth per the standard specification, and pull-box placement that keeps bends and runs pullable.
Traps: sheets marked NOT TO SCALE, revision clouds and delta triangles that change a dimension or note, addenda issued after bid, stationing running opposite the direction you assume, and the difference between a design drawing and an as-built.
Rule of thumb: pedestrian clearance time equals crossing distance divided by 3.5 ft/s walking speed, rounded up. A 60-ft crossing gives 17.1 s, so specify 18 s of flashing DON'T WALK, then add the WALK interval.