Ten-Day Signal Shutdown at a School Route
A widening project requires relocating the existing span-wire signal at a four-leg intersection. The contractor proposes to turn off the signal for 10 working days, bag the signal heads, and use two flaggers on each approach from 7 a.m. to 5 p.m. only. At night, all lanes would remain open and the signal would stay dark; the contractor argues that traffic volumes drop after 6 p.m. The arterial is posted 45 mph with 28,000 ADT and a school crossing 300 feet from the intersection. The proposed temporary traffic control plan shows a 300-foot lane-closure taper for a 12-foot lane on the 45 mph approach, no buffer space, and a pedestrian detour that routes children through the adjacent shopping-center parking lot. The contractor has an approved project permit, but the temporary traffic control plan has not been signed by a professional engineer. Work is scheduled to begin in five days.
1. Is the proposed signal shutdown and flagging operation acceptable? Explain the factors that govern this decision.
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Not as proposed. Turning off a signal at a 45 mph, 28,000 ADT intersection creates an uncontrolled intersection for the hours when flaggers are not present. The nighttime volumes may be lower than the daytime peak, but they are unlikely to be zero, and drivers who are familiar with the signal will not expect it to be dark. Flaggers can be used to control traffic during construction, but the control must cover all hours the signal is out of service, and flagging at a high-volume intersection can create queues that extend into the 45 mph approach.
The school crossing 300 feet away is a major factor. Children may cross during the work, and the proposed pedestrian detour through a shopping-center parking lot exposes them to vehicle traffic, is not an accessible route, and is not a controlled crossing. The decision should consider whether the existing signal can remain in operation during staged construction, whether a temporary signal is needed, and whether the work can be done at night with full lane closures and a proper temporary signal or uniformed officers. The TTC plan must be prepared and signed by a qualified professional engineer and accepted by the agency before work begins.
2. Identify the temporary traffic control deficiencies in the setup and state the corrections you would require, including the taper length.
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The plan has several deficiencies:
- Taper length. For a lane closure on a road with a posted speed of 45 mph, use the formula L = W × S, where W is the lane width and S is the speed. Here L = 12 ft × 45 mph = 540 feet. The proposed 300-foot taper is too short.
- Buffer space. The plan shows no buffer space between the taper and the work area. A buffer space is required to separate traffic from workers and equipment; the length must follow the standard table for 45 mph.
- Signal shutdown without full-time control. The signal cannot be left dark at night with all lanes open unless the intersection is controlled by another acceptable method. Either maintain the signal, use a temporary signal, or provide flagger/officer control for all hours of shutdown.
- Pedestrian access. The detour through the parking lot is not an accessible pedestrian route and lacks protection from traffic. Provide a signed, barricaded pedestrian path that meets accessibility requirements, or provide a controlled crossing with appropriate supervision and warning devices near the school.
- Plan approval. The TTC plan has not been signed by a professional engineer. It must be sealed and accepted before mobilization.
Require a revised plan showing the 540-foot taper, buffer space, pedestrian route, and the signal-control strategy for daytime and nighttime.
3. What coordination, notification, and documentation steps must be completed before work begins?
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Before mobilization, complete and document the following:
- Agency approval of the revised TTC plan signed by a professional engineer, including the signal-shutdown and temporary-signal strategy.
- School coordination: notify the school district and the crossing guard program, confirm school hours and arrival/dismissal times, and arrange for adult supervision or police support at the crossing if the route changes.
- Emergency responder notification: provide the police, fire, and EMS with the closure dates, lane restrictions, and temporary signal operation.
- Public notification: post advance warning signs and issue a public notice through the agency and school, including the dates and the pedestrian route.
- Utility and railroad coordination if the signal relocation affects service or preemption, and confirmation that the temporary signal has power and detection.
- Pre-construction inspection and records: photograph existing conditions, confirm the contractor's traffic control devices are on site, and file the approved plan, permits, notifications, and contact list.
At the end of each shift, document the traffic control in place, any incidents, and the signal status. Final records should include the as-built changes and the date the permanent signal was restored.