Night Lane Closure Through an Active Signalized Intersection
A paving subcontractor wants to close the right through lane of a two-lane, 12-ft, 40-mph arterial from 7 pm to 5 am for milling and overlay. The work is 350 ft downstream of a freeway off-ramp. The intersection at the closure is fully signalized with marked crosswalks on all four legs, serving an apartment complex and a bus shelter. Counts during the closure window show 850 vph on the arterial and 60 pedestrians per hour around 9 pm. The subcontractor proposes to (a) set the signal to flashing yellow for the arterial and flashing red for the cross street and have flaggers wave traffic through, (b) close the crosswalk on the affected leg, and (c) start the first cone 150 ft ahead of the taper to keep the closure short. The agency inspector must respond tonight.
1. Evaluate the flashing-signal-plus-flagger proposal. Is it acceptable, and what would you require instead?
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Reject it as submitted.
- Mixing a flashing signal with flaggers creates an unresolvable conflict of authority. A driver approaching a flashing yellow has been told to proceed with caution; a flagger waving them forward says the same thing twice, while a flagger holding them says something the signal contradicts. When the two disagree, some drivers obey the signal and some obey the person.
- Flashing red for the cross street on a 40-mph arterial with 850 vph is a stop condition the minor street did not have before. That is a real operational change with a real crash cost, imposed to save the contractor a maintenance-of-traffic plan.
- Flaggers waving through a live intersection also create a pedestrian conflict. With 60 pedestrians per hour crossing at 9 pm, a flagger focused on vehicles will not reliably see someone stepping off the curb in the dark.
Require instead:
- If the closure does not remove a through lane at the stop bar and does not affect lane assignment, keep the signal in normal stop-and-go operation. That is the lowest-risk configuration and needs no flash decision.
- If the closure does remove a lane at the stop bar or requires alternating traffic, the signal must be taken fully out of service - heads turned, bagged, or covered, with the agency notified, appropriate temporary signs and flaggers, and clear removal of any conflicting lane-use indications.
- Provide lighting for the work area and the temporary traffic pattern, and verify the signal heads remain visible against the construction lighting.
Document the decision, because the question of who authorized the flash will be asked later.
2. Compute the merging taper length for the 12-ft closure at 40 mph and describe the buffer, advance-warning, and ramp-interaction elements you would require.
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Taper length first.
For a merging taper at 40 mph, L = W × S, where W is the offset in feet and S is the speed in mph:
L = 12 × 40 = 480 ft
The 150-ft cone spacing the subcontractor proposed is a third of the requirement and is rejected on the arithmetic alone.
Buffer and advance warning:
- Provide a longitudinal buffer between the taper and the work area. Typical guidance scales with speed; at 40 mph a buffer of several hundred feet is expected. Do not let the buffer be consumed by equipment staging.
- Advance warning signs must use the distances from the MUTCD Part 6 tables for a 40-mph condition (verify the current edition's table). Add the sign sequence in the correct order and ensure signs are not shadowed by the ramp gore or by parked equipment.
Ramp interaction - the constraint that governs the design:
The closure is only 350 ft from the off-ramp, but the merging taper alone is 480 ft plus advance warning. Laid out as proposed, the taper would begin inside the ramp merge area, putting ramp traffic into the taper and the closure. Options:
- Relocate the taper downstream of the merge, so the ramp traffic merges before the closure begins.
- Close the ramp lane or the ramp itself for the same hours, with its own advance warning and detour.
- Restrict the work to hours when the ramp volume is negligible and provide a flagger at the merge.
Any of these needs a revised plan signed by the traffic control supervisor and accepted before the first cone moves.
3. Is closing the crosswalk on the affected leg acceptable? State the conditions you would impose.
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Only with a safe, accessible alternate route - otherwise no.
- At 60 pedestrians per hour, this is not a low-volume crossing that can simply be deleted. Closing one leg without providing a marked alternative pushes people into the live lane or into an unmarked midblock crossing in the dark. That is a foreseeable crash and it will be traced to the traffic control plan.
- ADA: a pedestrian route must remain accessible. If the crosswalk is closed, the detour must be marked, firm and stable, free of vertical discontinuities over the agency threshold, and it must not route pedestrians behind equipment or into a lane open to traffic. Provide detectable warnings at the temporary crossing point and keep the existing curb ramps serviceable or provide temporary ramps.
- Signal implications: if a crosswalk leg is closed, the associated pedestrian signal must be deactivated or bagged so it does not invite pedestrians into a closed area, and the controller's pedestrian timing for that phase must be adjusted. Do not leave a pushbutton live on a closed crossing.
- Lighting: the temporary pedestrian route must be lit. This work is at night.
Conditions I would impose in writing: a marked temporary pedestrian route on the same side of the arterial or across the adjacent legs, maintained for the full closure window; temporary detectable warnings and signage; illumination of the route; bagged pedestrian heads on the closed leg; and a nightly check that the route is still passable before the closure begins.