Civil Engineering > GATE 2026 SET-1 > Traffic Engineering
Traffic is moving on a 6-lane dual carriageway road. Traffic volume per direction during peak hour (08:00 am to 09:00 am) is 6000 veh/h. It is assumed that the traffic is distributed uniformly across the lanes in each direction. Just at 08:00 am, a truck goes out of order on the middle lane of one side, thus disrupting the traffic on that lane in one direction. The lane capacity under normal conditions is 2000 veh/h/ln and under queue formation it is 1600 veh/h/ln. The traffic resumes at 08:30 am on removing the truck from the middle lane. Hourly traffic volume after 09:00 am reduces to 5000 veh/h/dir.

The number of vehicles in the queue at 10:00 am is ______ (in integer).

Correct : 0

Traffic volume per lane = 6000/3 = 2000 veh/h/lane, which exactly equals the normal lane capacity.
08:00 to 08:30 — Queue formation:
The disrupted middle lane can only serve 1600 veh/h while 2000 veh/h arrive. Queue grows at 2000 − 1600 = 400 veh/h. Over 30 minutes: queue = 400 × 0.5 = 200 vehicles by 08:30.
08:30 to 09:00 — No dissipation:
Lane restored to 2000 veh/h capacity. Arrival rate is still 2000 veh/h (same as capacity). Queue dissipation rate = 0. Queue stays at 200 vehicles at 09:00.
After 09:00 — Queue dissipation:
Volume drops to 5000 veh/h/dir = 5000/3 = 1667 veh/h/lane. Lane capacity = 2000 veh/h/lane. Excess capacity = 2000 − 1667 = 333 veh/h. Time to clear 200 vehicles = 200/333 h = 0.6 h = 36 minutes. Queue clears at 09:36 am.
At 10:00 am the queue has already cleared. Queue = 0 vehicles ✓
Correct answer: 0 ✓

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traffic queue formation dissipation GATE 2026 GATE Civil 2026 Set-1 Q59 lane capacity queue traffic engineering GATE vehicles in queue 10am zero GATE civil traffic incident queue 6-lane road GATE queue dissipation lane restored volume drop GATE

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