The Interlock Will Not Release
At 4:45 p.m. a 40-foot transit bus is stopped at a downtown curb with 38 passengers aboard. The right rear door has just closed after a passenger with a stroller exited slowly. The brake-door interlock light stays on and the bus will not move. A passenger stands forward of the standee line to ask you a question. Another passenger presses the stop request even though the next stop is two blocks away. A driver behind you leans on the horn. On the radio, dispatch says: 'That interlock is a nuisance. Pull the fuse and get moving.' The street has a slight uphill grade, and the bus is in a no-standing zone. You have the parking brake set, the transmission in neutral, and the door-control switch within reach.
1. What is the purpose of the brake-door interlock, and why should you not pull the fuse as dispatch suggests?
Read the worked answer
- The interlock prevents the bus from moving while a passenger door is open or not fully latched. It protects passengers from being dragged, falling, or caught in a closing door.
- The light staying on means the system still senses an open door or a fault. Possible causes include the stroller keeping the door from fully closing, a misaligned door sensor, or a failed interlock circuit.
- Pulling the fuse disables a safety device. You could move with a door open or with a passenger still in the doorway, and you would be operating a defective bus contrary to policy.
- First re-check the door: clear the doorway, close it fully, listen for the latch, and cycle the door control. If the light remains on, keep the parking brake set and call maintenance. Dispatch should send a mechanic or a replacement bus, not instruct a bypass.
2. How do you manage the standee, the stop request, and the impatient driver while the bus is disabled?
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- Standee: Ask the passenger to move behind the standee line or take a seat. No one may stand forward of the line while the bus is moving. On an uphill grade, a standing passenger is at greater risk; follow your agency's standee policy. If the passenger refuses, do not move the bus.
- Stop request: Acknowledge it. Explain that the bus has an interlock fault and cannot proceed yet. If the next stop is two blocks away, passengers may choose to walk, but only let them off at a safe curb, not into traffic.
- Impatient driver: Do not respond by moving unsafely. Keep the parking brake set and use hazard lights if appropriate. The driver behind can wait; a collision or dragged passenger is worse than a delay.
- Keep passengers informed and ask dispatch for a mechanic or replacement bus.
3. If the interlock cannot be cleared and a passenger reports smoke near the rear door, what evacuation and equipment steps apply?
Read the worked answer
- Treat smoke as a fire until proven otherwise. Stop, set the parking brake, and shut off the engine if safe.
- Evacuate passengers away from the bus and upwind if there is fire. Use the nearest usable exit: front door, rear door if it opens, side windows, or roof hatch. Do not send passengers through smoke.
- Call 911 and dispatch. Use the fire extinguisher only on a small fire and only if you can do so without blocking your own exit.
- Account for all passengers at a safe assembly point; check the aisle, seats, and restroom.
- Do not re-enter. Afterward, tag the bus out of service, report the interlock and smoke, and complete an incident report. Replace or recharge the extinguisher if used.