The Overloaded Refrigerated Run Down Shipka Pass
You drive a 12-tonne rigid refrigerated truck with a two-axle trailer, total laden mass 26.0 t against a design gross combination weight of 24.0 t. You left Plovdiv at 05:40 with a delivery slot in Gabrovo at 10:00. On the climb toward Shipka Pass the coolant temperature has risen from 84 °C to 101 °C and the warning lamp is on; the ambient temperature is 31 °C. Your tachograph shows 3 h 05 min of driving since your last 45-minute break, which you took at 03:00. The customer has already threatened a penalty clause of 400 BGN per hour of delay. Your dispatcher tells you to keep going and switch off the air conditioning to cool the engine. The road ahead descends for 9 km at an average 7 % gradient.
1. Evaluate the dispatcher's instruction to continue with the air conditioning off. What must you actually do, and why?
Read the worked answer
The instruction is not acceptable. An active coolant over-temperature warning at 101 °C on a 7 % climb is a developing mechanical failure, not a comfort issue. Switching off the air conditioning slightly reduces engine load but does nothing about the underlying cause (low coolant, failed thermostat, blocked radiator, fan fault) and it removes a driver-comfort factor on a 31 °C day.
Reasoning steps:
- Warning lamp plus a 17 °C rise above normal operating temperature means stop-and-inspect, not continue-and-monitor.
- The vehicle is also overloaded: 26.0 t against a 24.0 t design GCW. That extra 2 t is exactly what turns a marginal cooling system into an overheating one on a long climb, and it also affects braking on the 9 km descent.
- Continuing risks warping the cylinder head, losing coolant entirely, or a fire in the engine bay - costs far above 400 BGN/hour.
- The correct action: stop at the first safe place, let the engine cool, check coolant level and visible leaks, and call for technical assistance. Do not open a hot pressurised cooling system.
- Inform the dispatcher in writing that you are stopping for safety and that the load exceeds the permitted combination mass, so the delay is not attributable to you alone.
2. The vehicle is repaired and you resume. Analyse your driving-time position and what you may legally do to reach Gabrovo by 10:00.
Read the worked answer
At the moment of stopping you had 3 h 05 min of driving since the 03:00 break. The daily driving limit is 9 hours, extendable twice per week to 10 hours, so there is plenty of daily driving left. The binding constraint is the break rule: after 4 h 30 min of driving you must take an uninterrupted 45-minute break, which may be split into 15 minutes followed by 30 minutes.
So you have 1 h 25 min of driving before the break becomes compulsory. You cannot 'bank' the repair stop as a break unless you genuinely had no driving and no other work for the required period - a repair during which you were handling paperwork or supervising the mechanic is other work, not break.
Options:
- Drive up to 1 h 25 min, then take a full 45-minute break; if the remaining route fits inside that, you arrive legally.
- Take a 15-minute break now, then you may drive a further 1 h 30 min before the 30-minute part is due - useful if the repair already gave you a natural pause.
- Do not exceed the 4 h 30 min threshold to save the penalty clause. A 400 BGN/hour clause is a commercial risk; an infringement is a legal one and the driver carries it.
Also note: the 9 km descent must be taken in a low gear with engine braking, not on the service brakes alone, given the overload.