TECH ED’S CHOICE
SPEEDING TOUR SHUTTLE, OR FAULTY TRACKER?
Having been a shuttle driver in the tourism industry for well over 20 years, my motto has always been “safety first” and I am proud of my clean record.
The buses we use are 14-seater Toyota Quantums. These are speed controlled at 100 km/h, limited to a maximum of 110 km/h and are fitted with tracking devices recording time, speed and position.
Recently, to my surprise, I was informed I exceeded the speed limit of 100 km/h by quite a margin. It happened coming down to the toll gate at Huguenot Tunnel where it is quite steep. My driving style is to use engine braking in a lower gear to reduce wear on the brakes. Imagine my surprise when I was told I was speeding at 165 km/h, according to the tracking data. Can CAR’S experts explain if such a high speed is even possible given the fact that the engine power is cut at 110 km/h (limiter) and help me prove my innocence? GERHARD PRETORIUS Via email
The aerodynamic drag of the bus is significant if we look at the claimed top speeds in unrestricted versions. Depending if it is a diesel- or petrol-powered Quantum, the top speed (unrestricted) would be 135 or 155 km/h.
To achieve 165 km/h travelling downhill would require your restricted Quantum to travel “freely” from 110 to 165 km/h using only gravity, as the engine power is cut at the former. This is highly unlikely, even on a steep downhill.
The only logical explanation is erroneous data from the tracking system. To prove your innocence, we propose:
• Requesting the tracking data of the infringement and inspect the speed-over-distance graph. It should be smooth with no spikes because any jump is physically impossible and may point to a loss of satellite signal, for example.
• Involving the tracking company, as it
reflects badly on its product.
• Conducting a “free-wheel” test down the same hill while recording the vehicle speed with another Gps-based system and having a Gopro-type camera capture the instrument cluster and road ahead view to show the indicated speed.
• Downloading a tracking app on your phone to record every journey in the future for comparison purposes.