True speedo?

AUSTRALIAN Design Rule (ADR) 18/03 - not many would have heard of it and even less taken time to have read it. It's the standard to which the speedometer of every complying vehicle in Australia is adjusted. ADR 18/03 is also a major contributor to some of the conflict and misunderstanding that occurs between heavy vehicle drivers and other road users today.

Many believe that the speedometer of a vehicle is allowed to indicate a plus or minus tolerance of a vehicle's true speed. This is a misconception. Every new vehicle sold through the requirement of ADR 18/03 must indicate a speed faster than the actual speed of the vehicle. Testing units are allowed to have a tolerance of +/- 5% but not the speedometers. They must be set to a speed below that indicated by the testing unit. In the case of cars and heavy vehicles they must be set to 6kmh below the indicated speed of the testing unit.

Because they have the ability to be adjusted, most heavy vehicle speedometers will soon find themselves being calibrated to indicate true speed not long after being registered. Light vehicle speedometers are not usually built with any ability to have changes made and this is where problems start, with a speed differentiation occurring between vehicles that leads to tailgating, intimidation, misconceptions and other issues.

With GPS units having alerted the public to the inaccuracy of their vehicle's speedometer this has gone some way to debunking the long-held myth of all trucks speeding at 110kmh when, in fact, they are obeying the speed limit, travelling at a true 100kmh. Not all drivers have a GPS unit and not all trust their accuracy, resulting in essentially two 100kmh speed limits existing - the true and the indicated.

While tailgating and other intimidating tactics are not to be condoned, they are a symptom of a problem that exists because of this discrepancy, partly brought on by the requirements of ADR 18/03. Quite often you will see vehicles at the indicated speed limit followed by heavy vehicles at the true speed limit wanting to pass, creating frustration and conflict between drivers. A good example of this was the short-lived reduction of the speed limit to 100kmh for all vehicles on the Newell Hwy in NSW. After input from many different parties the RMS has re-implemented the 110kmh speed limit on many sections, creating a positive or nil speed differential between cars and heavy vehicles and in theory reducing the number of vehicles that a truck travelling at 100kmh may need to overtake.

So what is the answer? Does the Australian Government take the initiative and change the requirement of ADR 18/03 so vehicle speedometers read true and accurate rather than the fib that they are mandated to, or should state governments, possibly through COAG, give consideration to increasing the speed limit for many suitable sections of highway to 110kmh or greater for light vehicles, mirroring in some way the situation of the '70s and '80s where, on the open road, there was a 20kmh differential when trucks were limited to 80kmh.

With improvements in vehicle designs and safety standards, as well as improved road quality some western countries are instigating 130kmh highway speed limits for cars and bikes with no negative effect on the road toll, so a uniform increase to 110kmh or greater for cars and bikes on suitable safe roads may be considered. The problem here is many government agencies have painted themselves into a corner with their misleading "Every K over is a killer" campaigns. Maybe VicRoads should consider this with the Princess Hwy between Laverton and Geelong. The only way a car can pass two trucks travelling in the left two lanes doing a true 100kmh is to effectively break the law and speed in the right lane.

If we can again get cars to travel as fast or faster than trucks, we may be able eliminate a lot of conflict on the roads.

Big Rigs

Topics:  chris blanchard in the know

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