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Knowing your limits

In your reply you suggest to HR of Oakham that he needs a satellite navigation unit that shows the prevailing limit and the true speed. I have two problems with this. Constantly watching the display for your speed and the limit could distract you from the road. Even the latest updated database used by TomTom, does not know the speed limit on all roads. In South Gloucestershire, for example, there are many minor roads where it does not have the speed limit recorded, so will not display it. And, even on the A38, TomTom is not aware of all the latest applicable speed limits (some of which have been in force for some time). So total reliance on a SatNav system for avoiding speeding would be dangerous.

Asked on 13 February 2010 by A.C., Bristol

Answered by Honest John
Put the TomTom in your line of sight and it does not distract your eyes from the road anything like as much as looking away from the road to a speedometer. But you have exposed a major flaw in the thinking behind the proposed Intelligent Speed Adaptation that controls cars speeds by GPS. If TomTom does not know the prevailing limit, then how will ISA? And, of course, if a 70mph road crosses a 30mph road, how will ISA cope with that?
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