Wednesday, May 22, 2013

Speedo Musings

For 230,000km I have been staring (well - glancing) at this speedo on my cheapo Japanese car.
I find it very clear & easy to use.
The only negative is that it marks 20-40-60 etc whereas nearly all speed limits are 30-50-70-90-110-130.

Our latest, very expensive German car doesn't do nearly as well.

The speedo is not directly in front of the driver, so suffers parallax errors.
The numbers aren't so obviously aligned with their marks.
Worst - the scale suddenly changes, between 40 & 60 (presumably at 40?) so interpolation between numbers requires careful scrutiny & mental gymnastics!
Checking speed requires concentration & takes your eyes off the road for over a second.
Somebody should get the boot for this...

Directly in front of the driver is a screen with all sorts of useful but incidental stuff, like time & temperature, which would be better in the dash where everybody could see it.
That screen can also display driver-interest items like fuel consumption & range.
Or, it can display speed, digitally.
I found that surprising - until I tried it.
Then I found that checking my speed took the merest fraction of a second, without even needing to refocus or look directly at the number.
Now, I often have it set to digital speed and compare the 2 methods.
The difference in time & ease is so flagrant that there is absolutely no contest.
On safety grounds, legislation should encourage or impose (ouch! - see below) digital readouts.

Of course, the readout should be bigger & nearer the line of sight.
Then it would not be necessary to look away from the road at all.

Another novelty with the new car (late adopter...) is a GPS.

Apart from its obvious function of navigation, the GPS provides 2 arguably-more-useful functions:
1. It indicates actual speed with (presumably) better accuracy than the vehicle speedo.
Certainly the difference is around 8%.
2. It indicates local speed limits, and does it very well.
Obviously it can't handle temporary limits & obviously it depends how frequently you update the data, but it seems to offer better reliability that any, even careful, human driver.

Which leads me to the conclusion that what I want, and what everybody needs, is a good, big, head-up display of GPS-accurate speed & of up-to-date local speed limit.
With a warning light...

That has to be achievable today & would save a lot of people a lot of time, money & maybe injury.

I am aware of alternative systems which actually read speed limit signs, but have my doubts about their reliabilty in real traffic conditions.

Parting thot: "What is ominous is the ease with which some people go from saying that they don't like something to saying that the government should forbid it. When you go down that road, don't expect freedom to survive very long." - Thomas Sowell

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