prediction shouldn't be this difficult

I have previously noted the inaccuracy of some computer predictions.  Tonight I observed how it also applies to cars.

As I started my trip, the GPS said the journey would take 2 hours 20 minutes, and the car instrument panel claimed I had 205 miles until an empty tank.

50 miles, and one hour, later, the GPS said the remaining journey would take 2 hours 5 minutes; more bizarrely still, the car instrument panel claimed I now had 215 miles until an empty tank.

So, it seems that the car thought I had taken 15 minutes to travel 10 miles backwards?

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goldfish brain

For the last eleven years and more, I’ve been driving between home near Cambridge, and work in York, nearly every week. I know the 350 mile round trip rather well by now. Despite this, I’ve taken to having the SatNav on during the journey. That’s because there can often be delays due to accidents, or road closures due to roadworks, and a little advance warning can let me choose a route more useful than the suggested diversion.

Last week, the inevitable happened. I was tootling up the A1 to York, when the SatNav advised me: “Road closed at J36 due to roadworks. Calculate alternative route?” Yes.

Whirr, whirr, whirr. “Confirm new route?” The map is very small, but I could see this new route at least approximated the M18 diversion I had already intended to take. So, yes, let’s take that one.

Pause. “Road closed at <somewhere I’d never heard of> due to roadworks. Calculate alternative route?” Okay, that’s a nuisance, so yes, calculate new route.

Whirr, whirr, whirr. “Confirm new route?” The map is very small, but I could see this new route looked close to the original A1 route.  But, hey.  Yes, confirm new route.

Pause. “Road closed at J36 due to roadworks. Calculate alternative route?”  Aargh! it had put me back on the original closed route.  I could guess what would happen next, but I tried it anyhow.  Yes, calculate alternative route.

Whirr, whirr, whirr. “Confirm new route?” Back on the M18 diversion. Yes, confirm. Pause. “Road closed at <somewhere I’d never heard of until a few minutes ago> due to roadworks. Calculate alternative route?”

Clearly the system has a diversion buffer of size one.  I decided to take the M18 diversion. Once I was on that bit of road, the system the quite happily found me a diversion around the diversion.

(left) intended route, but the A1 was closed around Doncaster; (mid) SatNav suggested alternative, but then found to be closed somewhere south of Selby; (right) final SatNav suggested route, once commited to the M18 east of Doncaster

very #FirstWorldProblems

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foggy thinking

Driving in fog this morning I was again bemused by something I notice every time when driving in fog.

Visibility was varying between 100-200 yards.  Nearly all the cars had their headlights on; about half also had their fog lights on.

A few had no lights on at all.  I assume these drivers are the ones who either think lights are for wimps, or who don't think at all.

But what bemuses me, every time, is the ones who have only their side-lights on.  In fog, you can see a car before you see its sidelights.  These drivers must have got as far as thinking "fog; put lights on" but not got as far as thinking "put headlights on because sidelights are invisible in fog, as I can clearly tell from all those other cars with only their sidelights on..."

I excuse those with sidelights comprising a little row of LEDs; I suspect these are visible from low earth orbit.

It's not just me.  Highway Code rule 226 says:

You MUST use headlights when visibility is seriously reduced, generally when you cannot see for more than 100 metres (328 feet). You may also use front or rear fog lights but you MUST switch them off when visibility improves 

(Although I MUST say, translating the round number 100m to 328ft is ridiculously precise.)

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