Rather odd routes ...

[LongQ]

I guess we all know and accept that most of the mapping systems out there - or rather their databases - have a few oddities that take us on unusual routes. If I use mine from home most commonly it will take me to the north of the village to start with, which is fine except that the road it selects is a one lane country track mainly used for the last 30 years to my knowledge for walking dogs and riding horses. I did tell the vendor - the last update didn't change anything.

Anyhow, this weekend I leant my unit to someone for a trip to Cardiff. Easy journey but they had never been before. So I 'programmed' it for them. My route would be a couple of miles to the A42, then M42 all the way to the M5, south to the M50, then the A449/A40 to J24 of the M4, along the M4 to the M48 and into Cardiff. Used the route many times a few years ago. Much more scenic than the M5 to Bristol route and avoids paying to get into Wales. Distance is probable about the same. Likewise time - little or nothing in it.

So the first route plan it came up with, using the 'fastest' option, followed my route to the M5 and stuck with it down to Bristol, then picked up the M4 to Cardiff. It failed to warn me about the bridge Toll I subsequently realised.

Hey, no problem, the calc probably has the motorway route as a minute or so quicker than the A roads - so I went for a recalc to get an alternative route. Yep. Got the M50 route this time , but hang on. Now it is taking me down the M1 to the M69 then the M6 before joining the M42. Why do that?

Try another re-plan.

"Do you want to avoid a Toll?" Ah! It's recognised the bridge this time .... er, no. Another totally different route that heads West and picks up the M6 Toll road ...

Try again ...

Ah, journey time now up from about 3 hours to nearer 5 and a half on a route that takes in a lot of North Wales and, just possibly, most of the decent rally stages the old Lombard RAC used to follow.

So, anticipating that the next plan might take me via Edinburgh and Cherbourg, I went back to the first route and then used an 'Avoid here' - basically Bristol which imo is always a good place to avoid - and it seemed happy with that. Journey time and distance almost exactly the same as the M5/M4 and bridge route it preferred.

Maybe that is the problem.

If the secondary selection, though 35% different in the route roads selected, seems too similar to the first in terms of distance and time (and 65% of the roads of course) maybe it discounts the second most obvious route.

Very odd. Ayone else have any similar examples?

Needles to asay the system borrower totally forgot what I had told him and ended up going over the bridge, paying the toll and arriving at the second location he was aiming for rather than the first as I had left the second one in place when he took the system away on Friday night. Just goes to show that these things won't work too effectively on a hand out basis for poeple who are not really familiar with them. Still, at least it got them on the right motorways ... why oh why did the schools stop teaching proper Geography?