Routing Algorithm?

[MikeDJ]

Hi,

I have just had some intimate dealings with the TTG routing algorithm. Basically, there are temporary (?) roadworks on my daily commute to/from work which are causing horrendous delays, so I turned to TTG for alternatives.

First I put in home (start) and work (destination) and got planned route (my usual route, now with roadworks). Then tried Alternative 3 times, each of which produced yet longer and slower routes. Then I tried Itinerary, and set waypoints to take me down some small roads (Class 3, 2 way), which TTG had completely avoided in the 'Aternative' routes. The results were:

Normal Route: 13.6M 0:33 hrs
Alternative 1: 15.5M 0:42 hrs
Alternative 2: 18.0M 0:51 hrs
Alternative 3: 21.2M 0:56 hrs
Intinerary (back roads): 14.9M 0:42

In all cases, the planning option 'fastest' was used.

So my question - given that TTG tries to find 'fastest' alternatives, why did it not utilise the back roads at all (which produced the second fastest result) until I forced it to do so ?

BTW - TTG500, V5.201, GB_Plus-Map v571

Any ideas ?

[nej]

I think it's based on the classifications of the roads. A-Road and Motorways are faster (in theory 8O ) than little back-roads.

[wez99]

If you really want to use the back roads, try the shortest route option, but beware you may have to swap your car for a mule.

John
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TomTomGo730

[sgould]

I think the point is - why did the Go not offer the route put into the itinerary, since it is shown to take less time than the other alternatives that GO chose.

It does this to me too. And it's repeatable. I frequently go from Watford to Leamington Spa. The GO always sends me up the M40 and back down the M1. When I'm in Leamington and heading home, I choose "find alternative" and it offers me the same route as I went on the outward journey (M40), and saves 5 minutes
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iPhone 5 (hers!)
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[sgould]

I've just realised why the GO gets it wrong. If you choose "find alternative" it will avoid ALL the roads that it chose in the original route. The next "find alternative" will then avoid all the roads used in the previous two routes etc.

It may use the odd road again at each end of the route where there is absolutely no alternative.
_________________
TTGO 700 (dead)
iPhone 3GS + TT holder
iPhone 5 (hers!)
Western Europe Map
Eastern Europe Map
Kenwood DNX-4210DAB with Garmin maps

[rkm_hm]

[MikeDJ]

Hmmm - interesting. I see now why 'Find Alternative' produces increasingly bizarre and extensive detours (by ignoring all roads previously chosen).

I tried the 'Shortest Route' option on my example commute, and sure enough for the first time it chose some of the small roads instead of what I assume is the hierarchy of searching when in 'Fastest' mode of:
1. Motorways
2. A Class Dual Carriageways
3. A Class 2-way
4. B Class

I have yet to see a route planned first time using 'Fastest' which uses anything other than the above. Do you suppose it ignores all other roads in this mode , or have I just not found an example yet which truly would be fastest using smaller roads? (I live in Basingstoke).

Maybe in a predominantly rural area with a lower density of major road alternatives TTG would show a different behaviour ?

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