Tom tom route options

[TomDavison]

I've had a play with the routeing options on my 700 over the last couple of days.

First attempt was using shortest route, and that was soon scrapped as it took me off every by-pass, and through the villages.

I then tried avoid motorways, and that took me on a scenic route, mostly on A roads, and always around the by-passes. A 1hr 40 journey using motorways, was estimated as a 2hr 15 journey, but I made up over 15 mins because I was driving (at 50mph on 60mph roads) faster than the 700 expected. What was interesting is that it took me through 2 rail bridges with height limits, and no way to turn around. One was 11ft, 6ins. Glad I wasn't driving a lorry.

On the motorway, however, with speed set at 70mph on the satnav, I couldn't keep up with the 700 expectation, and over 30 miles lost a couple of minutes. It looks like the planning speed for motorways is about 74mph. (could be 120kph)

Bottom line is you are likely to arrive earlier than originally estimated if your journey does not include motorways, but later than estimated if it does, especially if the traffic stops you cruising right on the limit.

[Andy_P]

Swings and roundabouts. I usually find over a long journey involving a motorway stretch in the middle, it's remarkably close.

Where it really falls down is when I'm "5 minutes" away from work in the rush hour and I'm going to be 1/2 hour late!

[CavesOfTQLT]

[Oldboy]

[TomDavison]

[Mullet]

Consider also the inacuracy of your speedo, typically upto 10% understated.

[Mullet]

[Oldboy]

[mmman]

I find it almost spooky how close the original estimated time of journey, immediately after you input a route, is to the final result. Doesn't seem to matter if you're stuck in a half hour jam or sail straight through 8)

As for the speed display on the satnav, I like to use this to cruise past a Traffic car at a speedo reading of 80, knowing that it's actually more like 71/72 I guess the other drivers keeping up with me are either hoping that I'm the one to get pulled, or have TTs as well...

Incidentally, not all speedos are actually 10% over: Toyotas are a good 10%, Hondas are almost spot-on accurate, while Mercs are somewhere between. None is under the true speed.

[TomDavison]

[TomDavison]

[theripper]

I've always been under the impression that the ETA function was dynamic, if you slow down the time increases and if you speed up it decreases and when you are 1 minute away from work it should be almost exact. :D

[ColinS]

I believe it uses fixed MPH as previously stated but will recalculate based on the distance remaining to your destination. It therefore will be more acurate the closer you get.

[TomDavison]

There seems to be a little confusion here, so hopefully, I can explain better.

Lets say that you plan a 60 mile journey, and tomtom assumes you are going to drive at 60mph. You set out at midday, so your arrival time is listed as 1pm. If you actually drive at 70mph, after half an hour, you will have covered 35 miles. Tom Tom still assumes you will drive the rest of the way at 60mph, so by now your arrival time should be 12.55. (25 miles remaining at 60mph)

If you had driven at 50mph, you would by now have covered 25 miles. Tom tom will assume you drive the remaining 35 miles at 60mph, so your arrival time will indicate 13.05

After 59 miles of your journey, at 70, it will now be 12.51 and you will get an arrival time of 12.52 (one mile to go at 60mph). If you had driven 59 miles at 50 mph, the time would now be 13.11, and your tomtom would show an arrival time of 13.12 (one mile to go at 60mph)

So the arrival time is refined throughout the journey, and gets more accurate the closer you are to your destination.

What we don't know, are the speeds that tomtom is using to calculate your eta. However, if you drive at a steady speed, and your eta doesn't change, you must be driving at the speed that the TT expects. If your arrival time gets earlier, you are driving faster than TT is planning, and if your time gets later, you are driving slower.

What I had pointed out is that with my speed at 70mph on the satnav, over a 30 mile distance, my ETA was extended by 2 minutes. So I was driving about 4mph slower than the TT had expected. This indicates that the TT assumes that on motorways I would be driving at about 74mph.

[Texy]

Good explaination Tom, and this is the crucial point, as it doesn't involve anyone getting calculators out whilst driving :

[quote="TomDavison"]if you drive at a steady speed, and your eta doesn't change, you must be driving at the speed that the TT expects.quote]

Texy

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