TomTom One: change average speeds

Hi

I usually use "fastest routes" as planning preference with my TT One.
But I've observed that it often suggests motorways even if this route
is 40% longer than the shortest route. Often the route avoiding the
motorways takes me only a couple of minutes longer.

I think the software calculates the time that a certain route will
take with some average speed values depending on the different road
types. I would like to decrease the average motorway speed to my real
motorway average speed (which is seldom more than 120 km/h).

Is it possible to change these average values in some file on the TT?
I've searched the files on the TT with grep and googled for this
issue, but with no sucess.

Or is my assumption completely wrong? Thanks for any hints!


Martin