My 4 year old Garmin StreetPilot has the ability to tell it I'm driving various kinds of vehicle, from memory it has:
Pedestrian: presumably one way streets dont apply, can cross fields, cant use motorways
Car: (default)
Bus: I would be very worried if this function was ever used.
Truck: Avoids crappy little roads
Taxi: Can use bus lanes and presumably one way streets dont apply
Admittedly that thing cost 4 times as much as what TomToms cost now, but that's not really unusual for technology over 4 years.
How about we just encourage drivers of large vehicles to buy a more appropriate satnav?
Having seen the quality of some of the systems out these days, I'm starting to understand the anti-satnav argument. I had a recovery truck with a VDO Dayton system come to pick my car up from Liverpool about a year ago and take it to derbyshire. His satnav took him the wrong way out of my road, into a cul-de-sac, told him to do a U turn, turn left then do a right turn at a no right turn T junction (where the correct direction was actually left anyway). Fearing for my car, I got my Garmin out, pointed out that I have the correct destination marked already and that his postcode routing wont find it as it's in the middle of a field and let the driver use that instead.
His satnav wanted to take the cat and fiddle. I put mine into truck mode and it took us via M62->M1
So yeah, buy a Garmin, not a Tomtom if you drive a truck, please!