The majority of local & rural roads have no set speeds. You can view them while you drive, by setting an option in your Status Bar. It's called something like, "Show Max Speed Next to Your Speed."
If your current road (usually a Highway) has one, it'll appear as a fraction: "45/55" __where "45" is your speed & "55" is the road's limit. And an improper fraction, "62/55" means you're speeding & trips the TomTom's speed alert warning, usually at +3 mph (+5 kph) over the limit. If you really exceed the limit, say +7 mph or more, the warnings stop. Presumably, because you're passing another car & not itching for a Huge Fine.
However, for most roads, you'll have to go in & manually set their speeds, which is a wholly tedious process. You make the actual changes in the Map Corrections area. I've done this for a lot of roads in and around my area, but every time a map upgrade comes out, this data is lost.
Somewhere in these forums, I posted a guide to adding road speeds. Here's my Number One Tip for adding them:
use a stylus!
Good Luck!
R?