Test Drive Unlimited Solar Crown

At the start of the game, roads will be in two case (in a minimap viewing) :
Dark Grey for asphalt roads
Dark Yellow for the cross country roads (off-road)

From Main map, however, it turn out asphalt roads are blue instead of grey...

After discovering, means after yoy have drive on the road on question, it turns to be more brighter road (dark blue to blue (aka dark grey for white) and dark yellow to yellow...

To be noted, there are a few hiddens roads with dotted line but to see them, here is a website with a map to see them : https://www.oghub.fr/fr/maps/tdusc (include all hidden wrecks and radiant prices).

After you reach 50% of road driving, acheivement is yours.

PS : you earn reputation after each 1% of road discovering but would be long to write the whole reward list, to be shorter enough, 1% = 100xp and more you drive, more it addition 100 xp per 1% discover.