surfaces.ini tells the game how much grip a surface has. instead of using ROAD GRASS KERB SAND which are programmed to work automaticly regards game engine logics. you can name them yourself. and that's where they go. the surfaces.ini file. one does this to have multiple different grip values on multiple different pieces of track.
the single digit concept whilst related is something different. for example. 1WALL01 is a wall, but you cant drive on it unless there is surface entry for WALL, either a surface is .
1 collidable. or (no digit) not collidable. and whilst its collidable it can be drivable or not. so that's why you have the digit and the name together for an explicit drivable road surface object. --- but clear the digit concept out of your head now, its not related. its not related and just the question number 1 that the game asks, everything after this is a separate piece of game logic.
to clarify, an object can be Visual only, or Collidable. or Collidable and driveable.
visual = named object where name doesn't appear in surfaces.ini and not prefixed with 1-9
collidable = object name prefixed with any digit 1-9
collidable and drivable = prefixed digit and title with that title defined in surfaces.ini
the 1 digit not appearing in the surfaces ini is confusing you because you relate them together, but they not related. they just used together, so no need to make digits in the surfaces ini. just capital letter title of roads with "differing" grip values.
if a ROAD001 is not collidable , its not drivable. that's why it needs to be 1ROAD001. so its two stage process. 1 game engine looks to see if its collidable. 2 it then asks ,is it a drivable surface. it then looks for the name of the object and matches it so what is in the surface.ini file. fi there is no match, it still wont work. all must matchup.
btw, don't worry about the clock running, you need make a route for the AI to drive the track still

and that requires a lot of learning. think about all this in terms of logic and what the game engine requires.