Wow this definitely seems like one of those game jam games that becomes a popular steam game later down the line. It reminds me of "mini motorways" a lot. I love the ambition and I would say you pulled it off with flying colours.
Though a game made in 96h is always going to have some rough edges. If you plan on working on this more I have some feedback:
1) Changing between road types needs to be smoother. Building a bridge is a bit clunky since it requires 9 inputs:5 mouse drags and 3 button clicks (Drag road, space, Drag ramp, Space, Drag Bridge, Space, Drag Ramp, Space, Drag Road). There's a few ways to go about this, you could make it automatic, ditch the ramp type entirely and just allow roads and bridges to connect, or maybe "click+scroll" can just change the height of the road. Either way I think 9 inputs for 1 bridge is far too much.
2) Remove the "directional roads" mechanic. I'm not sure there's any reason the player would want to place the roads the wrong way around, so just make every road bidirectional. For example in the image below it's not immediately clear what is wrong and why the game says the loops are incomplete when they are clearly complete. What's worse is that finding the problem requires deleting every piece and putting it back to see if it's the one that's backwards. The graphics give no indication which way the roads are facing.
3) Lastly I would probably make the "erase" just erase tiles of all types. Since if I want to rethink a section it's a bit tedious to delete every type one at a time.
With all this negative feedback I don't want to give the impression that the game is bad, I actually think it's one of the best games in the jam.