I downloaded the game and beat the normal and hard highscore in about 10 minutes
Fun game, I enjoyed it very much.
Here some improvments I would suggest:
1. Change up the music a bit. It gets pretty annoying hearing the same 10 second riff over and over and over.
2. When you enter a tunnel you should be exit the other tunnel from the same position you came in through, because I could abuse this a bit by coming in to the tunnel from weird angles and exiting safe
3. There's a bug (or feature?) that when you exit a tunnel you are invincible for a second. Which means that I can run over any cars when I exit a tunnel without damaging my own or even losing points. Although I think you should in some way be able to at least react when you exit a tunnel, otherwise tunnels would be a deathtrap.
4. The car auto-adjust itself to stick to the road, but the annoying part is that sometime it does and sometimes it doesn't. And this can get really annoying when I one time tap a direction and the car moves a bit to that direction and then auto-adjust while other times I tap in a direction and the car doesn't auto-adjust and I go offroad. Be more clear when the car will auto-adjust or have the car do it all the time or no time at all.
5. A master slider for audio would be nice, so that I won't have to minimize the game and do it through windows.
6. Gamepad support (this can obviously be added further down the line, but it would be nice to have)
7. Being able to press enter or space to quick restart a level after failing it. Because you have your hands on the arrow keys or wasd.
8. Being able to rebind keys (for obvious reasons).