I like how each car feels very different because of the different colours, horns and speeds. The red car especially was pretty funny when I first saw it haha
The background car sounds are pretty good and I like how you change the pitch of the horns slightly so it doesn't feel too repetitive.
I don't really think you need a level system for this kind of game, I couldn't tell the difference in difficulty between some levels. It would probably be easier to have a high score system where you have to keep crossing roads that increase in difficulty and as you get further the harder vehicles show up.
Also, lane markings would be really helpful and it would make the player seem like they are always moving. Right now when the whole screen is just grey it feels like the player is standing still.