Okay so the X button on the top right, I didn't realise would take me back to the main menu. If you try to play again after pressing the X no cars spawn. Also I think it was quite close to the X for closing the upgrade shop so I accidentally clicked it :(
Other than that, I liked the idea especially with the upgrade system, and being able to change the traffic lights. The music and sound effects were good as well and matched the theme!