You *accelerate* on the top part of the screen, you only lose speed when you hit something. So you have to spend a bit of time in the upper part to gain speed and then move around more freely to dodge better.
A warning sign and honk happening before cars appear on screen was planned, but I didn't manage to implement it in time for submission. I did get to it yesterday though and it will be included with a general polish update that releases once voting has finished.