Chrome 42+ disables NPAPI plugins like Unity3d plugin.
Copy and paste the following text into your browser: chrome://flags/#enable-npapi and enable the NPAPI plugin.
Or try another browser like Firefox
Choose one of the cool cars that you want to race on the highway. Then choose from various game modes and levels. Avoid all traffic very close to score points. Race with the WASD keys to Highway Racer 3D.