Get to full speed (preferably but not necessary) and press 
'N' for neutral. Now you can cruise along at full speed with 
easy steering and invulnerability.  As long as you stay in 
neutral you will have unlimited time as well. 
 
Another trick is to repeatedly hit the 4 key (4th gear) until 
the program has an error.  Continue with the right mouse button.  
Repeat until you get a high score.