I had a play around with it and it was a bit of fun, although it definitely needs work. It's a really nice concept. In the custom stage the background suddenly turns black and it lags. It needs sound effects, a main menu and different car colours and weights would be nice. First of all though removing the black screen problem is a must. As I said nice concept, just needs to be polished and expanded upon. Good job.
The box does not always fire from the reticle and also sometimes the box goes through the wall. This game would benefit from a main menu and more block structures to destroy.
Nice game. It would be interesting if you could choose how they drove, aggressive or passive. Are thay good at driving or not. That would make it a very good game :)
There is a problem where if you type in the name of an other player you can play as them. So you could improve someone elses score and they might not like that. Maybe instead your name is the kongregate username and that would advoid people playing as another person.
 "AdVenture Capitalist"){kind=icon}
 "Idle God 3"){kind=icon}
 "Car Crash Simulator 2013"){kind=icon}
 "Spatial"){kind=icon}
 "Accelerator"){kind=icon}
 "War Aircraft Jigsaw"){kind=icon}
 "Mario Logic"){kind=icon}
 "Snakes On A Cartesian Plane"){kind=icon}
 "Cube Murder"){kind=icon}
 "You Are The Road - Molyjam 2012"){kind=icon}
 "Pixel Zen"){kind=tracking}
 "Super SOPA Bros."){kind=icon}
 "Gravitee 2"){kind=icon}
Nope, it's a remix! =)