thats not a bad idea, but a tad unfunny because its still plain old tetris. and thats has been done to death...

but if you add some more features, this works. for example, you have a set number of stones. you not only have to build bridges, but also walls that keep the racers from going over a cliff for example. and once all racers, or the racer you bet on, passed the wall, you can crush it to use the blocks for the bridge.
in that instance, this gets competive, because the otehr players try to ruin your bridge and walls to build their own. each player has his set of stones but when you manage to deytroy another players car by crushing the bridge or wall you build, the player whose car died loses some stones and the player who killed it wins some stones.
THAT would be an awesome game. at least id like that...