Wave def'n: A disturbance traveling through a medium by which energy is transferred from one particle of the medium to another without causing any permanent displacement of the medium itself.
Just to be anal
it's not a wave, because the cars (the medium) are moving permanently down the line. For it to be a wave, and it would be a longitudinal wave because you're describing compressions and rarefactions, the cars would have to drive forward, shift into reverse, and repeat!
To redeem myself from this brash attempt at being technical, check out this traffic simulator
Bam!