I actually don't think that's a bad idea... Specifically, most cars can only brake at about 1 G, and if that's insufficient, they use crumple zones and airbags which brake at far more than 1 G.

If emergency braking could use an explosive-spike-in-ground deceleration at say 5 G, then far more crashes would be survivable.

I think the reason it hasn't been done are human reasons - users don't like the idea that jabbing the brake pedal hard will mean they have to pay tens of thousands of dollars to repave the road and replace their spike.