Forget front and rear bumpers. If automobiles could incorporate a little Star Trek technology, there would be far fewer traffic accidents.
In the fictional realm, shields are typically made of energy or charged particles used to deflect energy, ballistic weapons, and natural galactic bodies. But they can only repel so much damage. After repeated attacks, shield strength is often exhausted, and damage becomes unavoidable.
It seems unlikely that a force field would be able to prevent collisions altogether; more likely would be a barrier that might soften a blow, protect against particle damage from rocks or insects, and take the guesswork out of parking in tight spaces.