It depends on how fast the incoming car is travelling. If you are about to be rear ended by someone traveling 60 miles an hour (happens sometimes in rural areas where people don't pay attention and are traveling highway speeds on narrow two lane roads), then it would actually be safer to accelerate the car to 30mph and crash into the person in front of you so that it is a 30mph impact to front and 30mph impact to rear rather than a massive 60mph impact to the rear of the car.