You seem to have forgotten to take your comment out with you.

Bio-engineer the animals so their antlers and/or fur becomes reflective itself, and / or glow in the dark.

Bio-engineer vehicles that instinctively avoid deer.

If we're doing that level of bioengineering, the other direction would be to have the vehicles be able to eat any deer that cross its path for fuel. The circle of life doesn't work without predators at the top who eventually die themselves, returning their energy to the beginning of the cycle.

Put a tiny radio on all of them that broadcasts a “deer here” signal, and require cars to have a receiver to detect them. Ideally, make it a RFID.