The most reliable car detection is by induction loop in the tarmac. It'll detect any big hunks of metal basically, regardless of the weather, rain and snow, whatever. It will work. You'd need a link (wireless makes most sense) between the point where you want to detect the car and the camera.
I don't see an easy way of detecting a car from 100m distance. LiDAR doesn't normally get that far.
pathfinderwy:
2. Not sure if mechanical vs electronic trigger...how is a DSLR Nikon camera triggered?
I'd suggest you have a good look at your camera, and check the manual of it on how to trigger it. That link is obviously an electronic trigger.