Eventually, I expect we'll have some national standard for wireless transmitters on traffic signals, so they can send a message (timestamped and cryptographically signed with the state's department of transportation's public key) to the cars to tell them unambiguously when to stop and when it's safe to go.

(This could help human drivers too; just add a red/yellow/green light to the car dashboard for those times when you can't see the actual light because there's a big truck in the way, or the sun is directly behind the traffic signal.)

I also expect that by the time this sees near-universal adoption, we'll already have the image recognition corner cases mostly worked out.