You've asked an interesting question. I can't find a good source on what is the range of reaction times for autonomous vehicles. However, in the test videos I've seen, they appear to be human-level or better. For reference, human reaction times (to start braking) are typically between .5-2 seconds. It's difficult for humans to react to anything in under .25 seconds.

I don't think it's controversial to say that machines can easily beat those human reaction times.

Most or all autonomous vehicle software is written in C++, so garbage collection shouldn't be an issue. Of course, these programs need to be tested carefully and extremely before we trust them.