Anecdotally, I'd say that something like 50% of the cars I see on the road are at least 10 years old. Probably 15% are 20 years old or more. I live in one of t

Anecdotally, I'd say that something like 50% of the cars I see on the road are at least 10 years old. Probably 15% are 20 years old or more. I live in one of the poorer states in the US, so my experience may be somewhat skewed. This also brings up one of my concerns with self driving cars. A vehicles (or and mechanical device) age, they become less reliable. The brake booster on my truck went out today (20 years old). I could still brake, but it took significant effort. I wonder what the failure modes look like on the self driving apparatus, and wether they fail gracefully and safely. I think it will be important that when we have 10 or 15 year old self driving vehicles on the road that they have engineered in safe failure processes.