How many people in the US are buying car parts online and fixing their cars themselves?

I am curious as to how many people domestically are buying individual car parts online and fixing their cars (or having the part and car brought to a service center) rather then bringing the car into a dealer or service center (paying for both parts and labor @ the shop price).
Can anyone give me [...]

How should two cars turning left in open intersection place themselves?

When the different directions are separated except at the intersection and there’s no stop sign, what are you supposed to do if both cars wait in the middle to turn left…and end up blocking each other’s view ?! How should the cars place themselves? The other car always goes to his side of the middle [...]