We would increase speed limits. Self driving cars will likely be limited by the law. Nobody wants their self driving taxi to be going 55mph when the humans are doing 80. I described this in reply to a different comment.
https://news.ycombinator.com/item?id=16475369
>Surface roads with at-grade intersections can't be sped up meaningfully, and there's no space for relatively high-speed highways, not without spending exorbitant amounts of money on building them.
Every red left or right arrow could be replaced with a blinking yellow or solid green for starters. I think we'll see laws about stop signs being equivalent to yield if turning right.
There's a lot of inefficiency baked into the system as a means to mitigate stupid people at high volume points.
For example, we don't bother stopping cross traffic for someone to take a left on solid green but we do at an intersection with a dedicated left turn lane/arrow because of volume. The volume in the latter case is high so we bother to include redundancy to protect the several people per year that would cause problems if they tried to take the left without cross traffic stopping. It's not worth it to have a lane and an arrow to protect at an intersection with a lower volume of left turns so we use a solid green and left turning traffic yields. As self driving cars decrease the number of people that wouldn't be able to take the left on a solid green or blinking yellow then we'll gradually see more of those and less dedicated turn lanes.
>If anything, the fact that humans tend to do things like drive too fast for conditions or leave too little a gap for safety means that properly safe cars will go slower than the average driver.
What's "too fast" isn't defined by us. It's defined by how people actually drive in the conditions. A self driving vehicle that drives like a student driver and gets from A to B no faster than the letter of the law allows is at a huge disadvantage. Nobody's gonna buy a car that's 20% slower everywhere and frustrating to watch operate. Nobody's gonna recommend it to their friends if they have to press the override button every time they want to pull out into traffic in a timely manner or if they're always getting honked at.
Sure, you can hand wave about it not being a problem with full adoption but you need to get to full adoption first and that requires a product that's better in at least one way and comparable/acceptable in all the rest. Look at electric cars. They didn't exist in the high end until Tesla made one that was better in a few ways and comparable in the rest.