[tomohawk]

The odds are that self driving cars will stick to the posted speed limit, and that those limits will not be raised. This will reduce the available capacity of many interstate grade roads, as the posted speed is often unsafely low. On the roads around here, the accepted and safe speed is often around 70mph, but the posted speed is often 55mph.

https://www.motorists.org/blog/speed-limits-slower-safer/

Additionally, self driving cars appear to have a higher accident rate per mile driven (5x). This appears to be at least partly the result of the self driving cars performing unorthodox maneuvers in some situations.

[nimbix]

This complete disregard for speed limits was a huge shock to me when I was driving in Florida 2 weeks ago. In quite a few EU countries we stick to the posted limits quite strictly. But in the US I was literally bullied into driving way above the limit (75 in a 55 zone) and was still getting overtaken on both sides - in one case even by a police car - and some people used turning lanes to overtake on the right. In addition to this everyone was slamming their brakes when they saw an empty police car parked by the side of the road. Crazy.

[DarqWebster]

Slower not meaning safer is because a slower driver among faster drivers causes more lane-changes, which are a less-safe maneuver. Everyone travelling the same speed is the safest scenario, with slower then being safer, as impacts occur with less energy.

If everyone strictly obeyed the posted speed limit and treated it as both a minimum and a maximum speed, as driverless cars would likely aim to do, roads would be safer. The interim state of having both driverless and human-driven cars on the road at the same time is where problems may arise.