When there were lots of accidents in planes in the 40s/50s/60s that were attributed to pilot error, they did some research and found that even highly trained pilots made mistakes because the systems and processes were complicated enough that mistakes were easy to make. Systems were streamlined, simplified, check-lists introduced, etc, all to try and make it harder for people to make mistakes easily.
If you have a complex system that relies on people, there will be mistakes. You have to make it easier to do things right, especially if those people are the average person who has a poor standard of driving. If you're going to make a system that is constantly changing the rules, giving conflicting advice via signs that you can never trust are completely up to date, if you reduce the safety area massively (ie taking the hard shoulder and turning it to a small safety zone every mile), then things will go wrong, and we've seen people get killed.
More police, more training, etc will help (it's amazing the number of cars that navigate these road systems with no problems), but there will always be more risk when you ask people to operate these "driving systems" that are inherently prone to errors. That's been proven by actually running them in the real world.