Negotiating legal, economic and political hazards will be far harder, for two reasons. First, they will inevitably crash into humans' warped perception of risk. Smart cars may in fact be safer as they tailgate one another at 70 miles per hour, but they will not seem that way at first. Train and airplane guidance systems collapse all the time. They will fail frequently, causing dramatic collisions, some lethal.
Most people overestimate the dangers of air travel because every accident makes the nightly news.
Glitches in a new technology will get even more intense scrutiny. Current laws would hold those who build the cars and roads liable for damages whenever system failures cause a crash, whether they had been negligent or not. In theory, Congress could limit their liability, as it did for the airline industry. In practice, tort reform is a political minefield. Certainly not the nondrivers.