The risk to toll roads if autonomous vehicles to take off quickly, is that there will be less congestion, less traffic and less vehicles past their gates.
Personal ownership of vehicles drops dramatically as you move into city centers, autonomous vehicles means that vehicle efficiency and thus the price to charge passengers per ride etc will in all likelihood drop further. Whether Uber, Taxi's or whatever they end up being called .. you wont need to own a car if you can dial up a ride on demand. If there are no drivers, the standy costs will be lower and potentially there can be more capacity both on the road - but also waiting in the wings for being called to action when needed.
Its bad enough being a taxi driver and paid less than $10 an hour to get not much work. Thus there is no incentive to sit around if you get paid less and less (whilst I acknowledge that many still do). The lower the standby cost, the more incentive for companies to have vehicles available and potentially more dispersed than taxi's currently are.
Looking at other transport technologies, whether commercial aviation, trucking etc and the vast improvement of efficiency and reduction in cost once you automate the routes, deliveries and improve their utilisation.
Once you do the same for passenger and small goods transport, the cost will come down which will likely mean less vehicles driven places because people want the convenience of a 'car at the other end' or by virtue of there simply being no taxi or public transport in the area.
(20min delay)