An analysis by Victoria Transport Policy Institute, Canada indicates that some benefits of autonomous vehicles such as independent mobility for affluent non-drivers, may begin in the 2020s or 2030s, but most impacts, including reduced traffic and parking congestion (and therefore reduced road and parking facility supply requirements), independent mobility for low-income people (and therefore reduced need to subsidize transit), increased safety, energy conservation and pollution reductions, will only be significant when autonomous vehicles become common and affordable, probably in the 2040s to 2060s. A few benefits may require prohibiting human-driven vehicles on certain roadways, which could take longer, writes Todd Litman Founder and Executive Director of the Victoria Transport Policy Institute.
There is much speculation concerning autonomous vehicle impacts. Advocates predict that consumers will soon be able to purchase affordable self-driving vehicles that can greatly reduce traffic and parking costs, accidents and pollution emissions, and chauffeur non-drivers around their communities, reducing roadway costs, eliminating the need for conventional public transit services (Keen 2013). Under this scenario, the savings will be so great that such vehicles will soon be ubiquitous and virtually everybody will benefit. However, it is possible that their benefits will be smaller and their costs greater than these optimist predictions assume.
Advocates of autonomous vehicles predict these will provide significant user convenience, safety, congestion reductions, fuel savings, and pollution reduction benefits. Such claims many be overstated. For example, advocates argue that because driver error contributes to more than 90% of traffic accidents, self-driving cars will reduce crashes 90%. However, autonomous vehicles are likely to introduce new risks including system failures (“death by computer”), cyber terrorism, offsetting behavior (the tendency of road users to take additional risks when they feel safer; also called risk compensation) and rebound effects (increased vehicle travel resulting from faster or cheaper travel. For example, because they feel safer vehicle occupants may reduce seat belt use, other road users may become less cautious, vehicles may operate faster and closer together, and human drivers may be tempted to join autonomous vehicle platoons – it may become a sport – which will introduce new risks and enforcement requirements. Detailed analysis by Sivak and Schoettle (2015) concluded that autonomous vehicles may be no safer than an average driver and may increase total crashes when self- and human-driven vehicles are mixed.
Estimated congestion and parking cost reductions, energy savings and emission reductions are also uncertain due to interactive effects. For example, the ability to work and rest while traveling may induce some motorists to choose larger vehicles that can serve as mobile offices and bedrooms and drive more annual miles. Self-driving taxis and self-parking cars will require empty backhauls. Although the additional vehicle travel provides user benefits (otherwise, users would not increase their mileage) it can increase external costs, including congestion, roadway and parking facility costs, accident risk imposed on other road users, and pollution emissions. Some strategies such as platooning (groups of vehicles driving close together in order to increase traffic capacity) may be limited to grade-separated roadways, so human-driven vehicles may increase congestion on surface streets. Autonomous vehicles may reduce public transit travel demand, leading to reduced service, and stimulate more sprawled development patterns which reduce transport options and increase total vehicle travel.