A lot of traffic accidents are due to drivers’ errors. Therefore, a certain number of accidents will decline with automated driving. On the other hand, new safety hazards could arise as the result of autonomous and connected vehicles, such as possible failure of hardware and software. Autonomous Vehicles (AVs) can provide a higher level of mobility for the disabled, elderly, and younger passengers, improving their mobility and enabling their greater inclusion in society, but they also present technical and safety challenges that must be addressed. As confidence in AVs grows, passenger risk taking may also increase. During the early stages of AV deployment, when self-driving vehicles are mixed with AVs, some drivers may attempt to join the platoons of autonomous vehicles that may be operating on dedicated lanes close together at high speeds, which could result in increased crash severity. Furthermore, autonomous vehicles and their safety impact have not been sufficiently tested in extreme weather conditions associated with snow or heavy rain.

Transportation is the framework upon which cities are built. Historically, the advent of automobiles which was an advancement in technology made some major changes to the cities. Some of the influences were good, some were bad, and some were ugly. For those cities where policies did not intervene, the higher speed encouraged residents to live far from the city centers and drive farther to work. This meant longer travel distance, more pollution and energy consumption and brought urban sprawl by the most inefficient use of resources. Urban sprawl is the manifestation of automobiles, wide and long roads, and low-density suburbs which were grown horizontally. This has also had high implications on cost to build and maintain roads. The same could happen because of autonomous vehicles, but this time, convenience and higher efficiency could encourage residents to live much farther from the city centers and exacerbate the sprawl and increase vehicle kilometers traveled (VKT), unless clear regulations and policies are adopted to manage their use. In contrast, multi-modal systems that include private autonomous vehicles, but with emphasis on autonomous transit and non-motorized transportation, coupled with policies to limit the urban growth boundary, and encourage land use density and compactness, could be very beneficial for cities.

The bottom line is, cities should be built for people and not cars, regardless of whether the cars are operated by people or autonomously. It is known that the shortened gaps and platoons coordination derived from autonomous vehicles can increase roadway capacity and therefore reduce traffic congestion, but this is half of the story. The other half that is missing is the fact that increased capacity will entice drivers who commute at the shoulder of the peak to beat traffic they would change their time of day to travel to drive at peak, also those passengers previously using other modes such as transit, walking, bicycling, or even carpooling may decide to drive using autonomous vehicles. In the prime time of freeway building in USA in the 1950s, the legendary architect and urbanist Lewis Mumford warned that “trying to cure traffic congestion with more capacity is like trying to cure obesity by loosening your belt.” Traffic is known to be like gas: as you open more space for cars, they will fill up the entire road.

AVs could have both positive and negative effects on traffic and mobility. To take maximum advantage of autonomous vehicles, policies and regulations should be in place to discourage travelers to use their convenient autonomous private vehicles by measures such as congestion pricing, limited and high-priced parking, and encourage them to use autonomous transit vehicles.

The “tragedy of commons” is an economic theory describing how individuals tend to act selfishly by depleting publicly accessible and underpriced or free resources, eventually degrading the public realm in terms of environment, energy consumption, health, and well-being. Travelers will continue to use and congest roads with or without autonomous vehicles, unless planning and policies, coupled with suitable design and land use measures, discourage private automobiles and provide incentives for public transit. Those suitable land use and urban design measures for livable and vibrant cities should be built based on new urbanism principles including higher level of walkability and connectivity; mixed use and diversity; mixed housing; quality architecture and urban design; traditional neighborhood structure diversity; increased density; smart multi-modal transportation; sustainability and quality of life.

Hamid Iravani, transportation planning director and fellows board member, Parsons