CAVs are expected to decrease congestion up to 50 percent, increasing the effective capacity of urban networks leading to a new equilibrium with more users but with negligibly less congestion than the current system.

A simulation model found that many of the direct benefits of connected and automated vehicles (CAVs) would be mostly or greatly offset by the resulting changes in traveler behavior, indicating an overall neutral impact on cities.

Date Posted

Implementation of Connected and Autonomous Vehicles in Cities Could Have Neutral Effects on the Total Travel Time Costs: Modeling and Analysis for a Circular City

Summary Information

A modeling experiment by researchers from the University of Santiago, Chile and the Technical University of Catalonia sought to understand the impacts of Connected and Automated Vehicle (CAV) adoption in urban spaces.

The mathematical model, based on a theoretical circular city structure, incorporated various projected impacts of CAV usage. These included a lowering of travel-cost, given the increased freedom of CAV users; increased average speeds and road capacity, given CAVs' platooning capabilities; and a decrease in operational costs, because of CAVs' increased fuel efficiency. The model used continuous approximations to understand the impacts of CAV adoption, considering simulated demand zones across the city.


The model found an array of direct effects of CAV adoption, which were positive for the city, and indirect effects, which served to largely counterbalance the benefits.

Some of the key direct effects included:
  • Reduction of costs. As a result of the decreased congestion, and because of more efficient operation, CAVs were projected to decrease operation cost by about 30 percent compared to manually operated vehicles.
  • Reduction of road congestion. The ability of CAVs to drive cooperatively resulted in congestion reductions of between a third and half the congestion incurred by manually operated vehicles.
The indirect effects included:
  • Induced demand. Although CAVs will reduce the cost of congestion, this impact will result in more users entering the system. This ultimately results in a new equilibrium that has only negligibly less congestion than the current system.
  • Increase in Vehicle Kilometers Traveled. Although CAVs would be able to provide more efficient door-to-door service for passengers, the vehicles will still need to travel on the road without passengers. When accounting for the increased number of users on the road, this will result in a significant increase in VKT.
The researchers analyzed the overall impact of CAV adoption by examining the total cost to users and agencies, as well as the total congestion level. Both were analyzed for various rates of CAV market penetration. The model found that while the total cost fluctuated for different values of market penetration, it overall decreased as penetration rates increased.

However, the analysis also found that congestion could increase relative to the current system for middling values of market penetration--particularly when between 20 percent and 50 percent of vehicles are automated. This suggests that agencies seeking to promote CAV adoption should anticipate that negative results could arise during the process of transitioning from manual to automatic vehicles. The increase in congestion is expected to be completely outweighed by the point of 70-80 percent CAV adoption, for a significant overall increase in efficiency.

On the whole, the mixed results from the analysis indicate that CAV adoption--which is likely to take a significant amount of time--will not be a unilateral benefit to cities, and in fact many of the positive changes will be mostly or completely offset by changes in traveler behavior.