This resource examines how new technologies in AVs will affect traffic behavior, and how these new behaviors will impact congestion, capacity, and efficiency of road networks.

"Autonomous vehicles offer new traffic behaviors that could revolutionize transportation. Examples include reservation-based intersection control and reduced reaction times that result in greater road capacity. Most studies have used microsimulation models of those new technologies to study their impacts more realistically. However, microsimulation is not tractable for larger networks. Recent developments in simulating reservation-based controls and multiclass cell transmission models for autonomous vehicles in dynamic traffic assignment have allowed studies of larger networks. This paper presents analyses of several highly congested arterial and freeway networks to quantify how reservations and reduced reaction times affect travel times and congestion. Reservations were observed to improve over signals in most situations. However, signals outperformed reservations in a congested network with several close local road and arterial intersections because the capacity allocations of signals were more optimized for the network. Reservations also were less efficient than were traditional merges and diverges for on- and off-ramps. However, the increased capacity from reduced following headways resulted in significant improvements for both freeway and arterial networks. Finally, the authors studied a downtown network, including freeway, arterial, and local roads, and found that the combination of reservations and reduced following headways resulted in a 78% reduction in travel time."

Key findings

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"Autonomous vehicles (AVs) offer new traffic behaviors that could revolutionize city transportation. New intersection controls (1, 2) could reduce intersection delays (3, 4), and adaptive cruise control, reduced reaction times, or both could similarly increase road capacity (5, 6). However, AVs could offset these improvements by increasing travel demand. Levin and Boyles found that allowing empty repositioning trips to avoid parking costs could result in overall increases in congestion (7). Furthermore, the Braess (8) and Daganzo (9) paradoxes demonstrate that improvements in capacity could increase congestion as a result of selfish route choice."

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"Overall, the authors conclude that reservations using the FCFS policy have great potential for replacing signals. However, in certain scenarios (local road and arterial intersections that are close together and at high demand), signals outperform FCFS reservations. This outcome might be improved by a reservation priority policy that is more suited for the specific intersection. However, reservations were detrimental when used in place of merges and diverges. Because merges and diverges do not require the same delays as do signals, reservations have limited ability to improve their use of capacity. Furthermore, the FCFS policy could adversely affect capacity allocation. Therefore, FCFS reservations should not be used in place of merges and diverges, but other priority policies for reservations might be considered."

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