Impact of CAVs on road network probed

Connected and autonomous vehicles (CAVs) could increase road capacity, and  cut congestion when incidents occur on the network, says a new report. 

Consultant Wood used PTV’s microsimulation software VISSIM to simulate the impact of CAVs on a section of the A13 in east London. The study included modelling a broken down vehicles occupying one lane for 45 minutes, which forced vehicles to use the other two lanes.

Values for reduced CAV headway distance and the distance over which CAVs communicate were based on previous tests carried out by PTV. Wood says they were not calibrated or validated and “should not be treated as standard parameters for autonomous vehicles”.

“The results indicate that switching all traffic from non-autonomous to CAVs under normal conditions (no incident) reduces average delay by 55 per cent and increases average speed by 25 per cent,” Wood reports. “This is mainly due to the reduced headway (following distance) between CAVs. It is assumed that autonomous/connected vehicles will be more efficient and make better use of road space.  43 per cent more vehicles can enter the network  with CAVs.”

Modelling of a broken down vehicle incident produced an average delay 58 per cent lower in a scenario with 100 per cent CAVs than with 100 per cent standard vehicles on the network. 

“This is mainly due to a combination of reduced headways and Car2X (vehicle-to-vehicle communication) capability of the autonomous vehicles,” says Wood.

A sensitivity test for the incident scenario assumed a 50 per cent uptake of CAVs. The results showed average delays 15 per cent lower than the base case (no CAvs), speeds 6 per cent higher, and 17 per cent more vehicles entering the network. 

“It should be noted that this is a simplified test, which does not allow for traffic reassignment resulting from early warning messaging systems,” says Wood.