Autonomous vehicles ‘could weaken case for roundabouts’

ROAD SAFETY

Roundabouts could be replaced by signalised junctions in a world of driverless cars, according to a new report on the road safety implications of connected and autonomous vehicles. 

“Some [crash] countermeasures currently popular because of the protection they provide to car occupants, for example, roundabouts, may become less necessary, thereby removing the heightened risk that some intersections provide, for example, to cyclists,” says the report, funded by the European Road Assessment Association (EuroRAP), the UK’s Road Safety Foundation, and the International Road Assessment Programme (iRAP).

The report focuses on transitioning to the most advanced level of autonomy – level 5, in which vehicles do all the driving tasks under all conditions, but many of the points raised are relevant to lower levels of autonomy.  

Author Steve Lawson of iRAP says the greatest crash risks for conventional vehicles on inter-urban roads involve running off the carriageway, head-on collisions, intersection collisions, and shunt crashes.

“This is likely to change with the introduction of AVs as lane-keeping technology, enhanced road positioning, speed management, vehicle-to-vehicle connectivity and autonomous emergency braking comes into play.

“Some current crash countermeasures may be needed less in the future than they are now,” he says. “For example, barriers may be required less and the economic benefits of roundabouts over signal-controlled crossroads may be diminished.”  

The transitional period to a full AV fleet will present new crash hazards, he suggests.  

“An AV, programmed to be cautious, slowing down at a roundabout or give-way priority intersection may stop, whereas a driver of a following conventional vehicle may believe entry is safely possible and speed up, thereby risking a rear end shunt.

“The actions of AVs to avoid birds, other small animals or indeed large plastic bags, are also noted as an issue that may impact on following conventional vehicles.

“An AV emerging from a minor road, turning left (using a drive-on-the-right convention) across a busy traffic stream of conventional vehicles would be unable to rely upon the eye contact that may often be a means of gaining permission to enter the intersection.”

He suggests that, in the transition period, countermeasures for crashes involving conventional vehicles, but also benefitting other road-users, “may also become more difficult to justify economically unless they also benefit AVs – for example, street lighting or anti-skid surfacing”.

With the growth of AVs, road maintenance, and particularly maintaining road signage and markings, will become more important. “Worn out road markings are easily missed by AV detection technology and could lead to crashes.”

EuroRAP chairman Ferry Smith said: “The transition to universal use of autonomous vehicles will, at best, take decades. What we do know is that in the transition, and probably beyond that period, roads that cars can read – through good and consistent signing and lining – will be essential, as AVs at various stages of transition, and drivers of vehicles without an autonomous function, continue to rely on them.”