Watching you, watching the motor accidents

TRANSPORT researchers have devised a unique experiment in an effort to throw light on "rubbernecking" - the phenomenon of car drivers slowing their vehicles and turning their heads in morbid curiosity when they pass an accident.

The work at Leeds University's Institute for Transport Studies uses a sophisticated driving simulator and aims to produce a computer model that will allow traffic controllers to predict how an accident on one carriageway might affect traffic flow on the opposing carriageway.

"When you get an accident on one side of a dual carriageway, drivers on the other carriageway slow down to have a look," says Andrew Parkes, one of the project's supervisors.

"The problem is that people slow down much more than is necessary in terms of avoiding the car in front. This not only makes the motorway inefficient, but there is a lot of anecdotal evidence that accidents on one side of a carriageway can indirectly cause accidents on the other side."

A car slowing down excessively can set up a "longitudinal wave" of increasingly sharp deceleration down the queue of traffic, sometimes termed a shock wave or the ripple effect. This can force drivers towards the end of the queue to apply full emergency braking, with inevitable consequences.

Alternatively the rubbernecking driver might not be aware that the car in front has slowed down and can run into the back of it.

This is confirmed by Chief Inspector Paul Austen, of the Central Motorway Police Group in Birmingham. "I have to say it is a real phenomenon - it really does happen. Around Birmingham we have got some of the busiest motorways in Europe and what we find is that when there is an incident on one carriageway you actually get worse congestion on the opposite carriageway because of the rubberneckers.

"You can also guarantee that if you have one shunt on one side you will get one or two on the other side. We always send a car to both sides of the carriageway in anticipation."

The university's driving simulator - a production model Rover 216GTi sandwiched between two screens upon which computer-generated scenes can be projected - allows research student Chih Wen Fang to monitor the rubbernecking behaviour of volunteer drivers.

The volunteers, who have not been told the nature of the experiment, drive along a simulated motorway and are presented with a variety of scenarios. These include major incidents on the opposite carriageway, complete with a fleet of emergency vehicles and blue flashing lights, to minor prangs on the hard shoulder.

Tiny video cameras trace any lateral head or eye movement by the volunteers. The speed and lateral movement of the vehicle is also carefully monitored.

"When we have collected sufficient data we want to see if it is possible to identify particular patterns of traffic flow for a given set of circumstances," says Frank Montgomery, a senior lecturer in transport engineering at the university.

The ultimate aim is to produce a computer model that can be used by traffic controllers to predict the effect of an incident on the flow of traffic on the opposing carriageway, enabling appropriate action to be taken. Alternatively, a particular change in the pattern of traffic flow might signal that an incident has occurred, enabling the emergency services to be alerted.