RAC survey shows big safety gains with average speed enforcement

Cheaper and easier communications are providing authorities with new options for influencing driver behaviour.  Colin Sowman reports.

It’s official; Average speed cameras (ASCs) cut the number of fatal or serious injury crashes by more than a third. That is the finding of a survey by the independent 4961 RAC Foundation, the research arm of the UK motoring organisation, which looked at the outcome of installing ASCs on more than 50 sections of roads.

The survey, undertaken for the RAC Foundation by 5227 Road Safety Analysis, used data from official government sources. After excluding sites where other changes occurred at the same time the cameras were installed, the researchers were left with 25 ASC sites covering almost 300km (183 miles). After further analysis to remove statistical aberrations such as ‘regression to the mean’ and ‘national trend’, the survey concluded that installing ASCs reduces fatalities and serious injuries by an average of 36.4% with a smaller, but still significant, fall of 16% in personal injury accidents.

All of the fully analysed sites were fitted with camera systems from 79 Jenoptik, which was first into the market and has now been joined by 4080 3M, 189 Siemens and 113 Redspeed International. In the UK, the rate of implementing ASC installations has increased rapidly, partly because the cost has fallen dramatically which is mainly due to developments in communications technology. Early installations relied on fixed wiring and cost £1.5m per mile ($1.8m per mile) but this has dropped to about £100,000 per mile ($123,000 per mile) through the use of mobile communications technology and increased competition among the equipment suppliers. 

Perhaps the most significant outcome of recent installations is that average speed cameras change drivers behaviour in a way that spot speed cameras have never managed. Once spot speed cameras were erected, local drivers (and those with satellite navigation) either learned or were notified of the location of the cameras so many slowed to the posted speed as they approached the camera sites only to speed up again once out of range.

Not only did these drivers continue to exceed the posted speed limit between cameras, but harsh braking as they approached a camera location was, itself, the cause of a number of crashes as well as congestion. In some instances, this behaviour caused an overall rise in crashes and was seized upon by the anti-speed camera campaigners. 

With ASCs, this behaviour is reversed because both local drivers and those with sateliite navigation systems know a road has average speed enforcement meaning the majority stick to the speed limit, removing the need for harsh braking when approaching a camera location. 

To calculate the average speed, the exact location and distance between two or more cameras is accurately measured. The time a vehicle takes to travel between the two correlates to their average speed. The A9 in Scotland is a good example. With 112 cameras on 56 distinctive yellow columns spaced along 220km (137 miles) of often remote highway between Dunblane and Inverness, it is Europe’s longest average speed enforcement zone. While the scheme is included in the RAC’s wider analysis, changes to truck speed limits at the time the ASCs were installed, exclude it from being one of the 25 sites used in the final safety-gain statistics.

Instead of needing hard-wiring between the pairs of cameras and from the cameras to the control centre, mobile communications technology is used to relay data back to the control room, this leaves the operators the freedom to decide which cameras are active and in which configuration.  

“Each camera is programmed with its sequence number and uses 3G or 4G communications along with GPS to pick up a location and time signal. Captured information is quickly encoded and sent, along with the vehicle’s registration details, back to a central server,” says Geoff Collins, Jenoptik UK’s sales and marketing director.

Only when the encrypted registration plates are matched and the time signals are compared in the control centre does it become evident if an offence has been committed. This is much faster and easier to achieve than visiting rural sites to download the information – or even collect film for processing. Where an offence has been committed an ‘evidence pack’ containing encrypted details of the vehicle and offence(s) can be instantly transmitted to the police. Plate details and images that are of no interest are soon deleted and overwritten, so motorists’ movements are not routinely logged. 

One of the biggest benefits of ASCs is that they change driver behaviour. The old trick of speeding between spot speed sites and braking sharply when approaching a camera location no longer works. In the RAC report the distance between paired cameras ranged from 390m to 46km (28.5 miles) and with ASCs drivers do not know which cameras are active and what configuration is being used.

Short of stopping altogether, a driver who has exceeded the speed limit for any distance will not be able to reduce their average speed in the last 300m of the section-end camera. This brings about the favourable changes in driver behaviour that spot speed failed to deliver, with most drivers travelling smoothly throughout the monitored zone.

This is evident from the mid-point figures from the A9 Safety Group which show that the proportion of vehicles exceeding the speed limit is now 1 in 10 compared to the benchmark of 1 in 3. Furthermore, the proportion of vehicles being driven at more than 16km/h (10mph) above the speed limit has reduced dramatic from 1 in 10 to 1 in 250. Overall traffic volumes have increased by 6% since the cameras were installed, yet only an average of 13 drivers per day are considered for further action by the police and, most importantly, the number of fatalities has dropped by one-third.

This is fulfilling the aims of the A9 Safety Group which states on its website: We don’t want your money; we do want you to comply with the speed limit and in doing so improve safety.

When hard-wiring was the only option, instrumentation over such a distance and terrain would have been unthinkable - but now all that is needed is a power supply.

“That’s the beauty of combining average speed and mobile communications; you can position a camera almost anywhere.

Instead of needing to run power and communications cables to the camera, you can position the camera where the power is available and use mobile phone technology and GPS to do the rest,” says Collins.

“With spot speed you have to position the camera at the location where the speeding is a problem; with average speed you can place the cameras either side of the blackspot wherever there is a convenient power supply. Communications technology will take care of the rest and, as a result, motorists are more likely observe the posted speed limits over a much longer section of road, instead of charging towards the camera before braking rapidly.”

And as the power consumption of electronic systems reduces all the time, in many parts of the world these installations could be battery-powered stand-alone units with solar recharging.

Average speed enforcement systems use ANPR in order to identify vehicles, using integral infra-red illuminators to image the plates when it is dark. However, in order to capture overview or context images in the hours of darkness, additional infra-red flood lights allow for good scene images to be captured, even when the road appears to be completely dark.  This is a particular benefit for the A9 in the Cairngorms National Park. This has ‘dark skies’ status, and in such areas a visible flash or dazzling pool of white light could prove a major distraction for drivers.

Mobile communications also make the measuring of average speed across a network of roads, or even a town, much easier regardless of the number of entry and exit points. Hard-wiring a host of individual cameras would be highly disruptive and prohibitively expensive but with mobile communications that cost is slashed to little more than the hardware purchase.

The terrain and ambient conditions can affect mobile communications so the system has to be designed to cope with temporary losses of connection. On the A9 which rises to 350m (1,159ft) above sea level as it skirts the Cairngorm Mountains, the cameras have a data storage facility to hold the encrypted information in the event of a communications outage which can then transmit it when the connection is restored. Any long-term failure of communications is highlighted in the control room. And, as all cameras use the same GPS time signal, the time taken to drive between two points can be directly calculated from the timestamps and is not dependent on when that data arrived at the control room.

For authorities looking to replace ageing spot-speed cameras, serious consideration must be given to moving to an average speed system that could bring about changes in driver behaviour over a much wider geographical area.

Signal to signals

Following a fatal crash close to a signalised junction on the A78 in the Scottish village of Fairlie, traffic surveys identified that drivers regularly exceeded the 50km/h (30mph) speed limit.

505 Transport Scotland’s operating company for the area, Scotland TranServ, consulted Clearview Intelligence about ways to reduce the speeding and change driver behaviour. The result is the UK’s first scheme where existing traffic signals are used to slow speeding drivers.

The system uses wireless magnetometer vehicle sensors positioned in both lanes at between 136m and 144m from the stop line in order to detect the speed of approaching vehicles.

This information is relayed to speed-activated warning signs and the traffic signals. When a speeding driver is detected, the traffic lights are programmed to turn red in order to stop speeding vehicles and increase the journey time to beyond that realised at the posted speed.

The partners worked on the complex operational configurations to ensure that triggering the traffic lights to turn red did not create a danger to road users or pedestrians.

So instead of installing speed enforcement and penalising errant drivers, the scheme aims to influence their behaviour positively.