Speeding motorists could find it harder to avoid police detection if a scheme to introduce a hi-tech point-to-point speed camera system goes ahead.

Unlike the existing speed cameras used by police, which can only detect a vehicle's speed at a certain spot, point-to-point (P2P) cameras can calculate how fast a vehicle is travelling over a prolonged distance.

Already used in parts of Australia and across the United Kingdom and Europe, the system works by using two cameras to record images of all vehicles as they enter and exit a pre-determined stretch of road.

The time-stamped images are matched using automatic number-plate recognition software.

Each vehicle's average speed within the corridor is then determined by dividing the total distance between the camera points by the time taken to travel between them.

If the speed calculated is higher than the enforcement speed, an infringement notice can be issued.

In the United Kingdom, P2P speed cameras established on corridors with a history of high-speed crash rates have led to significant reductions in fatal and serious-injury crashes, and researchers say similar results could be expected here.

Now, in line with the Transport Ministry's "2010-2020 Safer Journeys" strategy document, which recommends the government investigate introducing P2P cameras, road safety researchers have prepared a report for the New Zealand Transport Agency on the merits of the system.

The report puts the cost of installing the hi-tech speed detection system at $1.1 million, with additional running costs of around $850,000 a year, but the researchers say the benefits would outweigh the costs.

"Safety benefits observed overseas are likely to be replicated within New Zealand on corridors that meet suitable criteria," their report says.

In the year ended June 2010, police issued more than 457,000 speed-camera-infringement notices, but there is international research to suggest spot-speed camera systems used here have limited impact in terms of modifying driver behaviour.

Although the fixed-point cameras are effective at reducing speeds at the camera site, research suggests drivers return to their approach speed within 500m of passing the camera.

"The P2P speed camera system has significant advantages over fixed-point speed cameras in that it extends the speed enforcement coverage over a greater area. P2P cameras also produce a more uniform speed profile, with driver speed compliance over the route rather than at a single point," the authority's report says.

Some legislative changes will be needed before P2P can be introduced in New Zealand but 11 stretches of road have already been shortlisted as potentially suitable sites.

But road safety campaigner Clive Mathew-Wilson questions whether introducing such a camera system would make roads safer.

"P2P cameras are unlikely to make much difference to the road toll because the vast majority of fatalities occur at speeds below the legal limit," he said.

It would be more effective to change the roads than to try to change the behaviour of motorists.

A spokeswoman for police national headquarters said the possibility of adding P2P cameras to the police arsenal against speeding motorists would be looked at "in the fullness of time", but there were no immediate plans.

Police do already have four cameras with number-plate recognition technology but they are being used to locate individuals with outstanding arrest warrants, to identify stolen vehicles, and to locate vehicles that may have been involved in illegal activities, rather than to target speeding motorists.

FAST LANES FOR SPEED TRAPS

Eleven stretches of road have been identified as potentially suitable sites for P2P cameras - with four Auckland-based locations:

Auckland's northwestern motorway from Newton Rd to Te Atatu Rd

The Auckland-Hamilton motorway, from Mt Wellington highway to Irirangi Dr

Auckland's southern motorway, from Green Lane to the southeastern highway

Auckland's southern motorway, from north of Orams Rd to Great Rd, Drury.