Strict speed enforcement could have a detrimental impact on road safety because drivers are dedicating more attention to monitoring their speed than detecting hazards, a study has found.

Researchers from the University of Western Australia used a driving simulator to test whether reducing the speed enforcement thresholds would impact on a driver's mental and visual abilities.

The study recruited 84 participants who were told they could be fined for driving one, six or 11 kilometres per hour over a 50 kilometre per hour speed limit, and measured their response to small red dots which appeared in their peripheral vision.

Lead researcher Dr Vanessa Bowden said the study found those who were given a one kilometre per hour threshold were less likely to detect objects outside of their immediate line of sight.

"We concluded that drivers' mental and visual resources were being used up by paying extra attention to the speed monitoring task, and this was taking some of their attention away from the visual world around them when they were driving," she said.

The participants were also asked to fill out a questionnaire which asked how difficult or demanding they found the experience.

Drivers who were given a stricter speed limit threshold rated the experience as more demanding.

Dr Bowden said road safety authorities should take note.

"There can be a perception that by making it stricter you're only going to get benefits, like you'll get everyone driving more slowly and more safely," she said.

"But ... you can't necessarily make drivers pay more attention to the speed and go more slowly without taking their attention away from some other critical aspect of driving."

Police said there was a small leeway above the speed limit in WA, but do not publicly reveal what it is.

The researchers will also investigate whether drivers respond poorly to hazards when strict speed limits are enforced.