Multiple warning signs to motorists of mobile speed cameras ahead and their use in limited locations have hampered their ability to improve road safety in NSW, the Audit Office says.

While the 30 “best-performing” mobile speed camera sites have led to a reduction in fatal and serious crashes, a report by Auditor-General Margaret Crawford found limited evidence cameras have led to a change in driver behaviour across NSW by acting as a deterrence.

The Auditor-General says the warning signs limit the ability of cameras to act as a deterrence to motorists speeding. Credit:Jane Dyson

The state has had an overall reduction in serious road injuries but the number of fatalities involving speed soared by 19 per cent in the 12 months to April. Speed is a factor in 40 per cent of fatal crashes in NSW.

In a report released on Thursday, the NSW Auditor-General found that multiple warning signs of speed cameras ahead have reduced the likelihood of them acting as a deterrence across the road network, which is their main purpose.