LOCAL AUTHORITY efforts to improve road safety by inserting speed humps on city streets risk increasing pollution instead, according to a report published this week by transport research body TRL.
The speed humps, or so-called 'sleeping policemen', can cut traffic speeds by between 6mph and 12mph and reduce accidents by between 30% and 60%.
But the obstacles force traffic to speed up and slow down between humps and this can result in increases of between 20% and 60% in hydrocarbon and carbon monoxide emissions.
Nitrogen dioxide emissions from diesel vehicles can also increase by as much as 30%, says the report.
Speeding up and slowing down also causes vehicles to expend more energy than they would if travelling at a continuous speed, resulting in increased emissions.
However, the report says that although traffic calming can increase emissions from individual vehicles, traffic flows reduce on roads with speed humps. As a result the total effect of speed humps on air quality is unknown, says the report.
The report also confirmed that emergency vehicle response times were not significantly affected, unless a whole series of traffic calming areas had to be negotiated en route to an incident.