Do we have need to have speed humps?
The DfT guidelines indicate that traffic signing can be the only measure required, and traffic calming such as pinch points or speed humps may only be needed if traffic tends to be going much faster. Traffic signs can include painted marks on the road, which in one Oxford area were designed by the local residents. The removal of double yellow lines with more on-road parking may also be used to slow traffic – see Knebworth’s high street for one example of that.
Evidence from Bristol suggests that 20 mph limits, without ‘physical measures’ such as road humps, can achieve significant speed reductions – from 31mph to 26 mph. This can be regarded by traffic engineers as insufficient as a scheme is rated as successful if mean speeds of 24mph have not been reached, yet the severity of injuries sustained in collisions at the lower speed are significantly less. Other evidence at the Scrutiny Committee showed that this speed reduction would halve the number of fatal accidents. The Bristol experience showed that 20 mph speed zones reduced speed on 65% of roads. This was popular – community support for the zones was 70% before its introduction and 89% afterwards.
But, what about slower journeys and fuel consumption?
Even though a journey of one mile across Hitchin would take one minute longer at a steady speed of 20mph rather than 30mph, journey times are overall helped by traffic moving more smoothly. At slower speeds it is easier for traffic to merge into the stream of cars, reducing the back-up of cars on contributory roads. Also at slower speeds there is less braking and accelerating, which improves fuel economy.
How will a 20mph speed limit be enforced?
The police force’s attitude to the speed limits is important, but the wrong impression has been generated. It was thought that they would not and could not enforce the lower speed limit. It is stated in various places that the lower speed limit should be self enforcing – ie. people would not want to, and probably could not due to road conditions, exceed the speed limit. This is clearly not the case on many roads which have 30 or 40mph limits now, but it seemed that extra engineering to slow traffic could not be introduced to help slow traffic. What was made clear at the Scrutiny Committee was that no extra policing could be expected, but the police would respond to local concerns, as they do now, and speed surveillance on specific roads agreed at ‘Local Priority Setting Committees’ (although it was uncertain whether these were operating in all towns). Chief Inspector Richard Hann also mentioned the Community DriveSafe scheme, by which volunteers can become involved in monitoring traffic speeds in their community – click here.
There has been reliance by the police forces on the guidelines from the Association of Chief Police Officers (ACPO), the latest revision coming on October 11th – click here. This introduced the use of speed awareness courses for drivers driving between 24 & 31 mph in 20mph zones.
Rod King, for the national 20’sPlenty campaign, put another emphasis – on compliance rather than enforcement, suggesting that by engaging people with education about the benefits, and generating enthusiasm for the change, the message will spread and people will accept and support the lower speed limit. From experience elsewhere it seems that speeds are often reduced in surrounding areas as the culture or habit of driving slower catches on. The 20’sPlenty recent briefing summarizes the ACPO position – click here.