‘The standard speed limit in urban areas is 30mph, which represents a balance between mobility and safety factors’. So says the Department for Transport (DfT) before going on to suggest that 20mph schemes should be considered where there is a particular risk to vulnerable road users.
The Worthing County Local Committee (CLC) of West Sussex County Council requested the preparation of a borough wide 20mph speed limit scheme which excluded A and B class and some local distributor roads but also minimised the inclusion of residential streets not conforming to ‘relevant design guidance’. The reference to design guidance is a reference to those factors which the DfT suggest should be taken into account when introducing or changing a local speed limit which is, in particular, the present traffic speed on the roads in question.
The principle aim in determining appropriate speed limits should be to provide a consistent message between the speed limit and what the road looks like. Successful 20mph speed limits are intended to be self-enforcing, that is the existing conditions of the road lead to a mean traffic speed compliant with the 20mph limit.
Research into signed only 20mph limits shows that they generally lead to only small reductions in mean traffic speeds. Signed only 20mph speed limits are therefore most appropriate for areas where traffic speeds are already low. Evidence suggests that 20mph limits reduce mean speeds by about 1mph on average. If the mean speed is already at or below 24mph on a road, introducing a 20mph speed limit through signing alone is likely to lead to general compliance with the new speed limit. This allows for the 10% or thereabouts error that is the threshold for prosecution.
The speed survey of local roads that may be included in the scheme should therefore be used to identify those roads where it is likely that the limit would be self-enforcing. When the council officials considered all the information available they realised that it would not be possible to have a borough wide scheme which also met the self-enforcement criteria. For reasons about which we can only speculate, instead of informing the CLC that their brief contained this contradiction they took it upon themselves to produce the borough wide blanket scheme without regard to the minimisation of the inclusion of inappropriate roads. The result is that almost half the roads proposed to be included will not be self-enforcing. On the map the proposed area is that coloured grey. The roads with red dots are those which do not meet the self-enforcing standard.
It is possible to use traffic engineering that is, speed humps, chicanes and other obstructive devices, to force a driver to drive at 20mph. However there have been assurances that at the present time there is no intention to have anything other than a signed only limit and traffic engineering methods are not contemplated.
There is, in any event, no budget to enable extensive engineering works to be undertaken. The signs alone will cost around £300,000. To engineer the roads would cost an additional £1.5 – £2 million pounds.
What is the point of supporting a scheme which is, in large measure, bound to fail on its own terms? Where the scheme will work it is not needed because speeds are already low, where speeds are not already low it will not work.
It takes little forethought to see that the proponents of the scheme would be perfectly happy to see the speeds fail to reduce because then there would, no doubt, be a campaign mounted to force the council into authorising the traffic engineering works that would make driving frustrating and unpleasant, and pedestrians and cyclists not significantly safer.
And that, you may think, is the point of the proposals at large. As you will see from the Road Safety page there is no sensible case to be made for a 20mph speed limit in Worthing. The desire of some is to make driving as unpleasant, difficult and frustrating as possible in order to discourage car use in pursuit of their environmental fantasies.