The City Centre 20mph zone

This article was published in 2005, in Newsletter 60.

A 20mph zone is planned in the historic city centre. Cambridge Cycling Campaign strongly supports the plan but would like the zone to be larger and more clearly defined than the one the County Council is at present proposing.

The case for such a zone was made in an article in Newsletter 59 (‘Road Speed Reduction in Cambridge‘). The argument is simple: 90% of people hit by a vehicle at 40mph die, 20% at 30mph and only 2.5% at 20mph. Low speeds greatly reduce both the severity and the frequency of collisions. Any driver, even if very skilled and experienced, can make mistakes. The consequences of an error are much more likely to be serious when driving at more than 20mph in areas with high densities of pedestrians and cyclists.

Current city centre speed limits are confusing and poorly understood. In Bridge Street, Emmanuel Road and Silver Street a 20mph limit is used to protect short lengths of roadway where there are rising bollards. Everywhere else the limit is 30mph except between 10am and 4pm when those few vehicles permitted into the heart of the city are restricted to 10mph. (The 10mph restriction during this six-hour period is not controversial and would remain.)

County Council officials have put forward a new scheme which would incorporate the three short lengths of 20mph road into a wider city centre 20mph zone. Such a scheme should improve road conditions for cyclists as well as pedestrians. It should also, for example, help us in our current campaign to secure a cycle contraflow in Corn Exchange Street. We have two problems with the County’s proposal. The first is that their zone is too small. The second is that its boundary is jagged and complex. We believe that the limit is far more likely to be observed if its boundary is straightforward, coherent and easily remembered.

Map showing County Council's proposed 20mph zone and Cycling Campaign's preferred plan

Our zone would be the area within the ring defined by the following roads: Chesterton Lane, Chesterton Road, Victoria Avenue, Maid’s Causeway, Newmarket Road, East Road, Gonville Place, Lensfield Road, Fen Causeway, Newnham Road, Queen’s Road, Northampton Street. None of these boundary roads themselves would, however, be within our proposed zone. The main difference from the zone proposed by the County Council is that the following roads would now be included: the whole of Trumpington Street, the whole of Regent Street, Parkside, Park Terrace, Burleigh Street/Fitzroy Street and the many small streets in the Kite area, King Street, the whole of Jesus Lane, Malcolm Street and Manor Street.

The scheme drawn up by County Council officers was discussed by councillors at a meeting of the Cambridge Environment and Transport Area Joint Committee on 18 April. All were in support of a 20mph zone and a number raised our suggestions for enlarging the area and making it more logical. County Council officers expressed their willingness to consider including King Street and the streets in all or part of the Kite area. But there is, for them, an obstacle over the inclusion of some of the other streets that we have suggested, such as the part of Trumpington Street between the Royal Cambridge Hotel and Peterhouse.

The obstacle is the County Council’s speed limit policy introduced in October 2000 ( This states, ’20mph limits will only be introduced in association with self-enforcing speed reduction measures. Self enforcing means speeds being generally around 25mph or less.’ However, ‘The County Council may also introduce reduced speeds as part of accident remedial schemes or in association with other schemes, such as Safer Routes to School.’ The criteria for reducing limits to 20mph are more rigorous than those for reductions to 40mph and 30mph. We think that the County’s criteria are out of line with current analysis and current national accident data and that it is time for them to be reviewed. We understand that a reason for the present criteria may be the past reluctance of the police to enforce 20 mph speed limits.

Local officials interpret the requirement for self-enforcement to mean that if more than 15% of vehicles in a particular street are driven at more than 25mph, then a 20mph speed limit should not normally be introduced without traffic-calming measures to reduce speeds. Traffic-calming schemes can be both costly and unpopular, both factors which delay or even defeat them.

But even in terms of current policy we consider that our suggested zone meets the criteria. The County Council have carried out speed checks on many of the roads within the city centre. As I have explained, to meet the criteria 85% of vehicles have to be travelling at around 25 mph or less. All the roads checked within the Council’s proposed zone apart from Tennis Court Road meet the criteria. However, Tennis Court Road would be traffic calmed if Core Stage 4 is implemented and this would bring speeds (which are in any case only 3mph over) within the limit. For our proposed zone, Park Terrace is just outside the limit (2mph over). But it is possible that some of the so far unchecked streets within our zone might also fall just outside the limit.

The County Council’s policy also requires that ‘any zonal limits are introduced in clearly defined zones’ (AJC, 18 April 2005, Agenda Item 3a, paragraph 2.1). Our proposed zone is clearly defined. The County Council’s is not. We suggest that to achieve a clearly defined zone which people will understand, it is reasonable to interpret the policy as meaning not that every street within the zone meets the criteria, but that the great majority of them do and the residue almost do.

We do however feel that the policy which states that a 20 mph speed limit should be self-enforcing is strange and should be reconsidered. Speed limits are surely needed to achieve new standards of driving behaviour, not simply to label existing behaviour or behaviour constrained by traffic calming. Camera enforcement could now easily secure compliance if politicians and the police were ready to use it more widely.

“There is hope for a wider 20 mph zone in the long run.”
Image as described adjacent

There is hope for a wider 20mph zone in the long run. The County Council officers’ report states, ‘One of the original aspirations of the Core Traffic Scheme was to introduce a 20mph speed limit across the whole of the Core Area to improve safety, particularly for pedestrians and cyclists.’ As the Core Scheme is expanded and speeds are reduced, the officers’ suggestion is that ‘in time the zone could be expanded to cover the entire Core Area.’ The ‘entire Core Area’ is a wider area than the one we are now proposing. We share the hope for an eventual larger 20mph zone and would like to see this implemented soon rather than in the distant future.

James Woodburn