The Impacts of Reallocating Roadspace on Accident Rates: Some Initial Evidence

Sally Cairns

As requested, this note reports on evidence about the impacts of reallocating roadspace on accident rates, which has been drawn from a major project about reallocating road space. The main project was focused on the impacts of reallocating road space on traffic volumes, although some data were collected about the safety implications. This note provides an initial analysis of that data.

Logically, the relationship between reallocating road space and accidents could be complex. On the one hand, traffic reduction and greater priority for other modes suggests that buses, cyclists and walkers should benefit from less conflict with other modes of transport. However, there could be various offsetting problems. For example, there could be additional accidents on diversion routes; more aggressive driving styles could be dangerous; vehicles pulling in and out of bus and cycle lanes might lead to problems etc.. These hypothetical arguments can be addressed by looking at the evidence.

In the majority of cases of planned road-space reallocation, improvements to safety are often one of the objectives, or even the prime reason for putting in the scheme. For example, private traffic was originally excluded from Oxford Street in 1972 because it was the worst accident blackspot in London, and probably the whole of Britain, with 265 personal injury accidents per annum. Similarly, prior to closure, Princes Street in Edinburgh was witness to 108 personal injury accidents p.a..

Once schemes had been implemented, there were often references to a difficult adjustment period. For example, there were initially problems with the Sheffield Supertram, where one cyclist died after getting his wheel stuck in the tracks, and many car drivers experienced problems because the tracks were slippery to drive along.

We were sent 8 case studies with results of proper accident evaluation. These can be summed up as follows:

Figure 1: Change in accident rates after roadspace reallocation

Case study (+ time after implementation)

Overall % change

Additional details
London: Oxford Street + diversion area (5 months)


Section of major shopping street closed to private traffic. 50% reduction in fatal and serious accidents, offset by an increase in minor accidents
Norway: Street Enhancement Programme (1 year forecast)


The major streets through 5 towns were redesigned to reduce the dominance of traffic. Accident reduction forecast varies by town, and has been predicted from detailed analysis of observed changes in vehicle speeds. Overall estimated saving of 4.2 million NOK p.a
London: Ring of Steel, City of London

(30 months)


Traffic redirected to a box of roads around the core of the city, and entry to the core of the city restricted. 39% accident reduction in the core area, and a 10% reduction in the box of roads around the core. Overall saving of £3.5 million p.a..

Princes Street

(1 year)


Private traffic excluded from eastbound section of the shopping street.

Information unavailable for all diversion routes. However, 3 months post-closure, accident monitoring on major diversion routes of George Street, Charlotte Square and Queen Street did not show any increase in accident rates.

Gothenburg CBD

(12 years)


Traffic cells introduced. 45% accident reduction within the cells.

(2 years)


Traffic cells introduced. 27% accident reduction within the cells, 9% reduction in the roads around the cells. Overall saving calculated as 2.2m SEK p.a..
Hamm (1 year)


Major road into Hamm reduced from 4 lanes to 2.

Orpington High Street (10 months)


Private vehicles excluded from entering the shopping street 10am-4pm.

Change in accident rate refers to 24hr rate, although most of the reduction occurred during the closure period.

No information available about diversion routes.

London: Partingdale Lane + diversion route

(8 months)


Closure of narrow country lane


There are various problems with interpreting the data. For example, the last two percentages relate to only small changes in absolute numbers of accidents (about 10 p.a. pre-closure for Partingdale lane, and about 7 p.a. pre-closure for Orpington High Street).

Local authorities also often highlighted that they had, say, three years of before data but only a short period of after data. For example, the Oxford Street results only refer to 5 months after entry for private traffic was restricted, and the authors commented that it was ‘too early’ to say definitely what the impacts were, particularly as the results reflected teething problems at one junction where there had been 14 accidents in three months. The junction was reconfigured as a result, and a reduction of 26 accidents a year was expected in the long term. Unfortunately, we were unable to obtain any later reports, to check whether this had happened.

In terms of impacts over time, Gothenburg is perhaps the most informative. In Gothenburg, a series of traffic cells has been developed. Traffic has been rerouted to roads around the edges of each cell. Meanwhile, within the cells, priority has been given to modes other than the car. This has been done in two phases, with cells created first in the central business district and second, in the surrounding central urban area (CUA). Hence, the reduction of 40% per annum from the CBD results from 12 years of having the cells, whereas the 14% per annum reduction was observed after only two years, and the authors comment that greater reductions are expected from the CUA zones in the future. Gothenburg also has a policy of changing the land-use of the roads which go around cells, which should further enhance safety.

In terms of the other case-studies - the Ring of Steel in the City of London is a similar case to Gothenburg, where the spatial separation of vehicles and people has helped to reduce casualties. With Princes St and Orpington High St., the savings have come from traffic reductions on those main shopping streets due to entry restrictions for private vehicles, whilst in Hamm, Partingdale Lane and the Street Enhancement Programme in Norway, most of the savings have come from reductions in the speed of the motorised vehicles.

In brief, the initial impression from the evidence is that there are a number of cases where there have been significant reductions in accidents as a result of well-implemented schemes to reallocate road space. There is further scope for obtaining information on these (and other) case studies, and presumably, data are also available from more specific projects to assess the safety implications of implementing light-rail schemes, bus lanes, cycle lanes and pedestrian areas. We would welcome any contributions of evidence from those who are working on the topic.

Note from Road Danger Reduction Forum conference, Leicester, 16th February 1999.