The Strategic Framework for Road Safety, published by the Department for Transport in May 2011, outlined a series of national key outcome indicators that measure fatality rates per billion vehicle miles as well as local indicators that measure performance against casualties who were killed or seriously injured (KSI). These indicators use a baseline of 2005 – 2009 and simply compare performance in the most recent year against this benchmark.
Although they are not described as targets, the indicators could be seen as a measure of performance by Government and the public. The Department has indicated an intention to support them with additional measures such as a local comparison website, but a lack of tangible progress has seen recent criticism from the Transport Select Committee and other road safety stakeholders.
In 2011 RSA published a suite of 116 maps showing differences in performance between local authorities for the period 2006 to 2010. These analyses looked at crashes by crash location and casualties based on residency, broken down into themed measures for at-risk groups. The intention was to provide instant answers for local authorities wishing to judge their own performance against national baselines on a number of important measures.
In 2012 this analysis was not only updated to include 2011 data but also substantially improved to make it even more relevant and easier to interpret. The most significant difference was the introduction of an improvement index which measured change between the first three years (2006 – 2008) and the most recent three years (2009 – 2011). These improvement indices are available for all measures where significant numbers of crashes and casualties are available at local level. Measures where numbers are relatively small are only shown as national indices, for example in the case of pedal cyclists.
In 2013, there has been a further update to include 2012 data, so the 6 year range is now from 2007 to 2012 and the improvement index is now calculated based on data from the periods 2007-2009 and 2010-2012. Road Safety Analysis has now produced 51 thematic maps which allow MAST users to compare baseline data easily across a number of key indicators for local authorities. This article explains how they were calculated and what the maps show.
All these maps are based on 6 years of STATS19 data, from 2007 to 2012, provided by the Department for Transport for MAST Online. Casualty maps are shown at local authority district level and crash maps are shown at highway authority level. Casualties are expressed relative to population size, while crash maps are expressed relative to an appropriate traffic flow or road length measure. All indicators are shown as indices where an index of 100 represents the national norm. For maps showing overall rates for the whole period, higher index values denote higher risk. For maps showing progress between two three year periods, higher index values denote less progress.
The maps are stored on 3 different layers: casualties by residency and local authority district; KSI casualties by residency and local authority district; and crashes by crash location and highway authority. Casualty maps are shown in blue and crash maps are shown in orange.
On all the maps, darker colours denote higher risk or less progress.
In order to get the most out of these maps, we have produced a guide to using eSpatial.
What the maps show and how they were calculated
Casualties by residency
This set of indicators is, we believe, the most interesting and useful. Instead of measuring stretches of tarmac, we have mapped the home postcodes of casualties in order to show areas of particularly high or low resident risk using indices. Casualties are examined on the basis of where they live rather than where they crashed because residency is the most appropriate basis for measuring socio-demographic factors which influence road risk. Since about 2 out of 5 crash victims are injured outside the district where they live, it is inadvisable to equate “crashes on local roads” with “risk to local population”.
In order to produce residency indicators as accurately as possible, the issue of unknown postcodes has to be addressed. Postcodes are not always recorded and some areas have better reporting practices than others. If all unknown postcodes were removed from the analysis then areas with low reporting rates are likely to have low resident risk (because a large percentage of these casualties are likely to have been local and would not have been counted). We have therefore created ‘correction factors’ to allocate all unknown postcodes to an authority area. This is done on the basis of the percentage of casualties reported by each police force who live in each authority area. Unknown postcodes were redistributed to authority areas based on these percentages, on the assumption that casualties with unknown postcodes are likely to be similarly distributed across authorities as known residency casualties.
There have been significant changes in road risk over recent years, and previously there has been no straightforward way to explore varying performance around the country. Using the same six years of data employed in calculating the national risk indices, it is possible to measure change in relative performance between the first and second three year periods. The analysis does not take into consideration any change in population between the periods. The rate of change in resident casualties between these periods has been calculated and indexed to demonstrate local change relative to the national picture. It should be noted that although an index value of over 100 represents less improvement than the national trend, this does not necessarily mean that resident casualties have increased in absolute terms.
KSI casualties by residency
This layer focuses only on killed and seriously injured casualties. It has similar thematic maps to the casualties by residency layer but only shows KSI casualties for the various road user groups. Because sample sizes are smaller, there is more local variation than is the case for analyses covering all casualties. This is particularly true for smaller road user groups.
Crashes by location
The purpose of this indicator is to show the risk of a vehicle being involved in an injury crash on the road network of a specific highway authority area. This measure of incidents is expressed as a rate per authority and as an index comparing local performance with the national norm. This norm is equivalent to a value of 100, with lower index values representing lower risk compared to the national average and vice versa for higher risk indices. For example, an authority with a rating of 95 has a 5% lower risk of vehicles becoming involved in an injury crash than the national average. As with the resident casualty indicator, recent progress thematic charts are also present, to show performance in the past 3 years (2010-2012) compared to the previous 3 years (2007-2009).
Using the Maps
We hope that these maps will provide a starting point for setting local road safety priorities by putting local performance meaningfully into a national context. They should allow local road safety professionals and decision-makers to determine the extent of their casualty and crash issues compared with other authorities and to choose how to distribute limited resources between road user groups based on risk at both local and regional level.