Page last updated at 14:31 GMT, Wednesday, 16 December 2009

Crash: About the road fatality data

Where did the data come from?

The data for the interactive map was provided by the Department of Transport. It covers the years 1999 to 2008, the last year for when complete data is available.

Drawn from the official statistics, the data is gathered by the police at the scene of every serious road crash.

Why not show injuries as well as fatalities?

The data is very detailed, recording for example, everything from time and place, weather, road type, number of casualties and so on.

For any year the total set of crash data is huge. There are tens of thousands of reported crashes every year, with more than 250,000 serious and light injuries recorded.

It seemed sensible to concentrate on a more manageable set of data, hence the decision to limit it to fatal crashes.

Another reason for choosing this set was its accuracy.

Officials say they feel confident that every fatal road crash is recorded. The same cannot be said for serious injuries however. One survey suggested these might be as high as 800,000 per year, rather than the officially reported quarter of a million.

Is the data accurate?

The information published is official data provided to the BBC by the Department of Transport. This is not to say that there are no omissions, nor errors in some elements of that data. We have no way of checking the accuracy of the data provided, though we will endeavour to correct any that come to light.

I know of a fatal crash but it's not on the map

Where incidents are close together, they will not show up at some zoom levels. You may need to zoom in further to the map to reveal more detail.

Why is Northern Ireland not included?

The data released by the department was for Great Britain. Northern Ireland collects and releases its data separately. Trying to put the two sets of data together presented some difficulties we are looking to overcome.

Why is the data displayed by police authority?

Since the statistics are recorded by each police authority areas, we decided to use this as a basis for loading up small chunks of the data at any one time. This should make it quicker to load for most computers

So, when you choose a police area or type in your full post code, it should load the crashes for that area. There are some anomalies however. Not all postcodes will lead you to your county police authority. The Metropolitan police area, for example, includes parts of several counties.

If you follow a road, the M1 for example, along its length, the map will automatically load new crash locations as fresh sections of the map are loaded.

Undoubtedly, this is a partial view of the road crash statistics.

It doesn't, for example, show you the level of traffic on a particular road at the time of a crash. It doesn't include detail of the contributing factors either. There are news reports with some of the locations, that give further detail released by the police at the time, or later at an inquest or court case.

You can however, dissect the total data by category in our interactive graphic . This splits out fatal road crashes according to gender, mode of transport, weather, and so on.

We will continue to monitor the use of the information contained in the map and graphics and aim to improve it as time goes on.

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