This document provides further information on the methodology used to quantify the impact of temperature and rainfall on the number of road casualties in order to produce a weather-adjusted road casualty series. Weather patterns have been used to help explain year-on-year and quarterly changes in road casualty numbers in recent publications (see https://www.gov.uk/government/collections/road-accidents-and-safety-sta…). For the Reported Road Casualties Great Britain: 2013 Annual Report a chapter was included to summarise the literature available on weather impacts on road accidents and casualties as well as discussing the main weather trends seen since 2010 and their likely impact on road casualties (see https://www.gov.uk/government/statistics/reported-road-casualties-great…). This article sets out the methodology that has been used to quantify the impact of temperature and rainfall on the number of road casualties in order to produce a weather-adjusted road casualty series. The Department for Transport volunteered to be part of a cross government group looking at how the weather impacts on different types of statistical series could be assessed. As part of this work a guide to modelling the impact of weather and climate on official statistics has been produced by the ONS Time Series Analysis Branch (see https://www.civilservice.gov.uk/wp-content/uploads/2015/04/Exploring-th…). As part of this modelling guide a case study on the impact of temperature on the monthly number of killed or seriously injured vulnerable road users (pedestrians, pedal cyclists and motorcyclists) was undertaken. Detailed results of this work can be found on page 74 of the modelling guide and are summarised in the section below. (Author/publisher)
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