Traffic in Great Britain - quarterly bulletin

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Seasonal adjustment

  • Road traffic, like many other time series, exhibits seasonal variation. During the summer, for example, motor and pedal cycle traffic normally rises, due to the better weather with the converse occurring in winter.
  • The aim of seasonal adjustment is to identify and remove known seasonal effects from a time series. Where the seasonal effects are regular and relatively large in comparison to other factors, they can be identified with some confidence. Consequently, their removal will significantly improve the usefulness of the data and aid interpretation.
  • The data in Tables 1 and 3 are therefore presented on a seasonally adjusted basis. This enables easier interpretation of underlying trends, especially changes between successive quarters.