External-To-Vehicle Driver Distraction (Research Findings No. 168/2003)

  • Published: Human factors Analysts Ltd, for the Scottish Executive, 2003
  • Authors: B. Wallace
  • Date Added: 07 Feb 2013
  • Last Update: 07 Feb 2013
  • Format: pdf


The Scottish Executive commissioned a literature review on driver distraction to explore in more depth whether external driver distraction is a significant factor in road RTIs and to examine existing knowledge and gaps on the relevant external factors that cause vehicle RTIs, with a view to identifying where further research might be carried out.


The research was carried out by Human Factors Analysts Ltd. (HFAL) a ‘spin-out’ company from the University of Strathclyde, between December 2002 and March 2003. It consisted of a literature review of all relevant material relating to external-to-driver distraction published since 1945 in English. However, it was necessary to also obtain literature relating to general theories of driver distraction and general studies of driver distraction, to provide a contextual background.

Key Findings:

  • Information from RTI databases suggests that external-to-vehicle driver distraction is a major contributory factor to road RTIs. However it is likely that these incidents are under-reported. The real risks may therefore be greater than official statistics suggest.

  • The evidence suggests that there are two specific situations where the risk factor of billboards and signs is at its highest: at junctions, and on long monotonous roads (such as motorways).

  • Overall the literature review found that advertising/billboards can function as distractors in specific situations. However, more research is needed to discover in what particular situations they pose most of a threat, and the precise extent of the risk.

  • The general conclusion is that between 10 per cent and 30 per cent of all RTIs have driver distraction as a contributory factor, and that, of these, roughly a third are specifically caused by external-to-vehicle driver distraction. Young (aged17-21) drivers are particularly prone to external-to-vehicle driver distraction. It is, however, thought that these figures are an underestimate.

  • External distraction is thought to be caused by one of two factors: visual ‘clutter’ (occurring mainly at junctions); and ‘low arousal’ during monotonous situations when the driver is ‘surprised’ by a billboard or sign and fixates on it after a long period of driving.

  • Most research into external driver distraction originates in the USA or Australia. It is recommended that further research is carried out in the UK.


Distraction, RTIs, safety, signs, advertising signs, clutter.


Robust government summary document. However, signs only form part of the analysis. Slightly dated.