Project: Effectiveness of Daytime Running Lights

Reference: S271G/VD

Last update: 03/12/2003 09:57:23


Conduct a critical review of the SWOV report with a view to giving the Department guidance on:

* the validity of the conclusions from this report;
* the need for further analysis of the existing data; and,
* the need for further research.


The use of Daytime Running Lamps (DRL's) is claimed to reduce the number of road accidents, particularly those associated with certain manoeuvres.

A number of countries have introduced requirements for vehicles to use DRL's or dipped beam headlamps during the daytime. Analysis of the consequential accident reduction would appear to suggest that the use of such lamps during the daytime is beneficial, but that the benefit increases with an increase in latitude. However, in certain cases, re-examination of the original data would suggest that the benefits may have been significantly exaggerated. Although benefits have been demonstrated, the reasons have not necessarily been fully explained, nor have the potential costs been calculated.

On the basis of the 'demonstrated' benefits, proposals are being put forward for the mandatory fitment of DRL's. However, most of the benefits have been calculated on the basis of dipped-beam headlamps being used, and these lamps have different attributes to the DRL's. These different attributes might affect the potential benefits and costs of such lamps.

Towards the end of 1997, SWOV published a report entitled "The Safety Effects of Daytime Running Lamps". The report was funded by the EC and sought to establish the benefits of DRL's. The purpose of this project is to conduct a detailed review of the SWOV report.


TRL Limited
Crowthorne House, Nine Mile Ride, Wokingham, Berkshire, RG40 3GA
+44 (0)1344 773131

Contract details

Cost to the Department: £5,000.00

Actual start date: 03 February 1998

Actual completion date: 30 April 1998


PR/SE/401/98. Review of SWOV Report on Effectiveness of Daytime Running Lights
Author: TRL Ltd
Publication date: 30/04/1998
Source: Contact:

R-97-36. The Safety Effects of Daytime Running Lights
Author: SWOV Institute for Road Safety Research. The Netherlands.
Publication date: 30/06/1997
Source: SWOV Institute for Road Safety Research. The Netherlands.

Summary of results

  1. It is very difficult to form a balanced judgement on the reliability of the claims made by the SWOV report for the effectiveness of Daytime Running Lights (DRL). In terms of methodology and scrupulous examination of the evidence, it is a most impressive piece of work. On the other hand, the report is poorly presented and the claims made for the potential accident savings appear exaggerated.

    One strong argument in favour of the conclusion that use of DRL does reduce accident risk is the fact that 24 independent studies have reached this conclusion. Estimation errors could be expected in a single study, but these should tend to cancel out when 24 studies are combined. What virtually all of these studies have in common is the use of the odds ratio (in one form or another) to estimate the effects of DRL. Some concerns were raised about this ratio, but they seemed relatively minor. The recent Hungarian evidence showed that they could be real, although the consequences for the estimation of the effect were small - perhaps by chance.

    When faced with an apparently exaggerated conclusion from the use of the odds ratio, however, the possibility that the concerns are actually more significant must be considered.