CR 218: Review of the literature on daytime running lights (DRL) (2003)

1.1 Background

Overseas evaluations have concluded that automatic daytime running lights (DRL) are effective in reducing multiple-party crashes, but many of these studies have been criticised on methodological grounds. Nonetheless, the substantial body of evidence suggesting that there are safety benefits associated with the use of DRL has prompted various proposals for Australia to adopt some form of broad-based DRL requirement, typically by amendment to design rules for new vehicles.

As input to the Department of Transport and Regional Services' examination of DRL, the Australian Transport Safety Bureau (ATSB) has commissioned ARRB Transport Research Ltd to conduct a comprehensive review and analysis of the research literature on DRL.

1.2 Principles

Failure to see another vehicle has been shown by many studies to contribute to a considerable proportion of collisions (Cairney, 1991). DRL are designed to increase the contrast between the brightness of the DRL equipped vehicle and brightness of the vehicle's background. By increasing the visual contrast of a vehicle DRL should, theoretically, allow other road users to see a vehicle more readily than would otherwise be the case, allowing them to respond to the presence of the vehicle sooner in order to avoid a collision.

1.3 Objectives

This project has three primary objectives:

  1. To identify and critically review evaluation studies and other relevant research on the impacts of DRL.
  2. To discuss the findings in relation to proposals for an Australian DRL requirement.
  3. To identify additional research or information required to fully assess the impacts of an Australian DRL requirement.

1.4 Method

In order to identify available evaluation studies and other relevant research on the impacts of DRL, several databases and the internet were utilised. Local, interstate and overseas contacts were consulted in an effort to identify any relevant unpublished material.

Three main bodies of literature were considered:

  1. 1. Experimental studies of the conspicuity of DRL in relation to ambient lighting conditions.
  2. Studies of crash reductions following the introduction of DRL in other jurisdictions.
  3. Literature pertaining to the costs of providing DRL.

Consultations with Australian jurisdictions in relation to unpublished research were extended to the views each contact had on DRL.

1.5 Impact of DRL on visibility

Studies have been conducted on the effects of DRL on visibility distance, speed and gap acceptance, vehicle detection and recognition, and discomfort glare. These studies suggest that DRL increase the probability that a vehicle will be detected when ambient lighting levels are low. They also show that if the DRL are too bright, then discomfort glare and disability glare will result. DRL should be bright enough to ensure performance is better than without DRL, but not so bright as to cause glare.

Only luminous intensities lying within a very narrow range would satisfy this condition. It might be beneficial to have DRL which are capable of varying intensities that alter in response to ambient illumination level.

1.6 Crash reduction studies: cars

Early research has provided a mix of results. Comprehensive reviews incorporating meta-analysis by Elvik (1996) and Koornstra et al. (1979) have systematised these results. Elvik showed that studies of DRL in vehicle fleets provided larger and more consistent effects than studies of traffic systems, and that outcomes are sensitive to the type of measures used. Koornstra et al. carried this analysis a step further by statistically excluding factors such as number of vehicles already using DRL at the start of a trial to estimate the intrinsic effects of DRL, ie the effects which would occur when use rate is increased from zero to 100% of vehicles. The effect of this re-analysis was to make many studies which were previously non-significant significant, and show that by far the majority of studies found a reduction in multiple-party daytime crashes associated with DRL. Koornstra et al. proposed a set of relationships relating the extent of crash reductions with DRL to latitude, based on the longer hours of twilight in the higher latitudes. It should be noted that many later studies do not fit this model well.

Studies that have been conducted since the reports of Elvik (1996) and Koorsntra et al. (1997) have generally confirmed the reduction in crash rates associated with DRL, although the size of the reduction varies. Tofflemire and Whitehead (1997) compared crash rates in the same year for Canadian cars with and without DRL, eliminating factors such as weather, economic climate, and enforcement as a possible source of differences. They found an overall reduction of 5.3%, principally due to a reduction in crashes involving vehicles travelling in opposite directions.

A North America study by the National Highway Traffic Safety Administration (NHTSA, 2000) reinforced the sensitivity of outcomes to analysis methods, but showed an estimated effect of DRL was a reduction of 7% in multiple-party daytime crashes, which was statistically significant. Bergkvist (2001) reports upon a study conducted for General Motors Corporation by an independent consulting firm. The study involved a comparison of the crash rates of specific GM, Volvo, Saab and Volkswagen vehicles before and immediately after DRL became standard equipment on these models. The results suggest a reduction in the incidence of target vehicle-vehicle crashes in excess of 5% and a reduction in vehicle-pedestrian collisions of approximately 9%. Farmer and Williams (2002) compared makes and models which included DRL as a standard feature with the same makes and models purchased before this was the case. The reduction in daytime crashes was 3.2%, which was highly significant. When considered separately, all states but one showed a reduction in crashes for the DRL vehicles. However, only in Texas was the reduction large enough to be statistically significant. Lassarre (2002) reports a trial involving a campaign to encourage voluntary use of headlights during the day. Crash rates in the area where the campaign was run were compared with crash rates in neighbouring areas over the same period, and showed a reduction of 58.7% for fatal crashes and for serious injury crashes on major roads, but no reductions in less serious crashes and no effects on crashes on minor roads.

A study by Poole (1999) is of particular interest as it is the only fleet study carried out in Australia. DRL were fitted to 80 fleet vehicles based in metropolitan Western Australia. The crash records of the DRL equipped vehicles over a ten month period were compared with the crash records of a matched sample of vehicles not fitted with DRL. Results based on a time-to-crash analysis found that DRL fitted vehicles took more than five times longer than non-DRL fitted vehicles to be involved in a vehicle-vehicle daytime crash.

1.7 Crash reduction studies: motorcycles

There are reasons for believing that the case for DRL as a countermeasure for motorcycle crashes is even more compelling than that for cars, as cars are more conspicuous than motorcycles. Laboratory studies and field trials have demonstrated that motorcycles equipped with DRL are more easily seen than motorcycles without such equipment.

1.7.1 Studies of causal factors in motorcycle crashes

Studies of causal factors in motorcycle crashes have revealed that crash-involved motorcyclists are less likely to be using DRL at the time of the crash than non-crash involved motorcyclists.

A Californian study on the effects of a law requiring that new motorcycles have DRL fitted revealed no effect on fatalities and a non-significant reduction in vehicle-vehicle daytime crashes. Two studies of the effect of the Australian Design Rule (ADR 19/01) requiring hard-wired DRL on new motorcycles in Australia have been carried out, both finding small but non-significant reductions in crashes. The number of crashes on which these studies were based was too small to conclude that DRL are ineffective.

Two studies from Malaysia and Singapore provide some positive evidence in relation to daytime use of headlights for motorcycles. A national campaign to increase daytime headlight use in Malaysia resulted in an 82% headlight use rate and a reduction in conspicuity-related crashes of 29%. Compulsory headlight use for motorcyclists in Singapore was found to result in a significant reduction in fatal and serious injury crashes.

1.8 Consultations with Australian jurisdictions

Representatives of the traffic authority of each Australian State and Territory were contacted by telephone and asked to comment on each of three DRL options. Representatives from most jurisdictions could offer only personal opinions, but most were in favour of the introduction of DRL in some form. The most favoured of the three options presented is the introduction of an ADR requiring all new vehicles sold in Australia to be fitted with a device that automatically activates either the vehicle’s headlights or separate running lights, when the engine is operating. No representatives expressed support for the introduction of State and Territory laws requiring that drivers of all vehicles activate headlights, or separate running lights, at all times of vehicle operation.

1.9 Benefit-cost estimates

Two recent studies of DRL are of particular interest. A New Zealand study considered the costs and benefits of DRL with normal headlight use and with retrofitted DRL. Koornstra et al.’s formulae were used to estimate crash reductions. Special purpose DRL were found not to be cost-effective, while use of normal headlights as DRL was found to be cost effective only when petrol prices were low.

A study carried out for the NRMA and RACV (Paine, 2003) examined technical options for DRL in some detail, and estimated crash savings based on the NSW crash database, using Koornstra’s formulae to provide an upper estimate and Berkvist’s results as a lower estimate. With the lower estimate, only factory fitted special purpose DRL were found to be cost effective. With higher estimates of crash savings, several options were shown to be cost-effective.

The present study adopted a generally similar approach, based on the VicRoads CrashStats database and Koornstra’s formulae. The option of using normal headlights had a benefit-cost ratio of just over 1.0. Costs were greatly reduced by having dedicated DRL which consumed less power. Costs were further reduced by having sensor-activated DRL which only come on in periods of low ambient illumination; in providing a benefit-cost estimate for this option, it was assumed that all crash reductions would be concentrated in these periods, but this assumption is unlikely to be true in practice. Although visibility tests suggest that DRL are effective only in low-light conditions, there do not appear to be any studies that indicate what proportion of DRL-related crash reductions actually occur during such periods.

Differences between these benefit-cost estimates are discussed in detail.

1.10 Unresolved issues

The main issues yet to be resolved are:

  • A closer examination of the data on crash reductions in different circumstances to be able to better predict what the effects in Australia might be, although it is unlikely that exact prediction of outcomes in Australia will be possible.
  • A closer examination of the costs of providing DRL.
  • Consideration of likely road user acceptance.
  • The need for arrangements to manage the transition as new DRL equipped vehicles appear on the roads.

1.11 Conclusions

  1. There is a substantial body of evidence which shows that DRL reduce daytime crashes. However, there is considerable variation in the size of the reduction reported in different studies.
  2. Most studies simply report overall reductions. As a result, three issues remain unresolved, or have little data to support them. Resolution of these issues would clarify the likely effects of DRL in crashes in Australia, or would help decide between having full-time DRL and DRL which operate only under conditions of low illumination. They are:
    • What is the relative effect in built-up areas and open country?
    • How much of the crash savings occurred during the dawn/dusk period, and how much during conditions of low ambient lighting?
    • How have different crash types (cross traffic, right (or left) turn against, head-on, etc) been affected?
  3. Empirical work has shown which type of DRL is most suitable. Dipped headlights, even with reduced light output, are not a good choice as much of the light is directed towards the road surface, which is ineffective during daytime (although effective at night). The best option appears to be dedicated DRL with an intensity of 1200 candelas. Although the introduction of an ADR is associated with long lead times, compulsory usage laws have little State support and are associated with compliance and enforcement problems.
  4. Opinion in the different jurisdictions around the nation indicates majority support for DRL, although it should be borne in mind that this represents the views of individual officials and not, at this stage, departmental policy. Some of the respondents contacted suggested that a clearer indication of the likely benefits in Australia would be required before full support would be forthcoming. Most favoured a national approach, and some were conscious of the benefits of aligning practice with that in the larger motor vehicle markets. A majority indicated a preference for full-time operation of DRL.
  5. The benefit-cost analysis suggested the costs of providing DRL would be considerably reduced if the DRL operated only in conditions of low ambient lighting. However, it is not possible to estimate the extent by which the crash reductions might be reduced under this option (refer Conclusion 2). In view of the jurisdictions’ preference for full-time operation, evidence in support of this option would have to be persuasive before it was adopted.
  6. An appropriate course of action for Australia will be to await the outcome of the determinations currently taking place in Europe in relation to DRL, and which are expected to be complete by the end of the year. At that stage it would be appropriate to give the issue full consideration in the light of the European decision, and the outcomes of Paine’s and the present analysis.


Type: Research and Analysis Report

Sub Type: Consultant Report

Author(s): Cairney P, Styles T

ISBN: 0 642 25510 5

ISSN: 1445 4467

Topics: Economic, Vehicle design, Visual

Publication Date: 01/01/03