NHTSA Report Number DOT HS 806 430July 1983

An Evaluation of Side Marker Lamps For Cars, Trucks, and Buses

Charles J. Kahane, Ph.D.


Side marker lamps were installed in cars, trucks, buses, trailers and multipurpose passenger vehicles in response to Federal Motor Vehicle Safety Standard 108. The purpose of side marker lamps is to enable a driver to see another vehicle that is approaching at an angle at night--and to see it early enough that the driver can stop in time to prevent a collision or, at least, slow down to reduce the severity of the collision. The objectives of this agency staff evaluation are to determine how many accidents, casualties and damages are prevented by side marker lamps and to measure the actual cost of the lamps. The evaluation is based on statistical analyses of North Carolina, Texas and Fatal Accident Reporting System data, a study of traveling speeds in fatal angle collisions, and cost analyses of production lamp assemblies. It was found that:


The most notable change in motor vehicle lighting during the period 1965-75 was the installation of side marker lamps on most cars, trucks and buses in 1968. Before that year, most vehicles did not have any illumination visible from the side. The purpose of side marker lamps is to enable a driver to see another vehicle that is approaching at an angle at night (or is standing still with its side facing the driver)-and to see it early enough that the driver can stop in time to prevent a nighttime angle collision or, at least, slow down or take evasive action to reduce the severity of the collision.

Federal Motor Vehicle Safety Standard 108 regulates the lamps, reflectors and associated equipment for cars, trucks, trailers, buses, multi-purpose passenger vehicles and motorcycles. It became effective on January 1, 1968, for vehicles wider than 80 inches (large trucks and buses) and on January 1, 1969, for the other vehicles.

Executive Order 12291 (February 1981) requires agencies to evaluate their existing major regulations, including any rule whose annual effect on the economy is $100 million or more. The objectives of an evaluation are to determine the actual benefits - lives saved, injuries prevented, damages avoided - and costs of safety equipment installed in production vehicles in response to a standard and to assess cost-effectiveness.

This report is an evaluation of side marker lamps for cars, trucks, vans and buses-the only significant change in the lighting systems of production vehicles that more or less coincided with the effective date of Standard 108. They were introduced voluntarily by manufacturers, typically one year before the standard's effective date. The other lighting systems of motor vehicles (headlamps, brake lights, etc.) for the most part already met Standard 108 many years in advance because they complied with SAE Standards and Recommended Practices that were incorporated, by reference, into Standard 108.

Estimates of the number of accidents and casualties prevented by side marker lamps were obtained by statistically analyzing accident data from the North Carolina and Texas State files and the Fatal Accident Reporting System. The analyses of nonfatal accidents resulted in precise, statistically significant, effectiveness estimates. The analyses of fatal crashes did not produce statistically significant estimates and were supplemented by an engineering study: did drivers in fatal crashes have enough room to stop or slow down after they saw the lamps? The cost of side marker lamps was estimated by analyzing lamp components of a representative sample of cars and by obtaining data on repair frequencies and costs.

The evaluation does not develop a detailed model which predicts side marker lamp effectiveness as a function of their intensity, size, luminance or as a function of accident parameters. That model could be useful for studying the effect of potential changes in side marker lamp requirements, but the in-depth accident and laboratory data that would be needed to develop it do not exist at this tine. Instead, the evaluation is limited to assessing the actual costs and benefits of current production lamps--whose design has remained largely unchanged during 1970-83.

The most important conclusion of this study is that side marker lamps are effective in preventing nonfatal accidents and injuries--close to 100,000 of each per year. The conclusion is based almost entirely on statistical analyses of accident data, yet can be drawn firmly because of the exceptional precision and consistency of those analyses:

The other conclusion is that side marker lamps had little or no effect on fatalities. The conclusion is based on a combination of statistical analysis and engineering judgement and it is less firm than the preceding one. The statistical analysis of fatal crashes yielded an effectiveness estimate just below zero but (because the Fatal Accident Reporting System is a smaller file than North Carolina or Texas) with relatively wider confidence bounds Including a range of positive and negative values. The engineering analysis did not yield a specific estimate but did suggest that the effect, if any, was a fraction of the one in nonfatal crashes. The conclusion that the actual effect is essentially zero is conservative and consistent with both analyses.

The principal findings and conclusions of the study are the following:

Principal Findings

Effectiveness of side marker lamps


Annual benefits



Return to Regulatory Evaluation Page