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:

• Side marker lamps annually prevent 106,000 accidents, 93,000 nonfatal injuries and $347 million in property damage.

• The lamps have not been effective In reducing fatalities

• They add $21 (in 1982 dollars) to the lifetime cost of owning and operating motor vehicle.

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:

• Identical results were obtained from North Carolina and Texas.

• Two virtually independent analysis techniques were used on each file. One was straightforward (simple comparison of model years 1967 when most vehicles did not have the lamps and 1968 when most did) and the other complex (regression): they produced the same effectiveness estimate.

• Several techniques were used to check for biases in the effectiveness estimates. They suggested that the estimates were unbiased.

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:

Effectiveness of side marker lamps

• If none of the cars, trucks and buses operating on the roads during 1980 had been equipped with side marker lamps there would have been 661,000 police-reported nighttime angle collisions. If all of those cars, trucks and buses had been equipped with side marker lamps, there would only have been 555,000 collisions. In other words, the lamps reduce the number of nighttime angle collisions by 16 percent. The accident reduction is statistically significant (confidence bounds: 10 to 22 percent).

• Side marker lamps reduce the number of personal injuries in nighttime angle collisions by 21 percent. The reduction is statistically significant (confidence bounds: 12 to 29 percent).

• The statistical analyses of fatal angle collisions did not indicate a significant effect for side marker lamps (confidence bounds for effectiveness: -25 to +13 percent). An analysis of crash speeds,

• Sighting and stopping distances suggested that the effectiveness of side marker lamps in fatal crashes, if any, is at most 1/4 as high as in nonfatal crashes: at the traveling speeds prevalent in most fatal crashes, either the lamps are seen too late for drivers to react to them and stop or slow down or the headlamps are more readily visible than the side marker lamps.

Cost

• The costs per vehicle (in 1982 dollars) for side marker lamps are the following:

  Initial purchase price increase	$16.76
  Lifetime fuel consumption due to 2 pound weight increase	2.00
  Lifetime fuel consumption: electric power to light the lamps	2.19
  Lifetime cost of replacement bulbs	0.27
  TOTAL COST PER VEHICLE	$21.22

• The annual cost of side marker lamps in the United States (based on 12.3 million cars, trucks and buses sold) is $261 million.

Annual benefits

• The annual benefits, when all cars, trucks and buses in the United States have side marker lamps, will be:

  Reduction of	Best Estimate	Confidence Bounds
  Police-reported accidents	106,000	65,000 - 149,000
  Nonfatal injuries	93,000	51,000 - 132,000
  Property damage	$347M	$213 - 488M

Cost-effectiveness

• Since side marker lamps save 93,000 injuries and cost $261 million, they eliminate 360 injuries per million dollars of cost (confidence bounds: 200 to 500).

• Since side marker lamps save $347 million in property damages and cost $261 million, they save consumers $86 million per year (confidence bounds: -48 to +227 million dollars saved per year).

• Side marker lamps have significantly reduced the number of nighttime angle collisions that occur in the United States.

• The lamps have significantly reduced the number of nonfatal injuries that occur in nighttime angle collisions, because they reduce the severity of accidents and/or prevent them entirely.

• The lamps have little or no effect on fatalities. Most fatal nighttime angle collisions involve one of the vehicles traveling at high speed or both vehicles traveling at similar speeds. In the first case, by the time that the high-speed driver sees the other vehicle's side markers, there is no longer room to stop or substantially slow down; in the second case, each driver can see the other vehicle's headlamps more easily than the side marker lamps.

• Side marker lamps are a cost-effective safety device.