Underride Revisited


Revisited Again By Joseph E. Badger
[What follows is the final draft of a manuscript accepted and published by Law & Order magazine in August 1992. Reprinted with permission of the author. Minor changes have been made for this electronic entry.]

Prior to my retirement from active law enforcement (November 1988), I reconstructed an inordinate number of side “trailer underride” accidents. This prompted my first article on the subject, “Trailer Underride: The Almost Always Fatal Collision,” (Law & Order, May, 1988). For those of you who missed it, the side trailer underride phenomenon to which I refer is the type of nighttime accident where a tractor-semitrailer stops on a roadway and the driver begins a backing maneuver into a driveway or loading dock area. It can also happen when the driver pulls the rig out onto the highway from a loading zone or driveway, but this occurs less often.

Oncoming motorists, unaware that the trailer is across the road, see the headlights of the tractor and merely assume the lights are on a truck in its proper lane. Of the three typical trailer side marker lamps, one is blocked from view by the tractor and the other is off the roadway into the driveway. That leaves only the center marker lamp visible to the motorist. As the amber light is quite small, it may be mistaken for a roadside reflector, the type used on mailboxes, utility poles and as driveway delineators. Although it can be seen, the motorist does not perceive it as a hazard until it is too late.

Since I wrote the 1988 article, I have become involved with the reconstruction of numerous other types of underride cases where conspicuity is a problem. Certainly, we have all been called to accidents where someone runs into the rear of a semitrailer on the open highway. Everyone testifies that the taillights on the trailer were on which begs the question: “Why did the motorist run into the back of the trailer?”

Part of the problem is driver expectation. What can a reasonable and prudent person expect when driving at night? If on an interstate, most of the large trucks run “in the vicinity” of the speed limit. Car drivers expect that. If, however, a semi has pulled directly onto the roadway from the emergency lane or for some reason is traveling, only 30 MPH, a motorist may see the taillights and clearance lights but gains on the truck faster than expected. By the time the driver realizes the truck is going much slower than normal, he or she may be too close to avoid it.

In its publication “Conspicuous Problems…Conspicuous Solutions,” 3M defines conspicuity as “The degree of observability of an object. The ease by which an object can be perceived. Drivers recognize objects by five visual cues of conspicuity: Detection, Estimate of Distance, Determination of Length, Assessment of Shape, and Definition of Object’s Relative Position.”

There are also instances of vehicles running into the rear of tractor/trailers that are parked on the emergency strip. Since the emergency strip is clearly that, a stopping place for emergencies, a driver unfamiliar with the road may perceive the truck ahead to be merely going down the road in the driving lane. In too many cases, truckers fail to place warning devices (reflectorized triangles) behind the trailer so there is nothing to alert the motorist that something is amiss. A motorist may see the taillights and/or clearance lights on a trailer but again quoting the 3M publication: “‘Red dot confusion’, or the difficulty in interpreting lights a driver sees at night, adds to the problem. Too often, car drivers don’t see trucks until too late.”

There are also cases, usually in industrial areas, where a car on a side road comes to a cross roadway. A slow moving tractor passes by the side road and the motorist pulls out only to run into and under the unseen semitrailer.

This article deals with yet another situation that results in the hazards of trailer underride. Besides pulling out of or backing into driveways, other dangerous maneuvers often end in tragedy. One such is a tractor/trailer making a UTurn at a crossover on a 4lane, divided highway (or any UTurn in a rural, unlit area).

These nighttime accidents generally take place in an area where ambient light is almost nonexistent. The tractor/trailer is going one direction and at some point in time the driver realizes it is the wrong direction. Rather than continue ahead to find a more suitable place to turn around, the driver attempts to make a UTurn at a crossover, intersection, or in the middle of nowhere.

In one example the driver begins the UTurn but due to the length of the rig cannot complete the maneuver in one fell swoop. He gets halfway though the turn, stops, and jockeys back and forth until he can continue forward. Because the trailer bulkhead obscures the trucker’s vision, he is unable to see over his right shoulder toward approaching traffic. Since the roadway was clear when he first started to negotiate the turn, the driver erroneously assumes it’s still clear. However, the trucker must realize how long this exercise will take. If he stopped in the crossover, moved forward and stopped again, the procedure to this point could take 1012 seconds. A car traveling at 55 mph will travel from 808 to 970 feet in that time frame. If there are any curves, hills, trees in the median, etc., it is quite possible any traffic was out of sight when the truck’s maneuver began.

In this case, the motorist does not see any headlights of the tractor for they are pointed the other way. The sides of trailers normally have but three lamps and three reflectors. In the example, the rear markers are in the median and the front ones are off the road to the right. Only the center light and reflector are visible.

Now let’s return to driver expectation. As you drive along the only thing in your lineofsight is the single middle amber light. As you have no reason to expect an amber light ahead of you, you may SEE the light, but do not PERCEIVE it as a hazard. It could simply be a sodium vapor light off in the distance. Should there be city lights or other illumination down the road, the trailer will be but a black silhouette in the darkness.

At some point in time, the motorist may discern the trailer. If he does, it will take a while for it to “sink in.” If the driver does perceive the trailer, his mind races as to what to do about it. Since the entire roadway is blocked, swerving is out of the question and the only option left is to lock the brakes. In most cases there are no skidmarks so we never know whether the driver ever perceived the trailer and if he did, he was too close to leave any skidmarks.

In a few cases, you may find that the underriding motorist had been drinking or influenced by some other drug. Granted, drugs dull the senses, interferes with judgement which usually increases perception time. However, many such accident cases involved “normal” drivers. Quite a few have been elderly (and we must realize the nighttime acuity of vision of the chronologically gifted isn’t what it used to be) but trailer underride knows no bounds when it comes to age, mentality, sex or other differences in motorists.


The trucking industry has known about this problem for years. I have personally been involved in accident cases that have gone into litigation and the awards are often substantial. And word of multimillion dollar lawsuits spreads rapidly.

Brian O’Neill, president of the Insurance Institute for Highway Safety (IIHS), in a statement before a Select Committee in the U.S. House of Representatives, addressed the issue of tractor/trailer conspicuity in general and truck underride in particular. He was speaking mainly about rear end collisions, but in the IIHS “Status Report” (December 31, 1991) side impacts are mentioned:

“Crashes in which large truck trailers are struck in the side or rear could be reduced by 15 percent if the vehicles were more visible in the dark and in bad weather, estimates the National Highway Traffic Safety Administration (NHTSA).” The agency is proposing that manufacturers install reflective patterns on trailers to ‘help motorists judge size, shape, and distance.’

“The proposed conspicuity rule requires manufacturers to install ‘retroreflective sheeting or reflex reflectors’ on the sides and rear of trailers with a width of 80 inches or more and a weight rating of more than 10,000 pounds.”
[Note: Since this article was originally published, the proposal became effective for trailers manufactured on or after December 1, 1993.]

For those of you interested in reading more about the Federal Motor Vehicle Safety Standard (FMVSS) and to see illustrations showing how trailers should be marked, I refer you to the Department of Transportation’s 49 CFR Part 571, Docket No. 809; Notice 4; RIN 2127-AA12. It is subtitled “Lamps, Reflective Devices, and Associated Equipment.” Contact NHTSA’s Docket Section, Room 5109, NASSIF Bldg., 400 7th St., S.W., Washington, D.C. 20590; (202) 366-6346.

As stated earlier, the problem has been known in the trucking community for some time. Quoting the Federal Register, Vol. 56, No. 233, “On May 27, 1980, the agency [NHTSA] issued [a request] for comments on methods to reduce such collisions by improving the conspicuity of large commercial vehicles that could lead to the issuance of a proposal. Forty two comments were received, most of which favored the concept.”

All of this rulemaking seems to be aimed at manufacturers. But what of the millions of tractor/trailer combinations already on the road? A number of firms, such as Avery, Reflexit, and most notably 3M, have developed aftermarket products to enhance the conspicuity of semi trailers.

A spokesperson with 3M’s Commercial Graphics Division advised me that they have developed Scotchlite(tm) Diamond Grade Conspicuity Sheeting, Series 980. This adhesive tape, when applied to existing trailers, has a “minimum 600 candlepower brightness; 900 candlepower typical.” It reflects to near 90 degrees and has a seven year performance life. The tape comes in 2″, 3″ and 4″ widths and is easy to apply (designed for flat surfaces, but will apply over rivets if cut out).

This isn’t merely “shiny tape.” According to 3M’s “Product Bulletin 980”, “This highly retro-reflective sheeting consists of prismatic lenses formed in a durable transparent resin, sealed with a white synthetic film and backed with an aggressive pressure sensitive adhesive. . ..”

In February (1992), I spoke with Ron Harold, President of Tennessee Truck Lines, Inc. His company has 500 semi trailers each of which is equipped with 3M’s Scotchlite tape. He advised the 2″ tape runs about $1.20 per foot and “is almost as effective” as the 4″ tape. Mr. Harold told me that it costs about $150 to outfit one trailer which amounts to $75,000 for the entire fleet. Sounds expensive, but it is more than offset in a single lawsuit that could cost many millions of dollars.

Further, Mr. Harold and I discussed the insurance angle. When asked if his insurance rates were less because he used the tape, he said once you demonstrate decreased accident frequency [after the tape has been applied], your rates decrease accordingly.

Another trucking company representative stated that after using reflective material for eight years they had reduced accident claims and lower insurance rates to prove it.

It may sound like I’m selling 3M products. What I am selling is safety. As accident investigators and reconstructionists, you should promote safety at every opportunity. When working nighttime trailer underride accidents pay particular notice to the rear and side markings on the involved trailer. Take photographs with and without a flash attachment. How much “normal traffic” light is reflected by the trailer?

A lot of us use the typical one second for perception and three quarters of a second for reaction and then so many feet to slide to a stop. But, does this work for a nighttime driving situation when you have wet pavement and an UNEXPECTED FIXED OBJECT? A driver may see and eventually perceive a trailer in front of him, but it’s going to take a lot longer before he realizes IT ISN’T MOVING! One “decision sight distance time model” indicates that at 30 MPH it takes 10.5 seconds and 460 feet from the time an “unexpected fixed object” becomes visible for the driver to “see” it, recognize hazard, decide on action, initiate action, and complete maneuver. At 60 MPH, the distance could be 1275 feet. This of course does not involve hitting the brakes, but in steering around the hazard.

At least on the open road, drivers expect to come up behind the back of semitrailers sooner or later. However, they would not reasonably expect to find an object the size of a small house crosswise in the road ahead.

As accident investigators, keep in mind the safety standard. Quite often, officers fault a driver who, from all outward appearances, simply runs into the back or side of a stationary (or nearly stationary) vehicle. After all, the investigation indicates the struck vehicle had the DOT required lamps and reflectors. Even if the trailer doesn’t come under the FMVSS rule, the industry is aware not only of the proposed legislation but of the problem of trailer conspicuity.

In a rear underride case, note first whether the trailer had a properly installed DOT bumper (when required). If not, you can cite the trucker as well as his company. Secondly, note if the bumper conforms to code (many do not extend far enough toward the sides of the trailer). Third, did the bumper collapse (it’s supposed to be “substantial)?

Besides installing reflective materials to the trailers, trucking companies should school its drivers regarding the potentially dangerous practice of backing across roadways and making UTurns at night. Every driver should be aware of the capabilities of the truck, its total length, its acceleration capacity, the amount of time it will take to make particular maneuvers, etc.

Many trucking firms offer their drivers no training whatsoever. Management often responds by saying they hired a supposedly “professional driver” who should know all the rules. However, it is incumbent on the company to ascertain the level of proficiency and knowledge a particular driver has of the equipment he or she will be operating.

Granted, it may ultimately be up to a jury to decide proximate cause or percentage of fault; however, you as the initial investigator can assist the trier of fact if you have done not just a report but a thorough investigation.


Joseph E. Badger, retired Indiana state police sergeant, is a nationally known, ACTAR accredited expert in the field of accident reconstruction and a frequent contributor to LAW and ORDER. He may be reached via email at jebadger1@comcast.net.


The author wishes to thank the following for their cooperation and assistance: Marie Niernberger, Audiovisual Specialist, Insurance Institute for Highway Safety, who provided valuable material; 3M’s Commercial Graphics Division, for research literature and information; Ron Harold, President of Tennessee Truck Lines; and James Harris, Harris Technical Services, for plotting my computer prepared diagrams for the original publication.

Joseph E. Badger

For further reading:
You can order Joseph Badger’s fully illustrated 36page, spiralbound book:
Trailer Underride: Conspicuity, Human Factors and Rear Bumper Revised edition now available

Write to:
University of North Florida
4567 St. Johns Bluff Road, S.
Jacksonville, FL 322242645

Cost is $24.95 plus $4.00 s&h