Nighttime Tractor Trailer Side Underrides
(The Invisible Semi)

By: Robert L. Parke, CLI

Parkediagrm.jpg (9006 bytes)
Figure 1
Graphic courtesy of
Benedict Engineering Company, Inc. Tallehassee, Fl.

In 1967, near New Orleans, actress Jayne Mansfield received fatal injuries when her automobile struck the rear of a semi tractor, underrode it, causing her virtual decapitation. The remarkable aspect of that crash is that it happened over thirty years ago and received much publicity, yet very little has been accomplished in the ensuing years to prevent similar accidents. Not until January, 1995 did the National Highway Traffic Safety Administration (NHTSA) issue a standard that new truck and semi-trailers be equipped with a rear guard that will prevent vehicles following from underriding in a rear-end collision1. Until that time, a 1953 rule, Federal Motor Carrier Regulation 393.86, remained in effect2. The rule provided only that these guards be "substantially constructed and firmly attached." There were no guidelines for this "standard", nor were there any test requirements to prove their effectiveness. Ms. Mansfield's death in fact demonstrated their ineffectiveness. Still, it took over forty years to upgrade the standard.

In 1993, NHTSA required all new heavy and semi-trailers to be equipped with reflective tape along the rear perimeter and sides3. No requirement for retrofitting was made by NHTSA, despite numerous studies demonstrating the effectiveness of that feature in diminishing underride accidents (16 percent in daytime crashes and more than 21 percent in nighttime underrides)4. Several trucking companies' studies demonstrated the same5. Retrofit rear crash guards are available, as are side underride guards. Very few of the trucking companies are making the investment in those guards, although retrofitted reflectorized tape is becoming more and more common as the motor carriers recognize the resulting dollar savings in lawsuit damages and insurance premiums.

Jack Murray, CLI, has presented an excellent overview of the underride problem in his February 1998 article in The Legal Investigator, "Tractor Trailer Underride Accidents--Not Your Average Everyday Occurrence." He discusses many of the details of reflective tape and its efficacy, and concentrates on the rear underride problem. My discussion will focus on only one of the common types of underride accidents - the nighttime side underride.

Although side underride accidents can occur from a semi attempting a U-turn, stopping to back into a driveway, or in any other scenario which places the trailer fully or partially crosswise in the roadway, the typical nighttime underride involves a tractor trailer pulling from a rural, unlighted side road onto a two lane highway. The semi is turning left. An automobile is coming from the semi's left side, and the semi driver misjudges the distance and/or speed of the car. In some cases, it may be that the semi driver is chemically impaired, sleep-deprived, or suffers from a condition we can call "driver arrogance" (as in, "I'm bigger than you, so you'd better not hit me.") That attitude usually works in the daytime, and most of us have had the experience of having to slow or even stop to allow a semi trailer to clear our lane. At night, it often doesn't work that way. The car hits the side of the trailer, and the result is death or catastrophic injury to the occupants of the car.

Conspicuity is a fancy word used to describe how well something can or cannot be seen under existing conditions. It simply means, is it or is it not conspicuous, and to what degree? Jack has discussed the use of reflectorized tape on the rear and sides of trailers, and the relatively low cost of retrofitting trailers (between $75 and $150, depending on whose figures you read) with reflectorized tape strips. That's not much to save a life, but incredibly, there are still thousands of tractor-trailers in operation on our highways that do not have this safety feature added. For flatbed trailers, there are now available, but seldom used, reflectorized tarpaulins. As Jack also has noted, these markings were not required for trailers manufactured prior to December 1, 1993. Unfortunately, the reflectorized strips alone may not have much effect on the prevention of some nighttime underrides.

When that semi begins making its left turn onto the two lane road from the side street, it reaches a point where its headlights are shining directly straight ahead in the lane now completely occupied by the semi tractor. The 45 foot or longer trailer is now tracking at an angle to the tractor, and still occupies some or the entire lane in which the car is traveling. With or without reflectorized strips on the trailer, now all the car driver may see is head-lights. (Figure1) There are three amber side marker lamps and reflectors required on the trailer6, but the driver of the car doesn't see them. There are several reasons why not.

When a bright light (oncoming headlights) reaches the human eye, the iris closes down to keep out some of that light. The retina of the eye contains two types of photoreceptors---rods and cones7. The rods are the important ones to this situation, because they are sensitive to dim light (the cones give color and bright light vision). The rods fatigue quickly in bright light, and must regain their sensitivity to function in the perception of dim light (as in coming into a dark movie theater from outside on a bright day). Consequently, when the oncoming light from the semi's headlamps strike the retina, the iris closes down, the rods fatigue, and peripheral lights (side marker lamps and reflectorized tape) may be physiologically impossible to perceive. Add another factor; when faced with oncoming lights, particularly if they are in the bright mode, or are angled upward from the acceleration torque of the tractor, many drivers look down and to the right--- in other words, away from the oncoming headlights. Even if the driver of the car has seen the semi's side marker or reflective strips prior to the semi beginning its turn to face the oncoming car, by the time the headlights are squarely facing the car, those clues may disappear or not be perceived as what they are. The car's driver may not realize that a portion of the semi trailer is still in the car's lane --- "The Invisible Semi-Trailer". This is partly because the corner of the tractor conceals the semitrailer's front amber light. If the rear amber light is seen at A, it may be misinterpreted as being a driveway or mailbox marker, or another kind of fixed amber reflector located off the roadway, because at this stage of the turn, the rear portion of the semi-trailer is still off the road to the car's right side. The reflectorized striping is angled away from the car's lights, reducing its reflectability. That leaves only the center amber light to be perceived by the driver of the oncoming car, and to be recognized for what it is. If the light lens or reflectorized striping is dirty, the problem is exacerbated. Recognition of a hazard may not occur.

Add one more factor: most state uniform traffic codes require a car's headlights to illuminate objects 450 feet away on high beam, but only 150 feet on low beam8. If the driver of that car has done the courteous (and legally required) thing, and dimmed the car's lights because of the now oncoming vehicle9, the headlight visibility has been reduced by 2/3. At this point, there is now a critical distance. That is the distance between the front of the car and the left rear comer of the semi trailer. If that distance is sufficient, the trailer clears the car's lane, and all is well. If not, the car impacts some portion of the side of the semi trailer. If impact between the front of the car (or pickup or sport utility vehicle) and the semi-trailer is between the rear dual tires of the tractor and the front dual tires of the trailer, a complete underride can occur, or at least, substantial penetration of the car under the trailer will result. If the car hits the rear duals of the tractor with the left front, the car will rotate right, so that the passenger side underrides the trailer. If the right front of the car hits the rear duals of the trailer, the car will usually rotate left, exposing the driver's compartment to the greatest underride penetration. If the car misses the semi-trailer' rear wheels, but hits the overhanging left rear comer of the semi-trailer, there is catastrophic intrusion into the driver's compartment through the windshield and A pillar.

Unlike a frontal collision into a barrier (or another car or pickup), underrides cause damage mostly above the solid structures of the vehicle (bumper, frame and engine). The strike is usually at or just below the leading edge of the hood, which peels backwards, the windshield may be penetrated, and then the roof may be pulled downward from A pillar deformation or shifted rearward if the A pillar shears (Photo 1). This makes for some very dramatic damage, but does not reflect the speed that would be required for similarly appearing damage in a barrier crash. It is not uncommon for the police to therefore overestimate the speed of the underriding vehicle. This factor makes it crucial to involve a reconstructionist as soon as possible. Engineers or other such skilled technicians can calculate the speed at impact with precision. Not to take anything away from the investigating police, but they are usually not sufficiently trained to make these exact determinations.

Parkewreck.jpg (11694 bytes)
Photo 1
This pickup struck the trailer's right rear duals. Note rotation to the left
caused deepest penetration to the driver's side.

As was also the situation in a case I'll discuss later, this accident involved a second vehicle underriding this trailer after the pickup had impacted it --- between 8 and 10 seconds later, That driver (who survived - the pickup driver did not) didn't recognize the hazard either, because on impact with the pickup, the semi had stopped, still blocking most of the opposing lane. Its headlights were still shining at the oncoming traffic, and the driver of the car had no visual clues until about the last three to fourseconds before impact. She also left about twenty feet of pre-crash skids. Despite all of this, the Trooper determined that both the pickup and the second vehicle, the car, were "at fault". The pickup driver had an over-the-limit blood alcohol and was "DUI". In a really inventive conclusion, the Trooper determined the car's driver to also be "at fault" because he found a box of KFC strewn about the floorboard of the car and presumed she was driving while eating --- ("DWE"?). She denied it, but that remained his conclusion.

In most cases, the trucking company will have their adjusters, and sometimes reconstruction engineers, on the scene while it is still intact. With all due respect to the police, it has to make a difference with these people on the scene talking to them during their investigation.

In any underride case, it is apparent that the driver of the vehicle striking the semi trailer didn't see the trailer in time to avoid the collision. In some cases, that may be wholly or in part due to significant driver inattention or impairment. In a nighttime underride, however, there arealmost always other factors that are the same or similar to those described above.

As an investigator, your job is to document vehicle damages, roadway evidence (skids, gouges, fluid stains, etc.), obstructions or other impediments to vision, roadway character, witnesses' observations and physical evidence of vehicle actions prior to impact and all of the related matters that may become disputed issues. (Before starting your investigation, read Jack Murray 's article again.) It is imperative that you inspect the scene at the same time of night, under similar weather conditions and moon phase, if at all possible. Videotape the scene from the perspective of the semi driver as it would appear prior to beginning the entry onto the highway from the side road. Eye level for the driver will be between 7-1/2 and 8 feet.

Never, ever, accept the police version before conducting your own investigation, but do make contact with the police investigator(s) and develop a rapport. Identify all ownership or lease interests in both tractor and trailer. There may be separate insurance policies. Obtain the semi driver's driving history (or histories). Check with both state and federal Departments of Transportation for any investigations and photographs. Obviously, visit your local newspaper and TV stations for any photos or footage that might be available, and if they won't release the material at that time, have your attorney client put them on notice to retain all negatives and raw footage. Also, put the trucking company on notice to not destroy or otherwise dispose of any potential evidence. Use the word "spoliation"--- they understand that. Recommend, and strongly, to your attorney client that a reconstruction engineer be brought in as soon as possible and that a computer animation of the crash may be necessary.

Several factors justify these expenses: the injuries are usually catastrophic, the truck driver almost always bears much, if not all, of the responsibility for the crash, and the trucking company carries insurance limits which justify the major effort needed to make an adequate recovery on behalf of your clients or their survivors.

In closing, I should note that in every case cited above, the drivers of each of the vehicles which underrode the semi-trailers were determined by the police investigators to be "at fault." Nevertheless, after thorough investigation and subsequent discovery processes, substantial recoveries were made on behalf of all plaintiffs.


1 NHTSA online at

2  Rear End Protection, CFR 49 Part 393.86 (1989) (effective Jan 1,1953)

3 ibid. (1)

4 Safety & Health, November 1995 (Study sponsored by NHTSA in mid-1980's)

5 ibid. (pages 71-72)

6 CFR 49 Part 393 Subpart B Sec.393.11 and CFR 49 Part 571 Subpart B Sec 571.108 (Available online at http:// frwebgate 1. access. gpo. gov/cgi-bin/)

7 Comprehensive discussions of the anatomy and physiology of the human eye are available in any encyclopedia

8 Florida Statute 316.237 (Requirements may vary slightly from state to state)

9 F.S. 316.238

10 ibid.

Recommended sites for further study of the underride problem:

1. Large Truck Safety Facts

2. Tractor-Trailer Underride - Another Look - and Another (Joseph E. Badger)

3. 3M Easy- To- Use Conspicuity Kits Make Trailers More Visible

4. Marking Time (Conspicuity Markings)


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Robert L. Parke, CLI, is a Life Member and officer of NALI. He may be contacted at his office in Monticello, FL. Ph: 850-997-2284.


Copyright 1998 by Robert L. Parke. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, to include photocopying and recording, or by any information storage and retrieval system, without prior permission in writing from the author.

Originally published in the May 1998 issue of "The Legal Investigator, The Official Journal of the National Association of Legal Investigators, Inc." (NALI.)  Http:// .