It is not uncommon for someone to run into the rear of a tractor trailer on the open highway. In fact there have been reports on critical problems of side and rear under-ride impacts for a long time. One news report shows how horrific these collisions can be, see:   In court we frequently hear everyone testify that the taillights on the trailer were on, which begs the question: "Why did the driver of the car run into the back, or side, of the tractor trailer?"

Part of the problem is driver expectation. What can a reasonable and prudent person expect when driving at night? Car drivers expect that trucks will obey the minimum speed limit if they are traveling on the interstate. If a tractor trailer is traveling below the minimum posted speed limit,  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. At 55 miles per hour (80.85 feet per second) the approaching car will cover 485 feet in only six seconds. At night it takes longer for a driver to see and react to unexpected situations in the highway. It takes a driver MUCH longer to realize that the tractor trailer isn’t moving, or is moving slowly, which is why almost 100% of these collisions happen at night.

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 the 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. It would take longer to brake.

Pre-collision skidmarks are rare. Occasionally investigators will find some, but the marks are usually not very long. This means that the driver identified the problem far enough back to brake, but too close to stop before impact.

It must be made clear that these cases are not situations where cars running  90-mph slam  into the rear of 65-mph tractor trailers. What happens is that the tractor trailers — often loaded, which slows their acceleration rates even more — merge too slowly into traffic. Such trailers generally get rear-ended when traveling 25-35 mph by unsuspecting motorists who may see the back of the trailer but appreciate neither their closing speed nor the fact that the rig is barely moving compared to other traffic. In a technical report for Transport Canada titled "The Perceptual Basis Of Heavy Vehicle Conspicuity And The Role Of Retroreflective Materials In Increasing Driver Decision Sight Distances," Brian Tansley and Will Petrusic of Carleton University’s Psychology Department stated it this way: "The dynamic aspect of control of a moving vehicle involves the visual perception of the driver’s own movement relative to the roadway and of the movement of other vehicles relative to his/her own."

Side collision cases are even worse because trucks in the United States are not required to have side impact guards, despite the trucking industry being aware of the problem for years. In fact in Europe side impact guards are required.  A recent case may change this in the United States. In Gregory S. Becker, et al v. Wabash National Corp., U.S. District Court, S.D. Texas No. C-07-115 The Judge allowed a case to go to the jury where the plaintiff’s alleged the lack of side guards caused the death of the woman who hit the trailer. 

My thanks to the Underride Network which is responsible for much of the content of this blog. See: