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Objects in Motion

Defending the tractor-trailer versus passenger vehicle rear-end collision.

May 09, 2019 Photo

Sir Isaac Newton knew a thing or two about what happens to an object in motion. One of his observations: “Change in velocity depends on the mass of the object.” If only physics was included on a driver’s licensing exam.

A loaded tractor-trailer weighs 35 tons. The average passenger vehicle weighs two tons. Given that the velocity of a mass describes the rate of occurrence or action, will two masses (for this discussion, vehicles) having the same span of distance within which to employ deceleration (but having two completely different weights) arrive at the same location at the same time traveling at the same speed?

Anyone involved with automobile claims knows all too well the scenario of a passenger vehicle changing lanes into the path of a tractor trailer with only two car lengths (or less) of space between vehicles. Frequently this results in a rear-end collision, with the tractor-trailer not having enough distance for the needed reduction of speed to safely slow the truck. Investigating officers may ticket the driver of the tractor-trailer, as the appearance of rear-end collisions in many jurisdictions is considered a prima facie, or self-evident, infraction with the assumption of fault routinely attributed to the driver of the tractor-trailer.

Since a determination of fault that includes an investigation of velocity would likely be considered outside the traditional field officer’s investigation, it is not likely that the claims industry is going to significantly alter the future of at-scene fault determinations. That said, a savvy safety manager at the scene on the date of loss, or an investigating claims handler, can incorporate into her handling some investigative techniques that could produce benefits in the defense of a presumptive attribution of fault in a rear-end collision. These techniques include the following:

Depth and distance of yaw marks. A 70,000-pound tractor-trailer screeching to a halt will leave in its wake grooves and tire burn marks that will reveal its driver’s desperate attempt to avoid a collision. The length and depth of these grooves can provide important information depicting how far and how fast the truck decelerated.

Point of contact. If a tractor-trailer is attempting to avoid collision or jack-knifing by rear-end collision with a passenger vehicle, frequently the point of contact to the passenger vehicle will be off center. The damage to the passenger car will have a slanted impact, gradually decreasing in depth to the outer bumper where the strike marks veer outward as the truck swerves to one side or the other.

Distance between ramp lane end and collision site. In the case of the passenger vehicle attempting a highway merger in front of a tractor-trailer, there may be a measurable distance from lane end to accident site that suggests an insufficiency of allowable stopping distance. For instance, if the other driver arrives at the on ramp and attempts to merge in front of a tractor-trailer with 100 feet of allowable stopping distance, and just as the passenger vehicle arrives in the lane all traffic slows from 55 to 40 mph, the tractor-trailer will not have adequate available distance to slow to 40 and avoid a rear-end collision. This could potentially shift some of the burden of fault to the passenger vehicle. An investigating claims handler needs to review the stopping distance between lane merge to the point of collision to determine sufficiency of allowable stopping distance.

Surrounding traffic speed. Most of us have observed the lone car that jumps into a lane at 50 mph only to slam on the brakes, while the surrounding traffic has already slowed to 40 mph or less.

Data recorder downloads. Preservation-of-evidence letters generally are intended to lock down an insured’s business vehicle after an accident. However, consider that evidence preservation is a two-way street. When the exposure and damages are high, the preservation of both commercial and private vehicle computer databases can yield a world of information about the pre-incident actions of both vehicles. Frequently, a passenger vehicle involved in such a loss will be totaled and the event data recorder (EDR) will become unavailable when the vehicle is sold at auction. For EDR evidence to be recovered, time is of the essence. The adverse party must be put on notice that its insured’s EDR will be sought as evidence. Such downloads can reveal acceleration, deceleration, speed at point-of-contact, and other crucial information to support an improper lane change by the passenger vehicle.

Theories and Practice

To properly consider the allowable stopping distance of any vehicle, legislators have discussed a calculable precedent—commonly referred to as Assured Clear Distance Ahead (ACDA)—that describes the distance ahead of any vehicle within which that vehicle may be safely brought to a halt. According to the ACDA methodology, there is a measurable span for safe deceleration applicable to each vehicle.

The Federal Motor Carrier Safety Administration (FMCSA) says a loaded tractor-trailer requires a stopping distance of two football fields, or 720 feet, to stop. Federal safety guidelines now incorporate the application of “thinking distance” before considering stopping distance, indicating that a driver must see and recognize an approaching hazard (thinking distance) before the calculation of stopping distance begins to apply. These are wonderful applications of theory, but how can we use them to defend and mitigate insurance claims for rear-end collisions?

In triaging motor vehicle accidents, it is essential that the on-scene responders proactively construct a defense from the outset. This means taking scene photographs that depict distance, signage, lane markings, merge markings, skid marks (including depth), fuel spills, shoulders, and greenways.

If safety permits, the on-scene field investigator should measure the distance from on ramp lane merger to on ramp lane closure (when the access lane decreases to the existing outside lane). An accident responder can attempt to speak to the investigating officers at the scene to ask if available stopping distance has been considered. The driver of the rear vehicle, if appropriate, may relay to the investigating officer an occurrence description that includes her concerns about the other vehicle’s lane merge with insufficiency of available stopping distance.

In taking statements from adverse drivers, a claims professional should include questions concerning the allowed span of car lengths in front of the vehicle occupying the outside lane prior to the adverse driver’s integration into that lane. Both drivers might be questioned concerning the traffic in front of the allowed span of car lengths.

If a driver accesses the outside lane in heavy traffic, the allowed space may still be insufficient if the traffic in front of the merging vehicle brakes, thereby compressing or diminishing the available stopping span and further requiring emergency braking. These lines of questioning—especially if this information can be illuminated during the investigating officer’s on-scene evaluation of liability—can create questions of negligence that may open the door to a more favorable apportionment of fault.

About The Authors
Michelle A. Maggs

Michelle A. Maggs, AIC, is senior casualty adjuster at Crawford & Co.  michelle_maggs@us.crawco.com

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CLM’s Transportation Committee provides education, training, and solutions on significant current commercial and personal transportation issues facing insurance carriers, corporations, and other entities and individuals.

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