The Median Barrier Allowed Trucks Rollover And Override It

NTSB.Gov, Jan 12, 2006

In 2002, heavy trucks accounted for between 26 and 28 percent of the 125,300 vehicles that traveled daily on the accident segment of I-95. However, the 32-inch-high standard portable concrete median barrier in use at the accident site was designed only to redirect cars and private-use trucks under 4,400 pounds. Safety Board investigators calculated that the 1996 Freightliner, including the compressors and the flatbed semitrailer, weighed over 42,000 pounds and had a center of gravity approximately 4 inches higher than the top of the median barrier.

In addition:

• The cross-slope of the depressed median placed the truck at an angle, which increased its propensity to roll toward the barrier, creating an unstable condition.
• The unembedded barrier allowed the truck to tip and override it.

High-performance median barriers at least 42 inches high are heavier than standard portable barriers and are designed to redirect heavy trucks, such as the 1996 Freightliner. Barriers exceed the center-of-gravity height of heavy trucks, making them less likely to overturn or be overridden during a collision.

Yale University and traveling north in the left lane collided with and underrode the left side corner of the 1996 Freightliner tractor flatbed semitrailer. Following the impact, the Chevrolet disengaged from the semitrailer and entered the median, skidded along the concrete barrier, and came to rest about 450 feet northeast of the semitrailer. The driver and three passengers in the Chevrolet were fatally injured. The surviving occupants were seriously injured. Witnesses reported that at the time of the accidents, light snow was falling, the roads were wet and icy, and snow covered the roadway shoulders.

The National Transportation Safety Board determined that the probable cause of the 4:50 a.m. accident was the 1996 Freightliner’s loss of lateral stability, probably due to the operator driving too fast for conditions and to the presence of black ice on the roadway. Contributing to the accident were the inadequate roadway treatment provided by the Connecticut Department of Transportation in response to inclement weather and also its failure to provide a median barrier capable of preventing crossovers by heavy vehicles.

The probable cause of the 5:01 a.m. accident was the failure of the Chevrolet driver to identify and avoid the flatbed semitrailer due to fatigue, in conjunction with the distraction from the median crossover accident in the southbound lanes. When the driver of the 1996 Freightliner tractor flatbed semitrailer lost control of his vehicle near MP 26.6, the truck entered into a counterclockwise skid toward the unpaved and depressed highway median. It collided with and overrode a 32-inch-high portable concrete barrier system. The collision overturned and laterally deflected five barrier segments toward the south and visibly cracked one segment. The Safety Board examined issues associated with the type of barrier used at the accident site and its placement on an unpaved surface.