NTSB: Texas Motorcoach Accident Result of Roadway Design, Wet Pavement and Minimum Tread Depths

July 18, 2005

In a report adopted last week, the National Transportation Safety Board said that roadway design, wet pavement, and the condition of the tires were factors that led to the crash of a motorcoach, killing seven people two years ago in Texas.

On Feb. 14, 2003, a Central Texas Trails Inc. motorcoach traveling on Interstate 35 near Hewitt, Texas, ran off the road, crossed the median and collided with a Chevrolet Suburban traveling in the oncoming lane. Heavy rain, fog, and haze in the area had reduced visibility at the time of the accident.

As the motorcoach driver approached the crest of a hill he noticed that traffic was stopping ahead for a previous accident. He began to brake and move from the right lane to the left lane to avoid the stopped cars but another car moving into the left lane at the same time forced the bus driver to brake hard. The rear of the bus skidded and the driver lost control. Five motorcoach passengers, the Suburban driver and one passenger were killed in the accident.

The Board’s investigation determined that the wet pavement at the accident site, combined with Interstate 35’s roadway geometry, and a speed limit (70 mph) that exceeded the road’s design speed did not provide drivers with enough time to react and stop their vehicles, or avoid a collision.

The Board recommended that the Federal Highway Administration (FHWA) issue guidance to its field offices describing the inadequate stopping sight distance that can occur on roadways where hills exist along with low coefficients of friction and speeds higher than the design speed. The Board also identified the benefits of using variable speed limit signs to reduce speeds in inclement weather and further recommended guidance from FHWA on their use.

NTSB Acting Chairman Mark Rosenker noted, “Just because we can drive faster doesn’t mean we should. Speed limits need to realistically reflect safe driving conditions on a given road for the given situation.”

The Board recommended that the State of Texas inventory such highway locations and develop a plan to repave or make other improvements to the roadway. In another recommendation to Texas the Board recommended the installation of variable speed limit signs at locations where wet weather could produce a stopping distance greater than the sight distance.

The roadway was not the only factor contributing to the motorcoach’s loss of control. The Board determined that the low, but legal, tread depth of the rear tires were unable to channel the water out from between the tires and the roadway, further reducing the friction available. The Board recommended that the FHWA conduct research on the interaction between commercial vehicle tires and wet pavement surface to determine minimum frictional quality standards and tire requirements.

Research and testing have reportedly shown that placing tires with greater tread depths on the front axle of a vehicle creates an inherent safety problem in passenger vehicles, and would likely have the same effect on commercial vehicles.Yet Federal regulations require that the front tires of commercial vehicles have a greater tread depth.

Thus, the Safety Board recommended that the National Highway Traffic Safety Administration conduct testing on commercial vehicles to determine the effects of different tread depths, and that the Federal Motor Carrier Safety Administration change the tread depth requirements to reflect the results of the testing.

The Board’s report noted that the Texas Department of Transportation’s Pavement Management Information System does not adequately identify roadways where hazardous conditions exist when the pavement is wet. The Board also recommended that the Texas Department of Transportation revise their Wet Weather Accident Reduction Program to better identify areas where surface conditions and roadway geometry lead to dangerous conditions.

A synopsis of the report including a complete list of the Conclusions and Recommendations can be found on the Board’s Web site, www.ntsb.gov.

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