Accident Reconstruction – Hydroplane


A Mercury Mountaineer sport utility vehicle was exiting a right, downhill curve on I-77 when it hydroplaned on the wet roadway.  Full braking was applied by the driver, and the Mountaineer slid straight through the end of the turn and into the grassy center median, where it struck a cable median barrier and post.  Upon striking the post, the post bent over and as the Mountaineer slid over the cable barrier, the top cable wire became caught on the right rear suspension and snapped, causing the Mountaineer to turn sideways as is slid into the southbound lanes where it was struck on the driver’s side by a southbound GMC pickup truck.  The issue was to determine if the cable barrier had been installed improperly which allowed the Mountaineer to enter the opposing lanes where the collision with the pickup occurred.

Introtech Accident Reconstruction Services

James Crawford of Introtech Accident Reconstruction was retained to reconstruct the accident on behalf of the company that installed the cable median barrier.  Mr. Crawford, who is an accredited accident reconstructionist and holds a B.S. in electrical engineering and M.S. in Aeronautical Engineering, provided an analysis of the crash sequence to determine why the driver lost control of the Mountaineer, the speed at which it struck the cable median barrier, and whether the construction and/or installation of the cable median barrier contributed to the cause of the crash.

There was a heavy rain falling at the time of the crash causing the roadway to be wet with standing water in places, specifically at the location where this crash occurred.  Hard rain and standing water are situation hazards that require particularly cautious driving because the greater the depth of water on the roadway, the greater the risk for hydroplaning.

“Hydroplaning” occurs when the tire either partially, or in the extreme, completely separates from the road surface, and the tire rides on the water film.  This is termed to be hydrodynamic lift where there is a significant reduction or, as in this case, a total loss of traction forces.  When there are no traction forces available, no braking or side forces exist between the road and tires, rendering the vehicle uncontrollable.

Mr. Crawford inspected the Mountaineer and discovered that three of the vehicle’s four tires had virtually no tread left.  Bald or nearly bald tires have little or no tire tread (grooves) that are designed to channel water away from the tire so that it can keep contact with the road surface.  If the water cannot be evacuated from under the tire quickly enough, the tire will lift off the surface and be supported by only the water, resulting in loss of steering and braking forces.


Hydroplaning can occur more readily when the car drives through areas of standing water.  Each tire of a passenger car traveling at 60 mph must remove ~one gallon of water per second from the road to maintain its grip on the road.  The less tread on a tire, the less the tire can channel water away from the tire.

Mr. Crawford prepared a scale drawing of the crash scene with police measurements of key evidence points.  Using that scale drawing Mr. Crawford calculated that the initial speed of the Mountaineer was ~67 mph on a roadway with standing water.  At such a high speed the Mountaineer was virtually guaranteed to hydroplane, especially with bald tires.  Mr. Crawford’s calculations and analysis confirmed that the Mountaineer struck the cable median barrier such at an angle and speed that it was likely that it would have penetrated the cable median barrier.

Mr. Crawford found that the construction of the cable median barrier that was penetrated during this crash was in conformance with the plans of State Project V318-77-157-90.  It was was installed and maintained per plan and specification in accordance with West Virginia DOT Division of Highway standards.  The work performed by the construction company that installed the barrier was inspected and approved by the project engineer during installation and upon completion in accordance with West Virginia DOT Division of Highway standards.  Mr. Crawford found that the work performed by the contractor was as per plan and specification and was NOT in any way a contributory or causal factor in this crash.

To learn more about Introtech accident reconstruction process, read our car accident reconstruction page.