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Hydroplaning is frequently alleged to be a cause of vehicular traffic accidents. This is because many persons, even law enforcement personnel, may not know the technical definition and criteria for hydroplaning. Also, hydroplaning may be alleged when in fact the cause of an accident is actually carelessness, driving faster than roadway and weather conditions permit, bald or otherwise defective tires, and other such factors that are not "Hydroplaning," per se. The traffic accident which is described below demonstrates a method for calculating depth of rainwater runoff on a highway pavement, in order to determine whether or not hydroplaning may have occurred.

The roadway at the scene of the accident consists of two lanes of pavement in each direction separated by a 6-foot wide raised median. The accident involved an automobile, Vehicle #1, which was proceeding westbound on an approach embankment to a bridge (an upward slope) when the accident happened. The vehicle suddenly made an abrupt left turn, crossed the raised median, impacted the guardrail on the outside of the opposing eastbound lanes and was struck by Vehicle #2, an eastbound vehicle. The two vehicles became joined together and traveled back across the raised median to a final location on the westbound traffic lanes.

Mr. Helmer visited the site of the vehicular traffic accident. He took photographs, made measurements and made other relevant observations of the roadway, in relation to facts and allegations that were stated in the various case documents.

The driver of Vehicle #1 was alleged to have lost control of her vehicle when its right front tire encountered ponded water on the westbound roadway pavement. Three governmental reports were obtained which provided information on rainfall rates and distributions during the time period preceding the accident. Statements concerning magnitude and distribution of rainfall indicated that, "...light rainfall (no more than 0.04 inches) occurred at the accident site between 2:30 and 2:40 p.m.

This was an hourly rainfall rate of 0.04 inches/10 minutes x 60 minutes/hour = 0.24 in./hr. This rainfall rate was used in calculations that were made by Mr. Helmer.

The westbound traffic lanes at the accident site have an upward slope in the westbound direction of travel. They are on an asphalt-paved earthen embankment approaching a bridge. The longitudinal slope of the asphalt pavement is 6.5%; the transverse slope is 2.5%; and the combined diagonal slope was calculated to be 6.96%.

Mr. Helmer used a five-gallon bucket to pour water on the westbound roadway pavement in the vicinity of the location where Vehicle #1 reportedly went out of control. The water followed a diagonal path along the 6.96% combined diagonal slope, as would be expected.

Calculations were made to determine depth of flow of rainwater runoff for locations of Vehicle #1's left and right tires, if traveling in the left lane, or right lane, of the westbound roadway. The depth of flow of rainwater runoff at the accident location was calculated using a commonly accepted hydrologic and hydraulic procedure. The depth of flow of the rainwater runoff was calculated to range from 0.196 in. to 0.454 in. for the left tire in the left traffic lane and the right tire in the right traffic lane, respectively. These values were used by the attorney and other persons assisting him with the case, to determine probability of hydroplaning (or not).

The case was settled favorably for Mr. Helmer's client, which was the Defendant State Department of Transportation, on the basis of Mr. Helmer's review of documents, Site Inspection, calculations and Expert Report.

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Mr. Ray G. Helmer has been a Licensed Professional Engineer in several states for more than 50 years. He has extensive experience in engineering design of streets, highways, and specifically traffic signals. He has participated in approximately 300 Expert Witness cases for both plaintiff and defense attorneys. He is available for traffic engineering investigations, expert reports, depositions and trial testimony.

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