August 24, 2021Case Highlight: Advisory Speed


            A crash involving a tractor-trailer and a motorcycle occurred on a state highway, resulting in a lawsuit filed by the injured operator of the motorcycle. The crash occurred as the driver of the tractor-trailer turned left from the two-lane, two-way rural highway into a residential driveway. The tractor-trailer had completed the turn, but the motorcycle ran into the back end of the trailer as it was positioned on the driveway and out of the travel lane.

            The plaintiff sued the owner of the tractor-trailer, alleging that the driver made an unsafe turn into the driveway. The plaintiff also sued the state highway department, alleging that there was inadequate sight distance provided for the driver of the tractor-trailer to see the motorcycle.  


The highway in question is old and was designed before design speed was used in the highway design process. Using the posted speed limit of 55 mph, adequate sight distance was available for passenger cars, but not for large trucks. However, keeping in mind that large trucks are not typically used as the design vehicle, the state’s argument that adequate sight distance was provided (based on the posted speed limit) was valid. The state also argued that since the impact occurred when the tractor trailer was no longer in the travel lane, if the motorcyclist had stayed in the travel lane, that the crash would not have occurred.

            The owner of the tractor-trailer settled, recognizing that the driver violated a company policy of taking company vehicles home. Facts did not support the allegations against the state, with one unexpected exception. A ball bank test, which determines the advisory speeds in the field using a vehicle equipped with a ball-bank indicator and an accurate speedometer, was made on the horizontal curve. It was determined that the appropriate advisory speed was either 45 or 50 mph, depending on which test was accepted and which speed was selected. The plaintiff argued that had an advisory speed been in place, the operator of the motorcycle would have responded to signs, lowered his speed, and reached the crash site after the truck had cleared the roadway completely.  Hence, the crash would not have occurred.


            State highway engineers agreed that if the horizontal curve was tested, an advisory speed would have been posted along with a Curve Warning sign, although they did not believe that the presence of those signs would have made a difference in the crash involving a motorcycle operator familiar with the site.  Nevertheless, the state decided to settle the case.

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