Could a lower speed limit have saved a skateboarder’s life?

275-BMW-WILLIAMS-CRASHThe St Augustine Police Department has not yet provided the requested copy of the Florida Traffic Crash Report for last week’s fatal crash that killed 16-year-old skateboarder Ja Williams.

As the investigation and community discussion continues about the continuing mobility, access, and congestion issues for vehicles and pedestrians in St Augustine, Historic City News readers are asking if a lower posted speed limit on four-lane Anastasia Boulevard would have saved the teenager’s life.

“We are escalating our efforts to obtain the crash report from the police so that we will have the most reliable data, even though Records Technician Jeanette Baker was apparently not trained in §316.066(2)(b) F. S.,” Historic City News editor Michael Gold said Saturday.  “Crash reports held by an agency may be made immediately available to the media.  The Department of Highway Safety and Motor Vehicles provides us with this information daily, unfortunately local police assumed investigation of this traffic homicide and they don’t understand how to comply with Florida’s public records laws.”

First, it is important to understand that this traffic homicide occurred on Anastasia Boulevard — a leg of State Road A-1-A; and, as we learned in the Bridge of Lions brouhaha, the Florida Department of Transportation owns and makes the decisions for it.

Since the teen’s death, we are aware of an un-official assessment of the dynamics of this crash by a local traffic engineering expert, Mark Edwards.  Working without the benefit of the actual crash report, Edwards made some assumptions and arrived at an opinion on the speed limit and its potential to have prevented this death.

These assumptions were made:

  1. Pedestrian on skateboard proceeding in southerly direction crossing Boulevard.
  1. Pedestrian does not stop or pause in median area
  1. Traffic proceeding east and west approximately at speed limit
  1. Distance traveled from northern edge of eastbound Anastasia to approximate point of impact (POI) approximately 25 feet
  1. No evidence of braking on part of striking vehicle

Edwards made the following analysis as he applied what we believe happened in the Anastasia Boulevard crash:

  • Typical speed of skateboarder – 10 mph (approximately 15 feet per second)
  • Travel time for skateboarder from edge of median to POI approximately 2 seconds (25/15) = 1.7 seconds
  • Assuming striking vehicle at 40 mph (59 feet per second) – it would be approximately 118 feet from eventual POI when skateboarder left the median area (about 3 stripes on roadway)
  • Distance required to stop from 40 mph at maximum brake force for naive driver – 77 feet + (2.2 x 59) = 207 feet – driver would not be able to stop before striking skateboarder.
  • Perception reaction time for driver of striking vehicle including time to achieve 0.7 g’s stopping force approximately 2.2 seconds – time to stop once braking at maximum brake force approximately 2.6 seconds – total elapsed time required approximately 4.8 seconds — under the assumptions of this scenario, driver would have needed to perceive the need to stop when the skateboarder was just entering the westbound lanes of Anastasia – not a likely possibility
  • Effect of lower speed limit of 30 mph on opportunity to avoid collision – at 30 mph (44 feet per second)

Striking vehicle would be approximately 88 feet from eventual point of impact when skateboarder left median area of Boulevard.

Time and distance required for striking vehicle to come to a stop assuming driver attentive but surprised by the skateboarder entering the eastbound lanes of Boulevard. is approximately 4 seconds (2.2 seconds to achieve maximum brake force + 1.95 seconds to come to a stop at .7 g’s) – collision is still unavoidable because of the actions of the skateboarder

Edwards points out that the pedestrian establishes the gap between themselves and approaching traffic when they enter the roadway.  This critical gap is under the control of the pedestrian, not the driver.

For a two-lane roadway, the gap that 50% of pedestrians would accept and 50% would reject is 8.5 seconds, according to Edwards.

“In this case, the pedestrian accepted a gap of about 2 seconds if my assumptions are correct,” Edwards wrote this weekend.  “Lowering the speed limit would have no benefit because it is the skateboarder that is in control of the decision.”

Edwards’ analysis concludes that the driver could not have prevented this collision — even if the speed limit were lowered.

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