Before retiring as a S.C. State Trooper, and to this day, people routinely ask me, “How fast can I go before I get a speeding ticket?” Let me start by saying one mile per hour over the speed limit can subject you to a speeding ticket. While different officers have different standards, it is easier to talk your way into a ticket than to talk your way out of one. So, much like the number of licks to get to the center of a Tootsie Roll Tootsie Pop, the world may never know an exact answer to how fast you can go over the posted limit without a citation. A better question is ‘What is the benefit of exceeding the posted limit?’
During my 10 years on the Highway Patrol’s Multi-Disciplinary Accident Investigation Team, I was involved in 1000’s of collision investigations and reconstructions. I witnessed how increased speed influenced crashes and crash severity. Crunching the numbers as an accredited crash reconstructionist, I have charted information comparing what happens when you increase your speed above the set limit.
People believe 5 or 10 mph over the speed limit is acceptable, so I have compared those ranges using a reasonable perception-reaction time of 1.5 seconds. Perception-reaction could be faster, but it is unlikely with the distractions in a car. The vehicle’s condition is assumed to be excellent (especially the brakes), and the road friction value used is .75, a mid-range value for dry traveled asphalt. Considerations used in analyzing a crash are applicable in this study and yield a conservative assessment.
The time saved by increasing your speed is not enough to be a benefit to your travel. These times don’t take into consideration the obstacles, other than time, that will get between you and your destination to cause increased time. Stopping at traffic lights, getting bogged up in traffic, or any interruption will, obviously, add time; and those things, along with many more, can and will happen. The ability to shave 2 minutes off 15, 5 minutes off 30, or 10 minutes off an hour becomes a gamble; a gamble that you won’t add 15 minutes for a traffic stop, hours for a minor accident, days for a hospital stay, or the unfathomable loss from death. As the chart shows, you’re not really saving time relative to the risk.
In evaluating a motor vehicle crash, the distance the vehicle skids is used to calculate speed; therefore, you can use the speed of a vehicle to derive the distance required to stop. It only stands to reason that increasing speed increases both perception-reaction time and stopping distance. At 5 mph over the posted speed limit, your total distance to stop is increased by an average of 17%. That translates to an average increase of 36% if you travel 10 mph over the posted speed limit.
Many studies relate speed with increased chance of collision. Some also derive a scale to comparatively relate speed to DUI. Considering the time that you will be traveling, increasing your speed doesn’t improve your arrival time in a significant way. Along with increased reaction and stopping distance, there is a reduction in passenger safety equipment effectiveness, increased crash and injury severity, increased cost of repairs, and increased fuel consumption. According to the National Highway Traffic Safety Administration, in 2016 more than 10,000 people died in traffic accidents where speed was a factor – 27% of all fatal collisions. Bottom line: it’s not worth becoming a statistic to save a little time.
Aaron (Al) Duncan II, ACTAR, is a vehicle collision reconstructionist with Warren and President of SCARS. Prior to joining Warren, he worked for 23 years as a South Carolina Highway Patrol Trooper to include 10 years as a Multi-Disciplinary Accident Investigation Team (M.A.I.T.) member. Al is accredited as a Traffic Accident Reconstructionist by The Accreditation Commission for Traffic Accident Reconstruction. He investigated in excess of 1000 vehicle accidents and incidents, as a trooper. Then, as a member of M.A.I.T. for 10 years, he was involved in over 1000 detailed investigations and collision reconstructions. Al has testified multiple times in state courts and he has been court qualified as an expert in accident investigation and collision reconstruction. Al’s work expertise focuses on investigating and reconstructing vehicle collisions involving single and multi-vehicles, animals, pedestrians, motorcycles, heavy trucks, and commercial vehicles. He is also a skilled user of forensic mapping technology and computerized collision diagramming software for collision scene analysis. Al is experienced in the data download and analysis of airbag black boxes (Crash Data Retrieval Units) in automobiles, pickup trucks, and SUVs. He holds a Bachelor of Science Degree in Political Science from Lander University in Greenwood, South Carolina and completed the Law Enforcement Basic Program at the South Carolina Criminal Justice Academy in Columbia, South Carolina.