What is the 80th Percentile for Drivers?

Here is an attempt to explain the concept of the 80th percentile as it relates to driver behaviour.

Hopefully you have experienced situations on an interstate where the flow of traffic is seamless. Everyone is moving smoothly and unimpeded. You are not overtaking cars in front and no one is on your tail. Lane changes are simply an exercise in drifting in and out as everyone is driving the same speed. Compare this with situations where everyone is jousting. Cars don’t seem to be moving ahead and drivers behind are pushing your tail or trying to pass. Lane changes are an exercise in straining your neck around and taking your life in your hands. You need to constantly change speeds or accelerate or brake.

Imagine that you are in your new sports car and you have been waiting for the right moment to test out its acceleration and speed. You are all alone on an open highway with no speed limits. You don’t have to worry about other motorists or speed traps. You can drive as fast as your heart desires with no restrictions. Your adrenalin flows as your roadster roars through the gears and the engine is full throttle and effortlessly takes you to 100 mph. You wonder how fast this baby can go as you push the accelerator to the floor. You feel the power beneath you as your car leaps ahead and now you are at 130…145… 160! Wow, this is absolutely exhilarating!

At some point; howevever, your hands tighten on the steering wheel and your heart starts to race. You begin to wonder. Is it wise to push a new car to such high speeds? Will I blow my engine? What if other cars do enter the highway further on ahead? If I hit a pothole or something on the road at this speed, it could cause me to wipe out. I know this baby can go fast but I don’t necessarily want to continue at this speed indefinitely. I love driving this car fast but I don’t want to be on edge the whole time; I just want to enjoy being in it.

Based on these precautions, you reduce your speed until eventually you settle into a speed that you feel comfortable. This is what the 80th percentile about. It is the collective mindset of a group of drivers on the highway at any one time based on road conditions, visibility, traffic, confidence that drivers have in their cars and their driving ability. Four out of five (80%) will settle into what they perceive as a comfortable level for the conditions. It is a flow which does not compromise their ability to get to their destination in reasonable time yet provides them with sense of confidence and security. They drive at a certain speed and dictate the general flow of traffic. This speed may be higher or lower than the posted limit but that is the speed that the consensus of drivers feel is the most efficient.

Drivers who do not move with this flow are an impediment to everyone else. If they are moving slower they are in the way and others will try and pass them. If they are moving faster they are constantly changing lanes or tailgating and trying to pass everyone else. This creates an imbalance and irregular behaviour as the majority tries to adapt to the few who are not within the consensus flow of traffic.