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In the past, we talked about how important it is to understand the 85th Percentile. It’s a tough concept, but once you get it under your belt your knowledge of how to make roads safe increases significantly.

The other concept that tends to confuse people at first is the 10 mph Pace.10-mph-pace-image

The 10 mph Pace is the speed at which the majority of cars are going on a stretch of road. While the 85th Percentile is the maximum speed that 85% of drivers will not exceed, the 10 mph Pace is the range of how fast those cars are actually going.

For example, if the 85th Percentile is 37 mph, the 10 mph Pace is typically around 25-35 mph.

However, the pace can change throughout the day depending on how busy the road gets. The 85th Percentile, on the other hand, remains the same regardless of congestion.

For example, if there is congestion in the morning at 7 a.m., the 85th percentile stays the same because it’s the maximum speed drivers are willing to travel. However, the average speed of the driver on the road at that time will drop. This can be seen by placing a sensor on the road and collecting the data. If the 10 mph Pace decreases at a specific time of day, there is likely congestion.

What this means for law enforcement is that looking at the 10 mph Pace helps understand whether specific cars are speeding or are safely going the average speed. If the speed limit is at the higher end of the 10 mph Pace, that means the majority of the cars will go slower than the speed limit. If the pace is toward the lower end of the range, then cars will be traveling above the limit.

An ideal situation would look like this:

  • The 85th Percentile is 37 mph
  • The 10mph Pace is 23-33 mph
  • The speed limit is 25 mph

The example above shows that vehicles are trending around the speed limit and the speed limit is set correctly. Using these data points could also justify raising the speed limit. If the 85th Percentile was 45 mph, the 10 mph was 33-43 mph and the speed limit was 25 mph, many cars would be traveling above the speed limit and those at the speed limit could be unsafe.

What do you think about the 10 mph Pace concept? Could knowing it be helpful on some of your patrol routes? Let us know!

by Marshall Barto at All Traffic Solutions


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