Speed Traps Set to Increase Revenues
Speed Traps and the 85th Percentile
How are speed limits set in the first place?
A Michigan State Police Lieutenant made news recently when he confirmed publicly a fact many have long suspected: in many places throughout the state, speed limits are set artificially low. Speed limits that are too low result in speeding tickets which equate to revenue for cash strapped local units of government. This assessment was then confirmed by a local police chief whose jurisdiction includes a stretch of one of the most heavily traveled roads in the state. As the road crosses into his city, the speed limit drops to a point that, as he admits, likely cannot be justified. The city has no intention of raising the speed limit, however, because of the revenue it generates for the city. A state lawmaker believes that the problem of artificially low speed limits has gotten so out of hand that he has introduced legislation that will force local communities to correct speed limits that are set too low. The question then becomes, how are speed limits set in the first place?
Justified on the basis of public safety
The right to set speed limits is an exercise of the police power of the state and is therefore justified on the basis of public safety. Speed limits are intended to reflect a reasonable and safe speed that will facilitate the safe and orderly flow of traffic under normal conditions. Research has shown that the majority of motorists operate their vehicles in a safe and reasonable manner, hence, traffic laws and speed limits that reflect the behavior of the majority of motorists are the most successful. The inverse is also true: traffic laws and speed limits that arbitrarily restrict the majority of motorists encourage violations, lack public support and rarely achieve the desired result. Speed limits are not to be set based upon unreasoned opinion but upon thorough traffic engineering studies. Those studies include an analysis of such factors as the number and types of accidents that have occurred, the number of cars traveling the road, their speeds, the presence of pedestrians, the physical condition of the road surface, hills, curves, number of lanes, driveways, intersections, and so on.
A certain speed is intuitive to the majority of motorists
The primary method for establishing a proper, realistic and safe speed is something known as the 85th percentile. The 85th percentile speed is the top speed at which 85% of motorists will drive on any given road at any given time without regard for slower traffic congestion or weather. The 85th percentile speed is the speed that most motorists consider safe and reasonable, pretty much without regard for the posted speed. In fact, research has shown that artificially raising the posted speed above the 85th percentile does not necessarily result in faster speeds, just as artificially lowering the posted speed below the 85th percentile does not necessarily result in lower speeds. It is not really a conscious decision to drive at a certain speed but one that is intuitive to the majority of motorists.
Established traffic engineering practices
Michigan law provides that all traffic control devices placed anywhere in the state must conform to the national standards set forth in the Manual on Uniform Traffic Control Devices and must be placed in accordance with a written traffic control order. This includes the setting of speed limits and speed limit signs. Sections of the Manual provide that speed limits are to be set based upon traffic engineering studies made in accordance with established traffic engineering practices. Further, speed limits should be within 5 mph of the 85th percentile speed.
Unrealistic speed limits are not followed
While realistic speed limits are generally followed, unrealistic speed limits are not. Absent strict, continuous, and visible enforcement, artificially low speed limits will be ignored. And any adherence that does result is limited to the immediate time and immediate area of the enforcement (i.e., speed traps). If you find yourself getting a ticket in an area where the posted speed limit just doesn’t seem to make sense, you might consider asking the municipality for a copy of the traffic control order and the engineering studies upon which the speed limit was based. If the speed limit is not within 5 mph of the 85th percentile speed, and, no other unique and distinguishing factors exist, you just might have a defense. You might also want to keep an eye on the pending legislation.
Duane L. Reynolds