Friday, July 25, 2014

Speeding, and Speed Limits

The speed limit on most roadways is set too low.  That's a given, and any traffic cop can tell you that when he (or she) is not in uniform.  The reason why is complicated, and fairly simple if you understand how traffic flows.  The simple fact is that most speed limits are set by political considerations, rather than the design of the roadway.

We've all seen it.  You're tooling along on a nice, level, well maintained roadway and you come into some town.  The speed limit deceases by some amount, usually 10-20 mph, and you slow through town.  So, we slow down and drive through town, until we get the outskirts, and we speed up.   The simple fact is that most of us would do that anyway, because towns have more traffic entering the roadway, and red lights, and small-town cops.  Who write tickets.  But most of us slow down going through town even though it is precisely the same roadway, built at the same time that the other, faster roadway was built.  It's a psychological thing.

I've taken traffic management courses over my career, and basic Traffic Management 101 teaches you about the 85th percentile, which basically says that you want to set the speed milt on a roadway so that 85% of the motorists will drive at or below the speed limit, and 15% of the motorists will drive at or above the speed limit.  As this article points out.
This “nationally recognized method” of setting the speed limit as the 85th percentile speed is essentially traffic engineering 101. It’s also a bit perplexing to those unfamiliar with the concept. Shouldn’t everyone drive at or below the speed limit? And if a driver’s speed is dictated by the speed limit, how can you decide whether or not to change that limit based on the speed of traffic?
The best method of setting a speed limit is to observe traffic from a place where motorists don't know that they're being observed.  Gather your data, and set your speed limit at the 85th percentile.  Then round up to the nearest 5mph (when have you ever seen a 57 mph speed limit).

Our cars are safer, our roads are safer, and in many cases, the speed limit remains the same.  Why is that?  simple, it's politics.  One of my very dear friends is the mayor of a small town, and the US government recently upgraded the US highway that runs through town.  What was before a poorly maintained two-lane highway is now a beautiful, new four-lane highway,  Outside of town, the speed limit is 65.  Hit the town boundary and the speed limit drops to 45 mph for less than a mile, until you hit the other boundary.  Why"  Safety"  Not likely.  It's the same level, new, four-lane highway.  More likely the reason is revenue.
The other reason speed limits may remain low, which John Bowman, Communications Director of the National Motorists Association strongly insists on, is that cities and police departments use traffic citations as a revenue generating tool. As Bowman says, when speed limits are artificially low, it’s easier to give out citations and pull in fine revenue.
Go read the whole article, but the simple fact remains that if you're interested in traffic safety, you have to understand how traffic flows, and that in most of our country, cities and towns, the speed limit is simply set too low.


Eaton Rapids Joe said...

So, did you just get a ticket?

Kidding aside, I once got pulled over by the police chief of Sunfield, Michigan when I was going 10 over on M-43.

He told me that he was a Dad. He said kids, his kids, did not always think before chasing a ball out into the street.

We sat there for about 20 minutes while he did the routine. His flashers flashing.

He let me go with a warning, but none of the other drivers could know that. I suspect that everybody who passed us during that 20 minutes drove the speed limit through Sunfield for the next month.

He gave me a warning. He was a GOOD cop. Law Enforcement is about changing behaviors. I never sped through Sunfield or Mulliken, Michigan again.

Sadly, he lost his job when a babysitter reported a home invasion. He responded but the babysitter said she never called. The cop went away. The next morning the babysitter claimed she had been raped.

Much later, it was determined that the "rapist" was her on-again-off-again boy friend. The cop was a casualty of their relationship.

Sometimes, life sucks.

Pawpaw said...

Silly boy, no, I haven't had a ticket in over 20 years. I am a paragon of virtue and scrupulously observe all traffic laws.

Old NFO said...

Snerk... Yeah, right... :-) And the 85th percentile STILL will get your butt a ticket if you're over by 15... The Navy actually closed two bases in Georgia, one in Brunswick and one in Albany, because of targeting of Navy personnel for speeding tickets/fines.

Anonymous said...

Pawpaw that another way of saying you have been lucky?

It is about revenue.


mostly cajun said...


I'm up and down US 165 in Louisiana all too regularly. Let's see, some of my favorite places: Fenton, Kinder, Woodlawn, Ball, Pollock, I seldom pass through those without seeing one of their brave public servants protecting and serving some poor schmuck who exceeded the speed limit.

I know better. Lots of people don't.

Texans driving through Fenton and Kinder on the way too and from that casino pay a lot of revenues to those little towns between I-10 and the casino.


Goatwhiskers said...

Then there's always Livonia that rakes in over $40,000/mo according to reports, along with Krotz Springs, Port Barre, and others. GW