85th Percentile and ABQ Speed Cameras

CABQ has an “Automated Speed Enforcement” (speed cameras) website with details and compiled statistics on the program. Details/stats such as this:

That’s right, only just over 20% of drivers have been within the speed limit on the sections of Montgomery, Gibson, Unser, Lead, and Coal, noting that some cameras have been up longer than others and there are none on Lead/Coal right now due to high-profile thievery.

So the data-gathering in a work-in-progress, but is already interesting in comparison with that basis for decades of U.S. road engineering, the “85th Percentile” standard. Roadways have been designed and speed limits determined by taking the speed 85% driven at/below and determining that as the speed limit.

Taking the pathetically low 21.3% driving within the speed limit in the data gathered so far, and the whopping 72.8% of drivers going 1-10 mph over the posted limit, it’s hard to tell exactly where we get to 85% total, but it sure as hell is higher than the posted speed limit. Likely quite a bit higher.

So, should we raise the speed limit on these streets? That would be the “85th Percentile” argument, particularly in cases where drivers don’t experience variables such as “sight distance and obstructions” noted in this generally pro-85th Percentile explanation. My guess is that a poll of ABQ drivers would indicate strong support for raising speed limits on these and any other roads/stroads/highways in/around town. And those folks have decades of “85th Percentile” mentality in their corner, even if they’ve never heard of the professional road engineering standard.

They also have the sad fact that somewhere around 40,000 Americans die in traffic crashes every year, with 2021 estimates putting the total on the north side of that. Traffic deaths are trending down in many countries, but not here in the Land of the 85th Percentile. While the overwhelming majority of jurisdictions and road engineers still look to the 85th Percentile for speed limit insights, engineer Charles Marohn and the folks at Strong Towns approach the 85th Percentile and speeding nexus much differently:

Of course all the roadways in ABQ have been designed and speed enforced using the flowchart method on the left above. And undoing decades of standard engineering will be expensive and unpopular for reasons that extend beyond the expenditure of public funds.

From a political perspective, and everything from my viewpoint is political, a majority of drivers speeding and rather immense financial and political costs to slow those drivers down, often against their personal and political will, is a very hard combination. One feels Mayor Keller would never have spent the political capital needed to argue for speed cameras if not for his rather easy reelection and start of a second term. And fundamental change to the street design of, say, the airplane runway that is Gibson Blvd, is unfortunately, but perhaps correctly, perceived as a political bridge way, way too far.

Infinitely more popular would be cracking down on the small minority of those going 11-59 mph over the limit in the pie chart starting this post. That 5.9% is a perfect political mouthful for more extreme prosecution than the current $100, civil not criminal, fine or community service. Teasing out a way to differentiate penalties for these extreme offenders will go a sizable way toward making automated speed enforcement a permanent part of the political/roadway architecture of our fair city.

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