Theory: MUTCD-Compliant Speed Traps

[paulthemapguy]

I wanted to talk about signs preempting drivers to anticipate an upcoming reduction in speed.


0600380 by Paul Drives, on Flickr

As many of you know, the most important distinction to understand about the MUTCD's verbiage is the level of permission or restriction given among the items, "Standard", "Guidance", "Option", and "Support."  Essentially, standards are "shall" statements; guidance comes in the form of "should" statements, and options are "may" statements.  When it comes to signs announcing an upcoming drop in speed, entering a town or in any other application, the MUTCD states that an advance notice of a decreased speed zone SHOULD be used for drops in speed exceeding 10 mph.  In a country where speed limits are only ever divisible by 5mph, this indicates a decrease in speed by 15mph or greater.

To dodge this guidance in places where the speed limit drops by 20mph, jurisdictions, who don't like being limited in generating speeding ticket money, will place a short buffer zone with a speed limit 10mph less than the higher speed (i.e. halfway between the high and low speeds).  For example, instead of placing a "35 mph speed zone ahead" sign in a 55-mph zone before the start of an upcoming 35mph zone, a town looking to nab more speeding ticket money will put a short 45-mph zone in between.  This is done to cause two sudden speed limit drops, catching drivers by surprise twice, since the staggered 10-mph drops no longer require the use of anticipatory signage ("speed zone ahead").  My theory for why various locales will do this is so they can sidestep MUTCD guidance to throw drivers off and create speed traps (or "generate ticket revenue" if you want to put it more favorably (I don't)). 

My questions are:
1. Do you agree that this is done deliberately to generate more speeding tickets, and
2. Do you know any examples of this in your area?  Instead of a 55-to-35 did they put up a 55-45-35 to sidestep the recommendation of putting up "speed limit 35 ahead" signs?  It can also be a 50-40-30, 45-35-25, or even a 55-45-35-25.

[ran4sh]

Plenty of local jurisdictions (as well as some states) already don't comply with the MUTCD, so I think they wouldn't care to comply with it regarding speed limits either.

It's actually good engineering practice to not have sharp speed limit decreases like 55 to 35. My state still posts the reduced speed ahead sign to warn of a 10 mph reduction such as 55 to 45 and then 45 to 35.

[JoePCool14]

I'm sure there are some locations that do this. Sometimes the intermediate speed section is comically short, and definitely raises some eye brows. On the other hand, some places it actually makes sense to drop the speed limit gradually. Maybe you hit a section of big-box commercial properties before reaching the town itself.

I think the guidance should probably be adjusted to include changes of 10 mph, so that only changes of 5 mph don't need to be warned about.

In terms of examples, I'm almost certain there are sections of US-20 in northwest Illinois that do this gradual drop sort of thing.

It's actually good engineering practice to not have sharp speed limit decreases like 55 to 35. My state still posts the reduced speed ahead sign to warn of a 10 mph reduction such as 55 to 45 and then 45 to 35.

I would agree with this.

[riiga]

1. I doubt it.
2. It was widely practiced here. I'll quote myself from a recent thread about sequential speed limits where I elaborated on it.

This kind of change [in speed] was the standard here until 10 km/h increments were introduced in 2007. Before that, the only speed limits here were 30, 50, 70, 90 and 110 km/h and changes were almost always (30->)50->70->90(->110) or vice versa as changes of more than 20 km/h at a time required announcing the change in advance (apart from on- and off-ramps on motorways) so it made more sense to sign 90->70->50 than 90->50 (in 200 m)->50. Now speed limits go from 30 to 120 km/h with 10 km/h increments and while this practice is still common (but more recently with 40->60->80) sequential speed limits are disappearing here as it makes little sense to use such small increments on most roads.

[kphoger]

France does this at service areas, too.  It reduces to 90 km/h, then 70 km/h, then 50 km/h.  At some, you can see all the speed limit signs at once.

As for this being done on purpose in the USA, I'm not so sure.  I don't doubt that some officers might take advantage of it after the fact, but that doesn't mean it was set up that way on purpose.

[hbelkins]

I've heard lots of complaints over the years about big, sudden drops in speed limits. One that got a lot of attention ages ago in MTR was on US 460 in West Virginia, approaching the Virgina state line, where the speed limit dropped from 65 to 45.

[jeffandnicole]

First, what are you defining as a speed trap?  A simple reduction in a speed limit isn't it.

One large reduction that's being discussed is around the 295/76/42 interchange in NJ, where I-295 went from 55 mph to 35 mph.  This wasn't to generate more speeding tickets, but rather, if you continued at 35 mph, chances are you were going to crash into the wall on a very sharp curve.  I've never read or heard from a single person they got a ticket in those 35 zone, which re-enforces the fact the signs were there because the former advisory signs weren't being taken seriously.

[Dirt Roads]

I've heard lots of complaints over the years about big, sudden drops in speed limits. One that got a lot of attention ages ago in MTR was on US 460 in West Virginia, approaching the Virgina state line, where the speed limit dropped from 65 to 45.

This is kind of a holdover from when US-460 first opened and the eastbound lanes jumped up on the old route on the south side of the New River before turning left across the old New River bridge.  The 40MPH dropped to 25MPH before making the right turn into Glen Lyn (assuming that Glen Lyn was on the south side next to the power plant back then).  When VDOT built the parallel bridge, it seemed like the connection to the railroad grade route on the north side didn't have any spirals that would support higher speeds.  Over time, it seems like these curves have smoothed out to support higher speeds, and the Glen Lyn congestion on both sides of the river is pretty much gone these days.

[I-55]

More often than not I get the opposite, where on my way out of town I get a slow speed increase. This is actually pretty smart as it keeps more aggressive drivers from accelerating more quickly and loudly.

[johndoe]

If it makes you feel better, I've never personally had a fellow engineer try to increase the number of tickets given.  AFAIK there's no incentive for an engineer to do so.  You're talking about people who work on multi-million dollar jobs, I don't think they care to screw drivers so their department might stand to gain a few thousand dollars in a few years.  Speed limits can be more of art than science (to an extent) but this isn't the deciding factor.

Now...has it ever happened?  Probably.  Maybe smaller public works departments could generate more on a percentage basis?  But I would think most speed reductions happen on routes controlled by an entity big enough they don't have any reason to play such games.

[RobbieL2415]

What about "Speed Zone" signs?

[NE2]

It's not a trap if you're clearly told what the limit is and choose to exceed it.

[Scott5114]

If it makes you feel better, I've never personally had a fellow engineer try to increase the number of tickets given.  AFAIK there's no incentive for an engineer to do so.  You're talking about people who work on multi-million dollar jobs, I don't think they care to screw drivers so their department might stand to gain a few thousand dollars in a few years.  Speed limits can be more of art than science (to an extent) but this isn't the deciding factor.

Now...has it ever happened?  Probably.  Maybe smaller public works departments could generate more on a percentage basis?  But I would think most speed reductions happen on routes controlled by an entity big enough they don't have any reason to play such games.

The way most governments are structured, the department that pays the engineers doesn't even benefit from the collection of traffic tickets. Traffic tickets either go to the police department or the general fund. In the latter case, traffic tickets are normally a comparatively small part of the revenue coming in, and only a small fraction of that money ends up funding the public works department anyway.

[kkt]

I don't see that much difference.  If the speed limit is dropping from 50 to 30 mph, you'll get two signs either way:  1 "speed limit 30 ahead" and a "speed limit 30", or a "speed limit 40" and then a "speed limit 30".  And, as posted already, the little one-block towns who are just trying to extract traffic fines ignore the MUTCD anyway.

[zachary_amaryllis]

I don't see that much difference.  If the speed limit is dropping from 50 to 30 mph, you'll get two signs either way:  1 "speed limit 30 ahead" and a "speed limit 30", or a "speed limit 40" and then a "speed limit 30".  And, as posted already, the little one-block towns who are just trying to extract traffic fines ignore the MUTCD anyway.

the towns along us 85 between greeley and denver are famous for this... and they all sport bright shiny new police cars. the speed goes from 65 to 35 or 40 for like a mile when you're going through town (eaton, i'm looking at you) and you almost have to stand on the brakes to get down to that speed.

and i think some are artificially low... there's a stretch of 287 right as you leave fort collins going north, signed at 45, but everyone does 50-55 through there, and thats what 'feels' right. seen lots of blue-light specials given out on that stretch.

[StogieGuy7]

I nominate WI 50, which drops quickly from 55 to 35 as it enters the village of Paddock Lake.  You can click the link below, but it's less than 1/4 mile from the advisory sign to the actual speed drop. And the cops know it and often sit and await their prey. 

https://www.google.com/maps/@42.5682083,-88.0894998,3a,75y,282.77h,84.5t/data=!3m6!1e1!3m4!1soZ6Lj82Vgw_CPF_uhsn-7w!2e0!7i16384!8i8192

By the way, 35 is absurd for this highway - it should be more like 40 or 45.