Why do Advisory Speed Signs have "MPH" on them?

[BrosephTX]

I've always wondered why Advisory signs of all the signs are the only ones to specify "MPH" when speed limits, school zone signs, and warning signs with integrated advisory don't?

Is this simply a lingering specification left over from the the attempt at Metrification?

[US 89]

If I had to guess, I’d say it’s because a small yellow sign with just a number on it would look weird. All those other signs have other text or pictures on them.

Of course, that doesn’t stop Europe from posting their speed limits in red circles without any other text.

[DaBigE]

Likely because there are other black on yellow plaques (albeit seemingly rarer), that have xx-FEET on them. In theory, there shouldn't be any ambiguity, since the plaques with feet measurements are usually in the hundreds of feet.

What is somewhat odd is that the newer "uni-signs" for curves and turns (W1-1a, W1-2a) do not have MPH on them, but the uni-signs for exits and ramps (W13-6, W13-7) do. Both sign types have arrows on them, so one would think that there shouldn't be possible confusion with distance or route markings.

[BrosephTX]

Likely because there are other black on yellow plaques (albeit seemingly rarer), that have xx-FEET on them. In theory, there shouldn't be any ambiguity, since the plaques with feet measurements are usually in the hundreds of feet.

What is somewhat odd is that the newer "uni-signs" for curves and turns (W1-1a, W1-2a) do not have MPH on them, but the uni-signs for exits and ramps (W13-6, W13-7) do. Both sign types have arrows on them, so one would think that there shouldn't be possible confusion with distance or route markings.

Oh you mentioning route markers reminded me Wyoming's route shields are Black on Yellow squares, which makes me wonder why the FHWA allows them to do that since they look just like advisory speeds.

[wanderer2575]

Likely because there are other black on yellow plaques (albeit seemingly rarer), that have xx-FEET on them. In theory, there shouldn't be any ambiguity, since the plaques with feet measurements are usually in the hundreds of feet.

What is somewhat odd is that the newer "uni-signs" for curves and turns (W1-1a, W1-2a) do not have MPH on them, but the uni-signs for exits and ramps (W13-6, W13-7) do. Both sign types have arrows on them, so one would think that there shouldn't be possible confusion with distance or route markings.

Oh you mentioning route markers reminded me Wyoming's route shields are Black on Yellow squares, which makes me wonder why the FHWA allows them to do that since they look just like advisory speeds.

Wyoming route shields have a "Wyoming" text across the top and a ride-'em-cowboy graphic on the bottom.  Anyone confusing them with speed advisory signs should not be behind the wheel.  At the risk of derailing the topic, I'll note that some amount of common sense (an increasingly obsolete concept) applies.

(But insert your own "Gee, officer, good thing I wasn't on Route 96!" joke here.)

[Mapmikey]

They didn't always have the MPH...

This was Virginia's style from the 1950s-70s.  Only a relative handful still exist anywhere outside of some independent cities who like them.


March 2014

[paulthemapguy]

On speed limit signs, the fact that the number represents a speed is obvious given the context.  On a supplemental advisory speed sign, it's not obvious because nothing else on the sign is saying anything about "speed."

The warning signs with the curve symbol and the number on the same panel are meant to be placed immediately along a curve; and not in advance, where you're supposed to place a regular curve sign with an advisory speed placard below it.  By the time you get to the sign with the number and the curve shape on the same panel, you should have already seen a warning sign in advance of the curve with the "MPH" placard, making the context of the number clear.

[jakeroot]

On speed limit signs, the fact that the number represents a speed is obvious given the context.  On a supplemental advisory speed sign, it's not obvious because nothing else on the sign is saying anything about "speed."

I think this hits the nail on the head. Our signs are not designed like the Vienna system, so we don't have any designs that speak for limits (in the Vienna system, that would be any round sign with a red border with a number in the middle). So we are forced to use supplemental language to give the number meaning.

Alternatively, instead of MPH, we could use "ADVISED" or "ADVISORY". Either way, it gives the number meaning beyond that of just a curve sign with a plaque below it without any additional text. I personally would prefer we not use "MPH", because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

[hotdogPi]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

[wxfree]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

That doesn't make sense. You can't enforce a warning sign.

Also, you can't be issued a ticket based on something in a driving manual. It has to be written in law. So find the law, and post back (please).

One of the TxDOT manuals explains a theory of the interpretation of advisory speeds.  The law in Texas is different, because all speed limits are technically prima facie, but I think the interpretation of advisory speeds could still be the same.  The real speed limit in Texas is "reasonable and prudent."  Massachusetts uses the term "reasonable and proper."  This applies regardless of the numerical limit and regardless of whether that limit is absolute or prima facie.  Under Texas law, the numerical limit reflects either a legislative default or (at least on state highways) engineering judgement of what is a "safe and reasonable" speed, which would be "reasonable and prudent" under good conditions.  Even without legislative enactment, an advisory speed is still an engineering judgement on what speed is reasonable and prudent under good conditions.  A speeding violation could be charged based on the basic speed law (reasonable and prudent), not based on a speed being in excess of the advisory speed, but based on a speed being in excess of what is considered reasonable and prudent in the judgement of the highway engineers.  Because of the prima facie nature of Texas speed laws, the speed limits and advisory speeds are somewhat in the same category.  TxDOT's Speed Limits web page actually says "Speed limits are posted primarily to inform motorists of the speed considered reasonable by a majority of drivers on a particular roadway," rather than saying that a speed in excess of the numerical limit is a violation of the law.  Source: https://www.txdot.gov/driver/laws/speed-limits.html

I described Texas law because I'm familiar with it and because it helps to explain the theory.  Under a prima facie speed limit setup, speed limits and advisory speeds are somewhat in the same category. Each is enforceable as an engineering judgement of what speed is reasonable and prudent.  In a state with absolute numerical limits, the prima facie speed limit reasoning still applies to advisory speeds.  In Massachusetts, advisory speeds inform law enforcement as to what speed is considered to be reasonable and proper under good conditions, and that basic speed law applies regardless of what numbers are placed on any signs.

Edit: I wrote that with the assumption that Massachusetts had absolute speed limits, based on a list I saw, but the details are more complicated.  "Massachusetts limits are prima facie except on roads that belong to the Massachusetts Turnpike Authority or the Metropolitan District Commission."  Still, I think what I wrote is technically correct.  In this form it can be applied to any state, so I'll leave it as it is.

Another edit:  I found the manual.  It describes the principle much more succinctly than I did, because I love long and drawn out background.  It says: "From the standpoint of enforcement, when a regulatory speed zone has been established and signs are posted, the speed values shown on the signs are the maximum lawful prima facie speeds. An advisory speed sign serves to advise drivers of safe speeds that are recommended for certain roadway conditions, such as horizontal curves. It does aid the enforcement officer, however, in determining reasonable and prudent speeds. A driver might be cited for exceeding the posted value of an advisory speed zone on the grounds that they were driving at a speed that was not reasonable and prudent for the conditions existing at the time and location."  at the bottom of this page: http://onlinemanuals.txdot.gov/txdotmanuals/szn/regulatory_and_advisory_speeds.htm

[hbelkins]

North Carolina commonly posts signs saying "Begin 35 1000 Feet Ahead." No "35 MPH." Just "35."

[DaBigE]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

That doesn't make sense. You can't enforce a warning sign.

Unfortunately, not all police know that and/or prey on the fact that most drivers are too dumb to know the difference in meaning of the signs. A former coworker of mine got pulled over for "speeding" in a construction zone based on an advisory speed. Double the fine thanks to the construction zone enhancer. Needless to say, she was pissed when I told her she could have fought the ticket and easily won. I've also heard of police departments ticketing people driving too fast through roundabouts based solely on a posted advisory speed. That also happens to be the most frequent instance of people not knowing what the sign means as they claim everyone is breaking the speed limit approaching a roundabout. 15/20 is highly advised, but you certainly can go through faster.

Many other places, it's a secondary enforcement. Meaning, if you lose control, cross the centerline, or otherwise end up off the road in the advisory segment, you'll likely get docked for speeding (too fast for conditions, or some variant), in addition to your crash.

[jeffandnicole]

...I personally would prefer we not use "MPH", because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

By the books, you are supposed to slow down to no faster than the advisory speed.

It's really annoying when there's one off ramp near me that you can do 60 on, in a 25 mph advisory zone.  Thankfully most people are well aware you don't have to do anywhere near 25, but even 40 mph seems slow on that particular ramp.

[PHLBOS]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

Which can be challenged and the ticket thrown out of court.  Such a ticket dismissal at a then-Fast Lane tool booth was the reason the posted advisory 15 MPH signs posted at the booths were all replaced with the more standard (& legally enforceable) SPEED LIMIT 15 signs.

Yes, I'm well aware that other roads in the Bay State still use advisory signs as speed limit signs (very ill-advised IMHO) but such is not legally enforceable even if the number on the sign is equal to the assumed speed limit on a road (example: a 30 MPH advisory panel along a road in a thickly-settled area).  In that case, the ticket issued for doing say 40 in a thickly-settled district limit of 30 would be based on violating that state law (implied speed limit) not the posted 30 MPH advisory speed sign.

[roadman]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

That doesn't make sense. You can't enforce a warning sign.

Unfortunately, not all police know that and/or prey on the fact that most drivers are too dumb to know the difference in meaning of the signs. A former coworker of mine got pulled over for "speeding" in a construction zone based on an advisory speed. Double the fine thanks to the construction zone enhancer. Needless to say, she was pissed when I told her she could have fought the ticket and easily won. I've also heard of police departments ticketing people driving too fast through roundabouts based solely on a posted advisory speed. That also happens to be the most frequent instance of people not knowing what the sign means as they claim everyone is breaking the speed limit approaching a roundabout. 15/20 is highly advised, but you certainly can go through faster.

Many other places, it's a secondary enforcement. Meaning, if you lose control, cross the centerline, or otherwise end up off the road in the advisory segment, you'll likely get docked for speeding (too fast for conditions, or some variant), in addition to your crash.

In Massachusetts, the speed posted on an advisory speed plate cannot be enforced as a speed limit, even as a secondary offense.  The catch in construction zones is that, as the 'double fines' law is written, you can be cited for driving at a speed above that which is 'reasonable and proper' for conditions, which is generally interpreted as faster than the advisory speed that is posted.

[hbelkins]

About 40 years ago, a rookie state trooper wrote a whole bunch of speeding tickets in my home county for people driving 55 mph in an area marked with a 45 mph advisory speed. Those tickets got thrown out of court.

Ironically, the speed limit in that stretch of road was lowered to 45 a couple of years ago.

[vdeane]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

That's certainly what they wanted, but the courts threw that out.  The result was nearly every advisory speed in MA replaced with regular speed limit signs.  That's why the speed limit on many roads changes every 200 feet.

[roadman]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

That's certainly what they wanted, but the courts threw that out.  The result was nearly every advisory speed in MA replaced with regular speed limit signs.  That's why the speed limit on many roads changes every 200 feet.

And I'm sure you'll find that the majority of those "regular" speed limits do not have an actual special speed regulation supporting them and are, thus, illegally posted.  This was a common practice in the City of Lynn when I was growing up there.

[bzakharin]

...I personally would prefer we not use "MPH", because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

By the books, you are supposed to slow down to no faster than the advisory speed.

It's really annoying when there's one off ramp near me that you can do 60 on, in a 25 mph advisory zone.  Thankfully most people are well aware you don't have to do anywhere near 25, but even 40 mph seems slow on that particular ramp.

There is an exit off a 65 MPH freeway onto a 55 MPH 2-lane road which become 4-lane as the exit lane continues onto the road that has a 25 MPH advisory. The curve is gentle enough that you can take the exit without slowing down to below 55 (i.e. no need to speed up afterwards). No one ever bothered me at the exit for not slowing to 25, though some others do slow down.

[doorknob60]

because some (read: a small group of people) seem to conflate the yellow plaque to be a definite limit.

It is a definite limit in Massachusetts, according to the driver's manual and traffic enforcement (yes, you can get a ticket for disobeying an advisory speed limit).

That doesn't make sense. You can't enforce a warning sign.

Unfortunately, not all police know that and/or prey on the fact that most drivers are too dumb to know the difference in meaning of the signs. A former coworker of mine got pulled over for "speeding" in a construction zone based on an advisory speed. Double the fine thanks to the construction zone enhancer. Needless to say, she was pissed when I told her she could have fought the ticket and easily won. I've also heard of police departments ticketing people driving too fast through roundabouts based solely on a posted advisory speed. That also happens to be the most frequent instance of people not knowing what the sign means as they claim everyone is breaking the speed limit approaching a roundabout. 15/20 is highly advised, but you certainly can go through faster.

I've seen in Nampa when they chip seal the roads, they often put up orange advisory "20 MPH" signs. Sometimes they even remove the normal speed limit signs (generally around 35). So you have some people (including me) trying to go the normal speed limit ~35 because it's still a fine speed, and then some people trying to go 20 because they think it's the speed limit. Kind of a mess sometimes. I think Ada County does something similar, but I don't remember the specifics.

[MisterSG1]

For the record, the ones in Canada, in Ontario at least ALWAYS show km/h.

I think of two types of advisory signs usually, the one warning of an upcoming turn and a speed underneath, and one that shows a ramp speed for a freeway ramp. (The latter, there isn't a universally agreed on version of how it should look in Canada).



While the one below is one you see for exit ramps in Ontario:



While this one for example is the one for exit ramps in Quebec:

[jakeroot]

While this one for example is the one for exit ramps in Quebec:

https://upload.wikimedia.org/wikipedia/commons/thumb/1/1a/Qu%C3%A9bec_D-120-55.svg/90px-Qu%C3%A9bec_D-120-55.svg.png

Replaced with "EXIT", this is what I see in BC. Apart from non exits, in which case...

http://www.th.gov.bc.ca/popular-topics/images/faqimages/w001-2002_30km.jpg

...this is the most common design. Which is of course no surprise since I can see you pulled the image from the BC MOT's website.