Least Common Speed Limit

[sprjus4]

For North Carolina, 60 mph is likely the answer.

Over the past decade or so, 60 mph has become more commonplace to replace 55 mph on rural divided highways and on urban freeway segments and is only growing.

[Caps81943]

Virginia:

20 - very uncommon (a select few neighborhoods and cities)
25 - exceedingly common (nearly every city and neighborhood street)
30 - somewhat rare (most commonly used on suburban roads that are somewhat minor but too good condition to be a 25)
35 - common (many urban and highly developed suburban arterials)
40 - somewhat rare (I've mainly seen it on highly developed yet well-maintained suburban roads or sparsely developed yet windy suburban arterials)
45 - very common (most suburban arterials that aren't highly developed and many curvier rural roads)
50 - somewhat common (major highways with too much development to be 55), definitely the most common x0 in the state
55 - exceedingly common (default speed limit, many major highways)
60 - somewhat rare (a few rural divided highways, a few urban freeways)
65 - somewhat rare (similar to Utah's 75, freeways that sit between 55-60 and 70
70 - common (most rural freeways)

[Scott5114]

It might be a good idea to first decide which ones can be eliminated: 30, 55, 65, probably 75. And personally, I'd say both 35 and 40 are out, as those are both very common in suburban areas. Any others?

You can probably rule out 45 too. It's used fairly frequently in Oklahoma for "arterial without a lot of development" (example).  And I know of at least one rural county that has 45 as its default for county roads–hundreds of miles of paved roads at 45 mph.

You can probably rule out 70 too. That's a max speed limit in a lot of states that are too scared to post anything higher (and many of the current 75 states had 70 before they had 75). I think 70 is the default two-lane speed limit in Texas.

[TheHighwayMan3561]

60 in Wisconsin,  more limits at 55, 65 and 70.

In an upset, I would also put 30 on this list for Wisconsin since 25 is generally used in places most other towns/cities in the US would post 30.

[interstatefan990]

I believe many Northeastern states (NJ comes to mind) are in a similar predicament.

I think it varies. For example, New York's law reads like this: "Speed limits should be 55 miles per hour, but the DOT may establish a limit of up to 65 miles per hour."  Whereas with other states, like NJ that you mentioned, I guess it would be per se illegal to post 60.

I also can't picture a 50 mph, but I'm less confident in my take there.

I feel like 50 is used fairly sparingly - but maybe I just miss the 50 MPH Zones

50 is one that you don't see a lot around here–I can only think of one 50 MPH zone, and that's SH-9 (divided expressway with traffic lights).

I feel like the theme I'm getting here is that in a lot of places throughout the United States, 50 MPH is used frequently as a "fall-back"  speed limit where it would normally be posted at 55 or higher but a lower limit is necessitated due to roadway design, traffic levels, intersections, approaching developed areas, or other reasons. However, this is definitely not universal as a handful of states have statutory 50 mph limits for various types of highways, NJ, VT, MA, OH, DE, MD, WA included. It would be the default limit in those states on those specific roads, provided the DOT hasn't lowered or raised it, which is rare.

If what Caps81943 said about Virginia's 50 zones being somewhat common isn't representative of the rest of the states, then I don't know, maybe 50 MPH is in the running for the least common speed limit in the USA. The question is whether it would come down to competing with 60 MPH or with 20 MPH for that title.

[jakeroot]

Washington State (WA) is easy: 65. It is only used over Snoqualmie Pass, and along some select two-lane highways.

Additional thoughts:

20 is exceedingly uncommon apart from two scenarios: non-arterials in Seattle, and school zones. Unfortunately, both include a ton of mileage, so likely not the least common.

40 isn't exactly common, but it's decently rare. 35 and 45 seem more common.

55 may have been popular, but it's not anymore. 99.99% of freeways were increased to 60 or 70. 55 is primarily used on two lane highways now, but even then, 50, 60, and 65 are also used on two lane highways, and I might argue that 50 and 60 are at least as common as 55, if not more.

[TheStranger]

California...

20 is extremely uncommon

25 is the standard "low speed street" number, whether in urban areas, or in the suburbs

30 is another "low speed street" number

35 to 45 is the range for most standard divided arterials and other similar roads

50 to 65 are the common divided highway/expressway/freeway speeds, with 55 being the standard for a fast two-lane road, and for some older freeways (i.e. US 101/Bayshore Freeway in San Francisco, which then goes up to 65 immediately at the city limit going southbound).

70 is reserved for rural freeways out here, i.e. I-5 in the San Joaquin Valley on the West Side Freeway alignment, and US 101 in southern Monterey County.

60 probably thus is the most uncommon as 50-55 or 65 are the usual freeway numbers.

[hotdogPi]

Relevant thread: https://www.aaroads.com/forum/index.php?topic=11967

[jemacedo9]

Pennsylvania:

20 - almost unheard of
25 - residential, very common
30 - sometimes residential, relatively uncommon
35 - default urban, very common
40 - rareish? Kind of like 30
45 - any highway with any amount of development, pretty much - very common
50 - quite rare
55 - Default and I hate it but common
60 - literally illegal
65 - About half of rural interstates, quite common
70 - The other half of rural interstates, also quite common
75 - can we have these, please?
80 - Dreamland

And if they wanted fewer people driving 40 because of depth perception issues... that's an excellent reason to abolish the 30mph speed limit. 

Southeastern PA has quite a few 40 MPHs. There are more 35s and 45s then 40s, but not a lot more.  30 and 50 are definitely rare.

[sprjus4]

Relevant thread: https://www.aaroads.com/forum/index.php?topic=11967

It's not the same.

[kphoger]

I-25 has a 60 mph zone on the south side of downtown, but off the top of my head, that's the only one in Colorado.  There are no 70 mph zones that I'm aware of.  I also can't picture a 50 mph, but I'm less confident in my take there.

Here are a few I've personally driven:

CO-47 around Pueblo is 60 mph. 
US-50 west of La Junta is 60 mph.
US-550 south of Montrose is 60 mph
It also resumes 60 mph south of Ridgway.

50 mph is, I think, more common in Colorado.

For example, US-50 leaving Lamar to the northwest is 50 mph.
Also, US-550 closer to Ouray is 50 mph.
And CO-145 northwest of Placerville is 50 mph.

In fact, I saw so many 50 mph speed limit signs on that trip that I'd consider it to be one of the most common speed limits in Colorado.  Either 35 or 50 seemed to be the standard for anything in the mountainous half of the state.  Heck, here's a spot on US-50 along the Gunnison River that I was just guessing might be 50 mph, and sure enough it is!

As for 70 mph, I can't recall having personally seen any such zones in Colorado, but I wasn't on the lookout for them.  However, I do see that CDOT recently (2019) lowered the limit to 70 mph on a seven-mile stretch of I-70 in Grand Junction:  old vs new.

[zzcarp]

What is the least commonly posted speed limit in the US? This excludes anything below 20 MPH or above 80 MPH, and temporary work zones.

My guess would be 60, I don’t know if it’s just me but the only times I’ve ever seen that anywhere in the Northeast was approaching a couple of population centers along I-95/Maine Turnpike. Maybe it’s more common elsewhere?

I-25 has a 60 mph zone on the south side of downtown, but off the top of my head, that's the only one in Colorado.  There are no 70 mph zones that I'm aware of.  I also can't picture a 50 mph, but I'm less confident in my take there.

Chris

I can think of several 50 mph speed zones in Colorado off the top of my head. CO 128/120th Avenue through much of Broomfield and Westminster (except between Wadsworth and Main Street) is 50. Also, I-70 through both the Eisenhower/Johnson Tunnels and Glenwood Canyon is 50.

As for 60 mph zones, much of CO 7 between I-25 and Brighton is 60 mph. Same for part of US 36 entering Boulder from the southeast and north of Boulder. Another spot is CO 67 between Woodland Park and Deckers.

As for 70, that is the least-used one in Colorado. Other than the new I-70 signage kphoger listed above, I know of no interstates signed with it. A few years back they raised E-470 and then most of the Northwest Parkway from 70 to 75. The only remnant I'm aware of is on the Northwest Parkway where they left the last mile between US 287 and 96th Street as 70.

[ilpt4u]

There is a 50 MPH zone in the town I live in...and a 20 MPH zone in the town I work in. Both are small towns in Southern Illinois

I still say 50 is pretty uncommon, 20 also

[Ketchup99]

If this was my dream-world, almost every 25 zone would become 20 or 30 overnight (or more, in some cases) - little residential roads shouldn't be more than 20mph, and collector or arterial routes ought to mostly be 30. Plus, every town's got that one (or more) deer-in-the-headlights 25mph zone that should be 35 or 40.

So in that world, 25 is the least common. But in our world, it's very likely 20mph.

[kphoger]

There is a 50 MPH zone in the town I live in...and a 20 MPH zone in the town I work in. Both are small towns in Southern Illinois

I still say 50 is pretty uncommon, 20 also

Speaking of southern Illinois (and ignoring the parameters of the OP), can you think of any towns other than Eldorado that have 15 mph?  That one always drove me nuts.

[sprjus4]

I don't know of any 60 mph zones in Georgia off the top of my head. Other than the 70 mph interstate maximum, it's relatively rare to see an x0 speed limit in the greater Atlanta area.

I-20 through Atlanta is posted at 60 mph.
US-41 between Griffin and Barnesville is also posted at 60 mph.

[NWI_Irish96]

Indiana-

Interstates: 50 mph (Indianapolis in downtown) 60 mph speed limits (Evansville and right before the bridges in Louisville)
Divided highways: I don't know...
Two-lane highways: 50 mph speed limits (it's only used in busy stretches with a lot of driveways)

There are no freeways posted at 60 in Indiana. The Louisville approach goes 70->65->55. The Evansville approach doesn't get above 55.

I don't recall ever seeing 50 posted on a 4-lane non-freeway, but can't say for sure it doesn't exist somewhere.

50 is not uncommon on 2 lane roads but still has to be the least common speed limit in Indiana. There are plenty of 45, 40, 35, 30, 25, and 20 in cities and towns.

[WillWeaverRVA]

50 is relatively uncommon in Virginia. It seems to be more common in North Carolina (most of US 158 on the Outer Banks is posted at 50).

[index]

50 is relatively uncommon in Virginia. It seems to be more common in North Carolina (most of US 158 on the Outer Banks is posted at 50).

It might be just that area, I don't remember seeing 50 very much around here. I also hardly if ever see 40.

[zzcarp]

How about 10 mph like Eldorado Springs, CO?

[vdeane]

I'd say 50 is a better choice: Most places have some 50 zones, but there's nowhere where they're particularly prevalent.

Go drive in New England.  50 is everywhere over there.  Vermont in particular uses it as the default and won't sign 55 on anything that isn't limited access.

[US 89]

I suppose I can break down Utah:

20 - mostly limited to a handful of high density downtown streets, plus school zones
25 - default residential, also in some downtown areas
30 - common on residential collectors and downtown roads
35 - very common on highways through sizable rural towns, as well as some denser urban arterials
40 - pretty much the default urban arterial, also common on highways through small towns and on 2-lane mountain roads
45 - relatively rare, found mainly on slightly less developed/dense urban arterials
50 - common on high grade arterials that maybe don't meet expressway status
55 - default rural limit, along with many urban expressways and certain exurban/mountainous parts of rural 2-lane highways that would otherwise be higher
60 - relatively rare and not really a defined class - these are pretty much either "would be 55 but too good for that" or "would be 65 but too bad for that"
65 - very common: off-interstate statewide maximum, including rural flat 2-laners and most non-interstate freeways, as well as mountainous or substandard interstate segments
70 - default on urban interstates
75 - uncommon and limited to rural interstates that were too mountainous/exurban to be bumped to 80
80 - statewide maximum, the norm on rural interstates

[jeffandnicole]

I believe many Northeastern states (NJ comes to mind) are in a similar predicament.

I think it varies. For example, New York's law reads like this: "Speed limits should be 55 miles per hour, but the DOT may establish a limit of up to 65 miles per hour."  Whereas with other states, like NJ that you mentioned, I guess it would be per se illegal to post 60.

NJ created a no-mans land in respect to a 60 mph regular limit. But first, some quick history:

During the NMSL, the only speed limits on the books were statutory limits if signs weren't posted:  25, 35 & 50 mph.  Other roadways could be higher or lower based on "engineering & traffic investigation".  But here's the thing...55 was never a stated limit in the statute, even during the NMSL.  NJ was forced to reduce their fastest limit to 55 during the NMSL, but it was never made into law.  When the state wanted to consider raising the limit to 65, they should have been able to do so based on the existing law, which only would have needed an engineering and traffic investigation.  Instead, it became a long, drawn out affair with an amended statute to allow 65 mph.  It also would double fines (which, being NJ, was really about a 185% increase, not a 200% increase) for those speeding at 10 mph over the 65 limit, but also doubled fines for those speeding 20 mph or greater for other limits. 

(In a technical sense, the 65 mph law is just the "Sixty-Five MPH Speed Limit Implementation Act".  Nowhere does it say it's an absolute top limit.)

This puts a regular 60 mph speed limit in a strange position:  Someone going 75 mph in a 65 zone may pay a double fine.  Someone going 75 mph in a 55 zone may pay a double fine.  But someone going 75 mph in a 60 zone wouldn't be subjected to the double fine.

This doesn't apply to work zones, as all speeding fines are doubled. Thus, this allows 60 mph to be used as a work zone without any of the fine issues referenced above.  (Note: Doubled fine don't quadruple in a work zone for speeding)

[webny99]

I'd say 50 is a better choice: Most places have some 50 zones, but there's nowhere where they're particularly prevalent.

Go drive in New England.  50 is everywhere over there.  Vermont in particular uses it as the default and won't sign 55 on anything that isn't limited access.

Whoops... Yes, I did forget about Vermont and their 50 mph default. That might be the only state where 50 is that common though, as almost everywhere else uses 55 or higher as their rural default.

[vdeane]

I'd say 50 is a better choice: Most places have some 50 zones, but there's nowhere where they're particularly prevalent.

Go drive in New England.  50 is everywhere over there.  Vermont in particular uses it as the default and won't sign 55 on anything that isn't limited access.

Whoops... Yes, I did forget about Vermont and their 50 mph default. That might be the only state where 50 is that common though, as almost everywhere else uses 55 or higher as their rural default.

It's really common in MA, NH, and ME too.