Why Portsmouth, NH? Why not Danvers?

January 2, 2014 2:10 PM

I live off Interstate 95 in Massachusetts, and if I want to go north, the sign indicates 95N Portsmouth, NH, and if I want to go south, the sign says 95S Providence, RI. How are these seemingly random cities chosen?

There are closer "big" cities than either of these and it's gotten me to wondering: how are these route designations made? How is it decided that Portsmouth is the northern destination and not, say, Salem, MA? All along interstate highways, who decides what cities are written on signs and on what basis? (And I've been to Portsmouth and yes, it is lovely, but not a reason you'd get on a highway from the Boston area.)

posted by kinetic to Grab Bag (13 answers total)

Salem isn't on I-95.
posted by Chocolate Pickle at 2:12 PM on January 2, 2014 [3 favorites]

Response by poster: Salem is a bad example. Okay then, Burlington, MA. Or Reading. Woburn.
posted by kinetic at 2:15 PM on January 2, 2014

They aren't primarily for locals. They are there to help interstate travelers (vacationers and non-locals) to get their bearings more-or-less right fairly quickly. If you were heading to Salem you'd already be on the lookout for your exit number, but if you were heading up to Maine you'd know you needed to go through Portsmouth.
posted by gauche at 2:16 PM on January 2, 2014 [1 favorite]

Best answer: Apparently, they're called Control Cities.

The control city is typically on or close to the route of which is serves as the primary focal point. In exceptional situations, towns along prominent intersecting roads could serve as such, notably when the vast majority of traffic would turn off to that intersecting road.

Under the Manual on Uniform Traffic Control Devices, control cities must appear on the route signs:

At interchanges between freeways (example US-1 in gallery)
At separation points of overlapping freeway routes (example US-2 in gallery)
On directional signs on intersecting routes, to guide traffic entering the freeway (example US-3 in gallery)
On pull-through signs (example US-4 in gallery)
On the bottom line of post-interchange distance signs (example US-5 in gallery)

Since the towns on post-interchange distance signs are listed in ascending order of distance, the control city of routes in the United States is typically the most distant locality on the signs of a particular road.
posted by xingcat at 2:18 PM on January 2, 2014 [31 favorites]

Here's a list of the control cities used on the Interstate system. Last updated in 2004!
posted by theodolite at 2:26 PM on January 2, 2014 [4 favorites]

Anecdotally, I've lived in Massachusetts for almost five years, and I could not tell you where Woburn or Danvers is. I do know that New Hampshire is north, though. So, yeah, they're mostly for the benefit of non-locals.
posted by Metroid Baby at 2:28 PM on January 2, 2014 [1 favorite]

Although I do not have the knowledge that a couple of the responses have demonstrated, I have observed that the signs tend to switch off on the "control cities." In my area, driving from Detroit west, I might see Lansing on one sign and then Muskegon on the next.
posted by yclipse at 3:24 PM on January 2, 2014

Out west, in the emptier areas, there will often be a sign listing the next three "big" cities along the interstate, and the distance to each one. I remember once driving (probably on I-10) and seeing the third city listed was Los Angeles, some 300+ miles away. I assume that one was chosen because of the Pacific Ocean.
posted by benito.strauss at 4:58 PM on January 2, 2014

I wonder if the presence of the Portsmouth Navy Yard makes that a more appealing thing to list on a sign.
posted by rmd1023 at 7:28 PM on January 2, 2014

The Wikipedia article linked above mentions that cities (or towns) at a large intersection may be selected as control cities. This is why the otherwise unremarkable small town of Albert Lea, Minnesota gets such attention--it's where I-35 and I-90 cross each other.
posted by gimonca at 8:23 PM on January 2, 2014

They are the state of Massachusetts' boundaries, or at least that is what I have always assumed. Marking the signage in this way makes it clear whether a Massachusetts traveler is headed North (Portsmouth, NH) or South (Providence) while on a Massachusetts road.
posted by Jewel98 at 9:04 PM on January 2, 2014

But Pawtucket is the city bordering MA on I-95! We have several entire cities here!

I will miss this teeny tiny state....
posted by vsync at 10:50 AM on January 3, 2014

This totally screwed me up the first few times I drove in Germany - they don't use ANY cardinal directions on the signs, ONLY the next town. So if you don't know your German geography, only that you need to go east, you are SOL. Thank goodness for the poorly designed but at least barely functional Renault GPS!
posted by Mr. Big Business at 11:23 AM on January 3, 2014 [1 favorite]