Daily Archives: February 10, 2014

Why Are Highways Numbered to Satisfy Road Geeks?

In the US, we generally sign three different kinds of numbered highways: interstates, US routes, and state routes. In some states, there are also signed numbered county routes, but we’ll ignore them for now.

The numbering schemes for interstates and US routes (generally) follow some basic rules:

  • Two-digit routes are main routes (one-digit routes are understood to be included here).
  • Odd numbered two-digit routes go north-south.
  • Even numbered two-digit routes go east-west.
  • Interstate numbers increase south to north and west to east.
  • US route numbers increase north to south and east to west.
  • Three-digit routes are of the form “xPP”, and are supposed to connect to their “parent” two-digit route “PP” somehow, e.g. US-119 is supposed to connect to US-19.
  • Furthermore, the “x” for three-digit interstate routes is supposed to be an odd number if the route is a spur that connects to the parent only at one end, and even if the route is a loop that connects to the parents at both ends. For example, the I-405 freeway connects to the I-5 freeway at both ends, while the I-710 freeway only connects to the I-10 freeway at one end. . . sort of.
  • Two-digit numbers are almost never used in more than one place. Three-digit numbers are reused.

That’s all well and great. . . if you’re trying to make road geeks happy. In fact, road geeks get angry about routes that do not follow the numbering system; see the fury drawn by I-99 and the US-4xx routes if you don’t believe me.

Problem is, satisfying road geeks is a pretty strange goal for your highway numbering scheme. The purpose of building highways, as I understand it, is to facilitate the movement of people and goods. Highway numbering should promote that purpose. No one is out there driving around aimlessly looking for the 5, and, upon finding the 405, feeling relief that the 405 must take them to the 5. Actually, thanks to some rule-bending, a person depending on the numbering scheme would find themselves hopelessly lost in many places; consider, for example, that the 278 in New York doesn’t connect to the 78 anywhere. . . it doesn’t even come close.

Worse than that, in some parts of the country, the insistence on trying to follow the scheme makes things more confusing. The two prime examples of this have to be the Bay Area, which has only one two-digit interstate (the 80) and is therefore drowning in a sea of x80’s (the 280, the 380, the now-defunct 480, the 580, the 680, the 780, the 880, and the 980) and the Hampton, VA area (the 64, the 164, the 264, the 464, the 564, and the 664). When you roll up the 101 into San Jose, do you benefit from having to choose between the 280, the 680, and the 880? Of course not. Some states have implicitly admitted this; see, for example, that Maryland doesn’t sign the 595, realizing that the DC/Baltimore area, and the Northeast Corridor in general, already has plenty of x95’s.

So what would a logical highway numbering system look like? Well, the first thing it should do is communicate the quality of the road to you using the route shield. We have that a little bit with interstates – when you see the red and blue shield, you know you’re getting a freeway. But, in the same way that not all rectangles are squares, not all freeways are interstates.


So, any limited access facility should get the interstate shield. In the sign display shown above, the 5, the 101, and the 60 are all the same quality of road. They are all completely controlled-access freeways. The 39, which is implied to be just as good as the 60 by its route shield, is just a regular surface road.


Ahh, much better! You’ll note that I didn’t bother to change the 101 and the 60 to follow the interstate numbering scheme, even though there are numbers available (the 60 could be the 410, the 610, or the 810, and the 101 could be the 705). That’s because the interstate numbering scheme is pointless. There’s no logical reason that numbers have to increase south to north and west to east, and there’s no logical reason to not reuse numbers if they’re separated by a large distance. The 57 freeway should just become the I-57 freeway. No one is going to get confused and think they are in Cairo, IL instead of Orange County.

That takes care of freeways, which should all get the interstate shield, and state routes, which should be normal arterial roads. What about US routes? They should be used for major cross country routes that aren’t freeways. The current scheme basically allows the use of the US route shield if the route crosses a state line, which leads to the ridiculous scenario where the 199, at 80 miles long and serving the middle of nowhere in California and Oregon, is worthy of a US route shield, while the 99, which is over 400 miles long, is mostly freeway, and serves Chico, Sacramento, Stockton, Modesto, Fresno, Manteca, Bakersfield, and LA (almost) isn’t. The 199 probably does not deserve to be a US route. The 99 does.

Really, a lot of the 99 should be an interstate. The parts that are a freeway should use the interstate shield. The parts that aren’t should use the US shield. There’s no reason that one consistently numbered route has to use the same shield the whole way. Using different shields would help drivers understand that, say, the Angeles Crest Highway and the Glendale Freeway aren’t the same kind of road, even though they’re both part of the 2.


Nothing wrong with that signage.

There is another legitimate reason to do this: it takes godlike transportation power away from highway geeks (AASHTO) and faceless, unaccountable hacks (Congress). The interstate shield, because it symbolizes quality roadway transportation, carries a lot of weight, and states are willing to spend money to get it. That allows AASHTO and Congress to have discriminatory power to force some states to spend money for no good reason. Anyone want to make the case that it is really critical that Caltrans upgrade a few ramps on the 210 in San Bernardino before they’re allowed to throw up the interstate shield? Especially in light of comparison to laughably deficient legacy freeways like the 278 in New York and the 70 in Pennsylvania?

Granted, this isn’t a huge issue. We’ve got better things to worry about and spend money on. But as signage is replaced over time, we should move to this kind of system.

All sign images generated with Kurumi’s sign maker app.