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| Scott Nazelrod |
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All you need to know to get started roadgeeking.
Most states have at least three (but perhaps more) different types of highway. Most people are familiar with at least the Interstates but refer to the other two classes as just Highway 77, or Route 62, or the 101 or whatever. Anyway, they are (in order of importance):
That's pretty much it in most states. Some states give you other levels; Missouri has a well-known system of "supplemental routes" signed by letters inside white squares [Missouri Supplemental Routes]. Several counties in the U.S. provide county routes, which are typically signed by blue pentagons with yellow numbers.
2006 marks the 50th anniversary of the Federal-Aid Highway Act of 1956. This is the law signed by President Dwight D. Eisenhower that created the Interstate Highway System, a high-speed network of roads designed to revolutionize our nation's way of getting around. And it has — travel from one end of the country to the other takes about one week now compared to about a month on the old (but still effective) U.S. Route system.
The Interstate system does this by consisting of high-grade freeways, which are roads that don't directly connect to any other roads; you can travel from a freeway to another road through a series of ramps connecting them. The whole set of ramps is usually referred to as an interchange. To be included into the system and assigned a number, a freeway has to meet stringent guidelines set by a group of highway engineers in all 50 state governments. Among these are rules which say interstates cannot have curbs (so cars can safely pull off the road in case of emergency), they must use interchanges rather than a direct intersection, and bridges have to be at least 16 feet high.
A common myth about the Interstate system is that one out of every five miles has to be straight, to allow planes to land. This is untrue. It was considered when the system was originally planned to build emergency runways next to interstates, having the freeway as an access road to the landing strip. However, it was realized this would cost too much, so it was never implemented. (The 1-mile-in-5 provision would not be possible in mountainous states like Colorado and West Virginia, and in New England where a large number of curves is often necessary to avoid preexisting buildings and geographical obstacles.)
An interesting provision was invented to determine the ways numbers are assigned to Interstates. First of all, most interstates have a number from 1 to 98. If the number is odd, the road runs north-and-south. And if a number is even, the interstate runs east-and-west. Major interstates, which often run across most of the country, end in 0 or 5. I-35 and I-40 are two major interstates that run through my state, Oklahoma.
What a lot of people don't know is that the numbers also identify where the highway is in the nation. The low-numbered highways lie along our south and west borders. Our lowest numbered interstate, I-4, cuts across the middle of Florida. Similarly, I-5 runs along the California coast up to Seattle. Then, as you move toward the opposite border, the numbers increase. Interstate 10 runs along the southern border of the United States, stretching from San Diego to Houston to New Orleans and Jacksonville, Florida — north of I-4. The next major interstate route east of I-35 is Interstate 45, running from Dallas to Houston. (Yes, that is all within Texas. Interstate refers to the system, not individual routes, though the majority of routes are in fact truly interstate.) I-95 is the highest-numbered major highway, running along the East Coast.
The planners decided that more freeways could be built to help cities out with local transportation. So, they planned these out as secondary interstates — these interstates have three digits and can range from 101-999. The last two numbers of these highway designations are the same as a primary interstate that the highway connects to. The Oklahoma version of I-240, for instance, connects to I-40 at its eastern end. (Numbers can be duplicated, hence the phrase Oklahoma version: see below.) The first digit lets us know what sort of highway we are referring to — a loop highway which connects to an interstate at both ends (like I-240 — it connects to I-40 on one end and I-44 on the other), or a spur highway which breaks out from its "parent" but doesn't reconnect to another interstate (like I-540 in Arkansas). Note that in secondary interstates, the last number doesn't matter — I-540 in Arkansas is completely north-south, but ends in an even number simply because its "parent" highway (I-40) runs east-west.
The terms primary and secondary interstate can be a bit obscure at times (and a bit too much to write), so many roadgeeks refer to them simply as 2dis and 3dis (for two digit and three digit interstate respectively). 2dis are two-digit (primary) interstates, while 3dis are three-digit (secondary) interstates.
Numbers are reused in many places. For instance, there are two I-76's, one in Colo./Neb. and another in Ohio/Penna. Also, 3di numbers are reused in a number of places - the only restriction is that there can only be one of each designation within a single state. (There are three I-240's, one in Oklahoma, one in Tennessee, and one in North Carolina.)
There are only two interstates in the system as of 2006 that seriously violate the system. (There are other, minor grid violations, like I-44 extending south of I-40 in southwest Oklahoma, and breaks in interstate standards, like roads connecting directly to the interstate instead of via an interchange. These are too minor and numerous that we won't cover them on this page.) These two highways are Interstate 99 in Pennsylvania, and Interstate 238 in the San Francisco, CA area.
I-238's problem is simply the fact that it doesn't connect to its "parent" highway, I-38. This would be okay by the rules if Interstate 38 existed. However, as of now, there is not an interstate numbered "38". Furthermore, even if 38 existed, it would be much farther south in order to comply to the grid.
So how did I-238 come about? The problem that led to the "238" number being picked is that at the time of the freeway's construction, there were no more Interstate spurs off I-80 available. It was suggested that I-180 be used, but Caltrans (the California road agency) rejected this number, as there was a State Route 180 in use around Fresno. Since the new freeway was designated as SR-238 before it was upgraded to an Interstate, it was allowed to keep the old number but become an interstate.Interstate 99 is the more problematic one. It was originally started as U.S. Highway 220, a two-lane road. It was upgraded to an Interstate through "pork-barrel" legislation written by Senator Bud Shuster from Pennsylvania. The number was also a provision of the pork bill. This angered many, as the "99" number grossly violated the numbering grid, falling between Interstates 79 and 81. What was even worse was that I-99 served a town with a very small population (Altoona, Pennsylvania) and was shorter than some 3dis, leading some to ask why it couldn't be left as U.S. 220. To add insult to injury, after Shuster's retirement, the highway was named after him.
The U.S. Route System is signed with white shields with black lettering. These were the original national numberered highways, and were introduced around 1926. A great many people remember its most famous - but alas, now defunct - highway, the venerable U.S. Route 66. The U.S. system has retained an aura of backwoodsy charm, though many people bypass them in favor of the more direct and safer Interstates.
The U.S. numbering system is similar to the Interstate system's, because it was the inspiration for the newer highways' numbering system. Rather than being along the south and west as on the Interstate system, the low routes on the U.S. system run along the east and north borders. That is, U.S. 1 runs along the east coast, and U.S. 101 along the west coast.
One major difference between the Interstate and U.S. systems is that the numbers for "major" route status are 0 and 1, rather than 0 and 5 as in the Interstate system (though "5" routes are still usually fairly important). Thus, U.S. 81 is a major highway. Spur routes are different in the U.S. route system as well; they are assigned sequentially*, and cannot be duplicated. They often cross multiple state lines unlike Interstate 3dis. (Note that U.S. 101 is not actually a spur route; it's actually a major highway ending in 1 rather than a spur of U.S. 1.)
*This actually led to an interesting situation with the sixth spur of Route 66. After U.S. 66 was decommissioned, the governor of New Mexico successfully got U.S. 666's name changed to U.S. 491.
There's quite a few U.S. route system violations:
In addition to these egregious violations, the U.S. route system contains many out-of-sequence highways, such as U.S. 6, which spends most of its length south of U.S. 20.
Most of the U.S. Route system's numbers have been assigned at one point or another. The only numbers that have not yet been assigned are 39, 47, 86, and 88. Many highways have been decommissioned, however, due to absorption by other U.S. routes or replacement by Interstates. Those that have been assigned in the past but are not currently assigned are 28, 32, 37, 38, 55, 66, 94, and 99.
As mentioned before, the U.S. route system is now secondary to the Interstate system in terms of national importance. This has led to the decommissioning of several highways. The most noticed deletion was that of U.S. 66 (obsoleted by Interstates 40, 44, and 55), followed by U.S. 99 (obsoleted by Interstate 5). Many other routes have been truncated (shortened) due to the Interstates. One particular case is U.S. 91, a former major route running from San Diego to Las Vegas to Montana. Due to the arrival of Interstate 15, U.S. 91 was truncated to only 120 miles through Utah and Idaho. In many cases, the U.S. route was upgraded to Interstate on-the-spot - the highway was dualized and interchanges added, and a new alignment only built where necessary.
Another reason the U.S. route system has shrunk has been AASHTO's increasingly strict interpretation of the numbering rules to not include single-state routes. Thus, short routes like U.S. 266 in Oklahoma have been on the downfall. In most cases, decommissioned U.S. routes are downgraded to state routes instead of being abandoned completely.