The Interstate System

History
There had long been a recognized need to have a national highway system in the United States. Although transcontinental roads existed before and during the early 20th century, they were inadequate for long distance travel. In 1919, a young Lt. Colonel named Dwight Eisenhower participated in a transcontinental US Army convoy from Washington, DC to San Francisco. The journey, much of it on unpaved and poorly signed roads, took 62 days. Though the adoption of the US highway system in 1925 brought some improvements to the road system, these improvements were inadequate, particularly outside urban areas for people traveling long distances.

During the second World War, Eisenhower noticed how easily German, and later Allied, forces in the region could move from place to place thanks to the Autobahn system of superhighways. This experience, combined with memories of the 1919 convoy, convinced Eisenhower of the need for a national system of limited access highways in the United States.

On June 29, 1956 under Eisenhower's administration, the Federal Highway Act created the system that we now formally call the "Dwight D. Eisenhower System of Interstate and Defense Highways." One of the problems with the US highway system was getting states (which often balked at the construction costs) to support the system. A national superhighway system was now viewed as a critical part of national defense, and as such the federal government would pay for 90% of the costs to construct the Interstates. On August 2, 1956, the first contract for Interstate construction was awarded by the state of Missouri for work on US-66 (now I-44).

Current Status
The Interstate system now consists of 45,012.52 miles of limited access roads built to some of the world's highest uniform design standards. These include 12 foot wide lanes and 10 foot wide shoulders, a design speed of at least 50-70 mph, at least two lanes in each direction, and no traffic lights or intersections (all cross traffic must be grade separated). All Interstates must also be limited access roads (owners of adjacent lands have no access rights; driveways cannot be built up to Interstates. Motorists must enter and leave Interstates only at designated interchanges)

The Interstate system is the backbone of the transportation system in the United States, carrying 21 percent of the nation's traffic on just 1 percent of the nation's roads. The importance of the system was demonstrated after the Sept. 11 terrorist attacks shut down all air traffic. During this time, the highways served as a vital link between states for long distance travel. Today, thanks to the Interstate system, it is now possible to travel from coast to coast by car in less than 50 hours.

Numbering Conventions
The numbering convention adopted for the Interstate system is as follows:

TWO DIGIT* ROUTES: These are primary Interstates. Anything that ends with the number 0 or 5 (multiples of 5) is a major Interstate. Major Interstates typically run all the way or a good part of the way across the country. For primary Interstates,
- Even numbered routes run west-east, with lower numbers farther south
- Odd number routes run north-south, with lower numbers farther west
Therefore, I-5 is the westernmost major north-south Interstate, running from Mexico to Canada through California, Oregon, and Washington. I-95, the easternmost major north-south route, runs through Florida, Georgia, South Carolina, Virginia, Washington DC, Maryland, Delaware, Pennsylvania, New Jersey, New York, Connecticut, Rhode Island, Massachusetts, New Hampshire, and Maine. Similarly, I-10 runs west-east along the Gulf coast, while I-90 goes close to the Canadian border.

*NOTE: Anything between 0 and 10 is considered two digits, although the leading "0" is omitted when these routes are signed.

THREE DIGIT ROUTES: These are spurs off the two digit routes, often built where a two digit route enters a metropolitan area. The last two digits denote the route from which the spur originated. Spurs must be connected either directly or recursively to the main "parent" route. Thus, a x80 spur must either must either connect to I-80, or to another x80 spur. There is a numbering convention for choosing the leading digit. In general,
- If x is even, the route is a spur around a metropolitan area (at the time of the route's adoption)
- If x is odd, the route is a spur into a metropolitan area (at the time of the route's adoption)

Cool Interstate Facts & Trivia
- THE LONGEST PRIMARY INTERSTATE is I-90, which runs 3,085.27 miles from Seattle to Boston. I-80 is the second longest, at 2,906.77 miles going from San Francisco to New York.

- THE LONGEST SPUR is I-476 in Pennsylvania, which runs 129.61 miles from I-81 northwest of Scranton to I-95 near Chester, southwest of Philadelphia.

- THE PENNSYLVANIA TURNPIKE (present day I-76) was the first limited access, divided highway in the U.S. The 260 km section between Irwin and Carlisle was the first section of freeway opened to the public on Oct. 1, 1940. The Turnpike's design was used as a model for the construction of much of the Interstate system

- TOLLS COLLECTION IS PROHIBITED on Interstate highways constructed with federal Interstate funds. Roads that were constructed first with state money and later signed as Interstates are exempt, however. This is why toll roads are much more common in the eastern states, which already had a highway system in place when the Interstate system was adopted.

- THERE ARE INTERSTATES IN HAWAII. All of them are on the island of Oahu and they're called H1, H2, and H3. Interstate H3 was completed just a few years ago. It was designed to minimize impact on the surrounding environment (the rainforests around the Ko'olau mountains) while offering great views for drivers. On each side of the Ko'olau mountains, it runs along twin viaducts as much as 100' high so it required as little removal of the forest as possible. In between, it goes through the mountains in a mile long tunnel. This is the only tunnel I've ever been in that curves left to right and changes elevation as it goes through the mountain. H3 is a high tech road. The tunnels are ventilated by fans, which are controlled by air sensors inside the tunnel. Also, a system of radars tracks the size and speed of each vehicle, so that if a vehicle stalls in the tunnel Hawaii DOT can remove it as quickly as possible.

- There is a section of I-5 between the Grapevine and the San Fernando valley where the northbound lanes are west of the southbound lanes. You can see traffic going in the other direction by looking to your right.
Photos of the points where the I-5 crosses over itself:
Southbound at northern crossing point
Southbound at southern crossing point
Northbound at southern crossing point

- I-180 in Cheyenne, Wyoming, has traffic lights and intersections on its mainline. Although federal funds were secured to build this expressway, a loophole in the bill did not require the Wyoming DOT to construct the road to Interstate standards to receive these funds.

- Alaska is the only state not served by the system. If there were Interstates in Alaska, they would be numbered A1, A2, etc.

Numbering Violations
There are a few cases where the Interstate numbering system is violated. Most of them are minor, and are simply the result of routes being rerouted. However, a couple of these are so outrageous they're worth pointing out.

I-238 (Hayward, CA) - This 2.1-mile connector between I-880 and I-580 is sometimes referred to as the "Orphan" Interstate because it has no parent route. There is no I-38, and even if there were, it would belong south of I-40 in Southern California, not anywhere near the Bay Area. At one time, this short section of freeway was signed as CA-238, but Caltrans and the federal government wanted to close a gap in the Interstate system, making it possible to go this short distance between I-880 and I-580 without leaving the Interstate system. The reason was probably that the Interstate shield is far more recognized than the California state highway shield, kinda like a brand name. Anyway, at the time, there were no x80 numbers available. I-180 and I-480 could not be used because 180 and 480 were California state highways and California doesn't allow duplication of route numbers. All other x80 combinations were taken by Interstates in the Bay Area, so 238 was allowed to keep its number. This is the only time in the history of the Interstates that this has happened. As weird as it is, I-238 does have some credibility because its numbering was approved by AASHTO.

I-99 (Bedford, PA to Bald Eagle, PA) - This has got to be my least favorite Interstate highway because it's the worst numbering violation in the entire system. To make matters worse, there isn't even a good reason for this one (as opposed to the situation with I-238). This road has the word "pork" written all over it. Back in 1995, the chairman of the House Transportation Committee (*cough* Bud Shuster *cough*) wanted an Interstate to serve the Bedford-Altoona corridor in his district, and got federal funds to upgrade US-220. Ok, that part's fine. Now here's where the mess starts. Not only did Mr. Shuster demand that the highway not be signed as a x76 spur (as it should have been), but he had the I-99 designation written into law! (No Interstate had ever had its designation written into law before). The numbering conventions state that I-99 should be a north-south highway east of I-97; I-99 isn't even east of I-81. Someone driving eastbound on the PA turnpike is going to wonder if he/she somehow passed I-95 and Philadelphia without knowing it. As if all that weren't enough, Shuster even got the highway named after him! Personally, I think this route should be simply renmbered as a spur from I-76. Shuster resigned from office in 2001 under pressure, but unfortunately his highway lives on.

Think I'm being too harsh? Check out these I-99 pages:
I-99 page at pahighways.com
I-99 at interstate-guide.com

I-93/I-95 (Boston, MA area) - In the immediate Boston metropolitan area, I-93 is actually east of I-95. This numbering violation is tame in comparison to the others, as these freeways are only 8-10 miles apart. I-95 was originally supposed to go through Boston, but was routed around it when one of the intended segments was never built.

Other random thoughts on the Interstate system
Al Gore, Sr., father of our former vice president, was one of the co-authors of the bill which created the Interstate system. Which makes me wonder if he'll claim to have invented Interstates the way his son claimed to have invented the Internet. Like father, like son?

<bad joke>It would be cool if I-86 ran into the Bay Area just north of I-80 and sent spurs down into Santa Clara County. That way, the Silicon Valley could claim an x86 based highway system =).</bad joke>


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