Wednesday, May 20, 2015

The US interstate freeways, a bit of trivia I found interesting

In 1956, when ground was broken, it was the largest public works project in the history of the world: with 41,000 miles and 50,000 bridges. There are now 46,876 miles, and 2,900 miles of turnpikes

Who numbered the Interstates?

The officials involved with the creation, decided that they would apply numbers to the Interstate System as they had did to the U.S. numbered highways.

But mirror image, that is, opposite sides of the country from the highways with the same numbers
(for example, U.S. 1 is on the East Coast, while I-5 is on the West Coast; U.S. 10 is in the north while I-10 is in the south).

The Interstate numbering plan was based on the plan used to number the U.S. numbered highways, so in both plans, numbers ending in zero are used for transcontinental and other major multi-State routes.

Why isn't there a I-50?
 However, one of the rules for Interstate numbering is that numbers are not duplicated on Interstate highways and U.S. numbered routes in the same State.

Duplicate numbers would be confusing for motorists; for example, if told to take "Route 50," the motorist might follow the wrong one. Because the Interstate numbering plan is a mirror image of the U.S. numbered highway plan, I-50 would be located in some of the same States as U.S. 50 (Ocean City, Maryland, to Sacramento, California). Therefore, "50" has not been used for an Interstate route.

So... who screwed up a perfectly good system? Congress. Seriously.
Although State and Federal officials normally select Interstate route numbers, Congress made the choice of "99" for upgraded U.S. 220 in Pennsylvania.

Also I 35W and I 35E are allowed in Texas because the American Association of State Highway Officials let them http://www.atlasobscura.com/articles/tedium-syndication-highways

Why the difference in overpass heights from 12 to 16 feet?
After the Soviet Union launched its Sputnik satellite in October 1957, the DOD determined that a 17-foot vertical clearance was needed for some larger equipment, such as the Atlas intercontinental ballistic missile, that could not be transported by rail.

 On January 27, 1960, the BPR issued instructions to its field offices changing the minimum standard to 16 feet for Interstate highways in rural areas.  All projects under design or construction were to be revised according to the new standard. The first construction project affected by the change was in Michigan, where highway officials using hydraulic jacks lifted the Clear Lake Road overpass on I-94 near Lansing from a clearance of 14-feet, 6-inches to 16-feet, 3-inches.

http://www.fhwa.dot.gov/interstate/faq.cfm#question14


Image from https://www.facebook.com/pages/Old-Cars/204098692935609

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