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10 Things You Might Not Know About the U.S. Interstate System

Mental Floss logo Mental Floss 9/4/2015 Emily Becker
10 Things You Might Not Know About the U.S. Interstate System © istock 10 Things You Might Not Know About the U.S. Interstate System

Inspired by the network of high-speed roads he saw in Germany during World War II, Dwight D. Eisenhower championed the passing of the Federal-Aid Highway Act of 1956. The law funded the first 41,000 miles of paved glory that made up the early U.S. interstate system, which now boasts 46,876 miles and runs through all 50 states. (Yes, even Alaska and Hawaii.) Prepare for your next cross-country (or cross-town) road trip with the following facts.

1. IT TOOK 17 YEARS TO CREATE AND FUND THE IDEA OF THE INTERSTATE.

Two members of the U.S. Bureau of Public Roads presented a report to Congress in 1939 that detailed the need for a non-tolled road system in the U.S. The Federal Highway Act of 1944 allowed for development of a 40,000 mile National System of Interstate Highways, but it didn’t provide any method of funding, so it went nowhere. It wasn’t until the act of 1956 that funding was finally allocated to its construction.

2. PEOPLE FIRST LOVED, THEN HATED IT. 

When the Interstate Highway Act was passed, most Americans thought it was a good idea. But when construction started and people, especially in urban areas, were displaced and communities cut in half, some started to revolt. In the 1960s, activists stopped construction on highways in New York, Baltimore, Washington, D.C., and New Orleans, which resulted in several urban interstates becoming roads to nowhere.

3. EVERY STATE OWNS ITS PORTION (INCLUDING THE POTHOLES) …

A car travels over a pothole on February 24, 2014 in the Brooklyn borough of New York City. © Spencer Platt/Getty Images A car travels over a pothole on February 24, 2014 in the Brooklyn borough of New York City. This means the state is responsible for enforcing traffic laws and maintaining the section of highway in its borders. Currently, the “largest pothole in the country” award has been claimed by this section of I-75 outside Detroit. 

4. … EXCEPT FOR ONE (FORMER) BRIDGE.

The Woodrow Wilson Memorial Bridge (I-95/495) that crossed the Potomac River into Washington, D.C. used to be the only part of the interstate system owned by the Federal Highway Administration. But issues over it being too small led to the creation of a new, bigger, taller bridge. As for the old one? It was destroyed, in part by people who won a contest for having “the toughest daily drive.”

5. THE STATES SET THE SPEED LIMITS.

Speed limit sign by the road. © Image Source/Getty Images Speed limit sign by the road. However, in the early 1970s, all 50 states set their speed limits to 55 mph. A clause in the Emergency Highway Energy Conservation Act signed into law by Richard Nixon dictated that if a state did not set its highway speed limit to 55 mph, that state would lose its federal highway funding. 

6. THE SIGNS ARE TRADEMARKED.

The red, white, and blue shields used to designate interstate numbers are trademarked by the American Association of State Highway Officials. The original design for the shield was drawn by senior traffic engineer Richard Oliver of Texas and selected out of 100 entries in a national design competition in 1957.

7. INTERSTATES AND HIGHWAYS WITH THE SAME NUMBER CANNOT RUN THROUGH THE SAME STATE.

Road sign in Monument Valley Navajo Tribal Park. © Thinkstock/Getty Images Road sign in Monument Valley Navajo Tribal Park. The numbering system used for interstates is intended to be the mirror opposite of the U.S. highway system, so drivers won't be confused about whether to take Highway 70 or Interstate 70. For example, I-10 runs through southern states east-west (as all major even-numbered interstates do; odd-numbered interstates run north-south), while Highway 10 runs through northern states. Because I-50 would run through the same states as Route 50, the number will never be used.

8. I-99 DOESN'T FOLLOW THIS SYSTEM, BUT THAT'S NOT THE FEDERAL HIGHWAY ADMINISTRATION'S FAULT.

According to the Federal Highway Administration's numbering system, Pennsylvania's former US 220 should have been named something like I-876 or I-280. But Representative Bob Shuster wanted a catchier moniker for it. According to The New York Times, as a child he was fond of the No. 99 streetcar, which he used as his inspiration for the road's tag. 

9. THE INTERSTATE IS PART OF THE U.S.' ATOMIC ATTACK PLAN. 

A major concern during Eisenhower’s presidency was what the country would do in the event of a nuclear attack. One of the justifications for the building of the interstate system was its ability to evacuate citizens of major cities if necessary.

10. THERE ARE NO DESIGN RULES DICTATING THE SHAPE OF ROADS.

Lombard Street, the world's most crooked street, San Francisco, Calif. © Getty Images Lombard Street, the world's most crooked street, San Francisco, Calif. A major myth of the interstate system is that one out of every five miles is straight so an airplane can land. While this has happened, there are no rules or regulations that require such a design. Also, there are no requirements for curves to be designed into a highway to keep drivers awake. However, the Federal Highway Administration does admit that this is a perk of winding roads.

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