Though its signs indicate New York State Route Route 878, this road is actually part of the Interstate Highway System, as it was constructed using those funds. At just 0.7 miles long, it’s the shortest of any interstate highway route. The thoroughfare, which overlays the Nassau Expressway in Queens, is located between I-678 and the John F. Kennedy Expressway.

Jefferson City, Missouri, is one of four state capitals not served by the Interstate Highway System. The other three are Juneau, Alaska; Dover, Delaware; and Pierre, South Dakota. While all those states do feature portions of interstate highway somewhere within the state’s borders, none of those roads make their way through the capital cities.

At just 17.57 miles in length, I-97 — connecting the Maryland cities of Baltimore and Annapolis — is the shortest two-digit interstate route. Next on the list is I-99, which is 53.00 miles long and connects Bedford and Bald Eagle, Pennsylvania (that route is expected to be expanded in the future).

One of Eisenhower’s motivations to build the interstate system in the 1950s was the Cold War-era fear of atomic bomb raids. The President wanted to ensure that every American would easily be able to evacuate their location quickly if necessary, so the interstate system was officially named the National System of Interstate and Defense Highways.

Interstate 99, which connects Pennsylvania and New York, was almost called Interstate 876 or Interstate 280 because it connects Interstates 76 and 80. But former Pennsylvania Representative Bud Shuster, who helped secure financing, wanted something catchier, so he gave the interstate the number 99, named after a trolley from his hometown of Glassport, Pennsylvania.

When numbers for the interstates were determined, they were designed to be a mirror image of the numbers for state highways. So, for example, I-5 would be on the West Coast to differentiate from the existing Highway 5 on the East Coast. But because I-50 would fall in the middle of the country, it would lead to confusion with the existing Highway 50, so the number isn’t used.

There are 29 Interstate Highway routes in New York, the most of any state. Behind New York is California, with 25 routes. Texas is home to the longest length of interstate highways, at 3,233.45 miles. The runner up on that front is also California, with 2,455.74 miles of interstate highways.

No point on the Interstate Highway System reaches a lower altitude than the Fort McHenry Tunnel. The tunnel, where I-95 crosses Baltimore Harbor, descends 107 feet below sea level. The lowest altitude point on land can be found on I-8 near the town of Seeley, California, which reaches 52 feet below sea level.

In 1956, the American Association of State Highway Officials wanted signs designed for the upcoming interstate system that would distinguish it from other highways, so they launched a competition asking each state to submit a design. Out of the 76 designs, a shield design by Texas traffic engineer Richard Oliver won. That emblem still appears on the signs today.

When interstates were first introduced, they were mostly popular, but by the 1960s, some citizens began to despair at the destruction they caused and communities they displaced. Activists began protesting interstate construction and actually prevented it in Baltimore, New Orleans, and more cities, leading to abrupt ends to certain interstates. Activists dubbed these “roads to nowhere.”

Not all interstate highway speed limits are created equal. South Dakota has the highest average interstate speed limits — all interstate highways in the state, both rural and urban, have an 80 mph limit. Other roads in the state have a 70 mph limit. South Dakota also has the highest speed limits of any state overall.

Under the Federal-Aid Highway Act of 1956, a portion of U.S. 40 in Missouri became the first future interstate to utilize federal funds in its construction. That road was later designated the I-70 Mark Twain Expressway. The first paving to occur under this new act occurred on a separate portion of U.S. 40 (later I-70) located in Kansas.

When Eisenhower signed the Federal-Aid Highway Act on June 29, 1956, it created a 41,000-mile system of highways across the country. A bill passed nearly a decade prior in 1944 authorized the construction of all the highways (up to 40,000 miles), but didn’t include any way to pay for it. The 1956 law added another thousand miles to the allowed construction, and funded the project with $26 billion.

I-5 — which traverses through California, Oregon, and Washington — is the only continuous interstate highway to border both Mexico and Canada. It connects Tijuana, Mexico, with the Canadian province of British Columbua. The road runs parallel to U.S. Route 99 and travels through major cities such as Seattle, Portland, and Los Angeles.

Despite being an island with no connection to any other state, Puerto Rico is home to an extension of America’s Interstate Highway System. This is true of the non-contiguous states of Hawaii and Alaska, too. In these instances, the word “interstate” has less to do with connecting multiple states and more to do with the fact that federal government funding was used for the roads.

I-95 is the longest north-south highway in the Interstate Highway System, covering a distance of approximately 1,920 miles. The road begins in Moulton, Maine, with its terminus in Miami, Florida — crossing through a total of 16 states. The final portion of the road runs parallel to the Atlantic Ocean before finally reaching the southern tip of Florida.

Located an hour west of Denver in the Rocky Mountains, the Eisenhower Tunnel reaches a peak of 11,158 feet above sea level, making it the highest point in the Interstate Highway System. Upon its completion in 1979, the project became the highest-elevation tunnel in the world, though it has since been surpassed by Tibet’s 16,000-foot-high Fenguoshan Tunnel.

Every interstate has a number, and that number determines the direction the highway runs. Interstates ending in even numbers, such as I-94 or I-20, run east to west. Interstates ending in odd numbers, like I-5 and I-65, run north to south. The lowest numbered north-south highways start in the west, and the lowest numbered east-west highways start in the south.

When President Dwight D. Eisenhower developed the idea for the interstate highway system, he had three different inspirations. First, he participated in the U.S. Army’s First Transcontinental Motor Convoy in 1919, which showed him structural challenges in the nation’s roadways. Second, he saw how efficient the Autobahn highway was when he visited Germany. And third, he was worried about evacuation routes if a bomb went off.

The longest interstate in the country is its northernmost one, I-90, which runs for 3,085 miles between Seattle and Boston and passes through 13 states. The interstate wasn’t fully completed until 1993, when the Lacey V. Murrow Bridge connected Seattle to its eastern suburbs. The country’s second-longest interstate isn’t far behind; I-80 runs for 2,906 miles from San Francisco, California, to Teaneck, New Jersey.