Interstate Route Sign: Reading the Red and Blue Shield
The Interstate route sign is a shield with a red top band reading INTERSTATE and a white route number on blue. It identifies a highway of the national Interstate system, a network of freeways with no traffic signals or at-grade crossings. Odd numbers run north–south and even numbers run east–west, which helps you know your direction at a glance.
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Interstate sign quiz: 3 test-style questions
- An Interstate highway with an odd number, such as I-95, generally runs: East–west / North–south / In a loop around a city / Only inside one state. Answer: North–south. Odd-numbered Interstates run mainly north–south; even-numbered ones run mainly east–west.
- A three-digit Interstate such as I-495 whose first digit is even usually: Is a spur that ends in a city / Is a loop or bypass that reconnects to the main route / Is a toll road / Is closed to trucks. Answer: Is a loop or bypass that reconnects to the main route. As a general rule, an even first digit marks a loop or bypass that rejoins its parent route; an odd first digit marks a spur. There are exceptions.
- You miss your exit on an Interstate. What should you do? Back up on the shoulder to the exit / Stop and wait for a gap to reverse / Continue to the next exit and find your way back / Make a U-turn through the median. Answer: Continue to the next exit and find your way back. Never back up or turn around on a freeway. Take the next exit; median crossovers are for authorized and emergency vehicles only.
What the Interstate route sign means
The Interstate Route sign (MUTCD M1-1) is a shield-shaped route marker with a red band on top carrying the word INTERSTATE, and a blue field with the route number in white. It identifies a highway of the Dwight D. Eisenhower National System of Interstate and Defense Highways, built to freeway standards: controlled access via ramps, no traffic signals, no railroad crossings at grade, and opposite directions separated by a median.
Route markers are guide signs: they tell you where you are and where to go rather than giving an order or a warning. A green shield with the word BUSINESS marks an Interstate business loop or spur through a town center, which is a regular street, not a freeway. U.S. routes use a white shield with black numbers, and each state designs its own state-route marker.
How Interstate numbers work
- Odd numbers run north–south, lowest in the West (I-5 on the Pacific coast) and highest in the East (I-95 on the Atlantic coast).
- Even numbers run east–west, lowest in the South (I-10) and highest in the North (I-90, I-94).
- Three-digit routes are branches of the two-digit route in their last two digits. As a rule, an even first digit is a loop or bypass that reconnects; an odd first digit is a spur.
- Exit numbers in most states match the nearest mile marker, counted from the state's southern or western border. Exit 120 is about 120 miles from that border.
Driving on the Interstate
Enter using the on-ramp and acceleration lane, and yield to traffic already on the freeway (see the merge sign). Keep right except to pass; many states make this a law. Read the green guide signs well ahead so you can move into the correct lane early, and watch for EXIT ONLY lanes and left-side exits.
Never stop on the travel lanes, back up or turn around. If you miss an exit, take the next one. Use the shoulder only for emergencies, and move over for stopped emergency vehicles as every state's Move Over law requires.
Test traps
Sign colors are often tested: green guide signs give directions and distances, blue signs show motorist services such as the hospital sign, and brown signs point to parks and recreation. A question may also ask what you do if you enter an exit ramp by mistake: if you see WRONG WAY or DO NOT ENTER signs, stop and turn around safely before reaching the freeway.
Related signs
Freeway driving also involves the divided highway sign, the HOV lane sign and the exit and ramp advisory speeds. Review all categories in our road signs test guide.
Interstate sign FAQ
What do odd and even Interstate numbers mean?
Odd-numbered Interstates run mainly north–south, and even-numbered ones run mainly east–west. Numbers increase from west to east and from south to north.
What is the difference between I-495 and I-395?
Both are branches of I-95. As a general rule, an even first digit (495) marks a loop or bypass that reconnects to I-95, while an odd first digit (395) marks a spur. There are exceptions.
Why do exit numbers jump, like Exit 12 then Exit 18?
Most states number exits by the nearest mile marker, so the gap between numbers is roughly the distance in miles between exits.
What does a green Interstate shield mean?
A green shield marked BUSINESS identifies an Interstate business loop or spur, usually a regular street through a town's commercial area, not a freeway.
Official sources
- FHWA — Manual on Uniform Traffic Control Devices (MUTCD)
- FHWA — Interstate System: frequently asked questions
Keep studying
- Merge sign
- Hospital sign
- HOV lane sign
- Divided highway sign
- All U.S. road signs
- Practice tests by topic