Guide signs
Interstate Route Marker sign
Identifies which interstate highway you are currently on. Odd numbers generally run north to south and even numbers generally run east to west.
- Trapezoid
- Blue
- MUTCD M1-1
Shape and background first
Federal designation M1-1 in the MUTCD, the national standard every state signs to. Posted at every interchange and repeated every few miles along the route so drivers can confirm they are still on the correct highway.
What the MUTCD specifies
Designation: M1-1
MUTCD Section 2D.11
Conventional road size: 24 x 24 in
Source: Federal Highway Administration, MUTCD 11th Edition (December 2023), Part 2, Table 2D-1, verified 2026-09-26.
What the test wants you to know
The mistake people make
Three digit interstates are the real exam trap: a number that starts with an even digit is usually a bypass or loop around a city, while one that starts with an odd digit is usually a spur that dead ends into downtown. Examiners test that pattern far more often than they test the shield itself.
