Guide & Services Road Sign (M1-1a)
3-Digit Interstate (Loop or Spur) Sign Meaning & Driving Rules
Identifies an auxiliary interstate route serving as a circumferential beltway around a city or a connector spur.
Required Driver Action & Right-of-Way Protocol
Recognize that even prefixes circle around the city while odd prefixes enter and terminate in the downtown core.
Detailed Overview & Purpose
3-Digit Interstate shields indicate branch routes connected to a primary two-digit interstate. The first digit tells you whether the road loops around a city or dead-ends:
If the FIRST digit is EVEN (e.g. I-285, I-495, I-610), the route is a loop or circumferential beltway that connects back to an interstate on both ends. If the FIRST digit is ODD (e.g. I-195, I-395, I-705), the route is a spur that branches off into a city or port and terminates.
Key Standard & Origin: Even first digit = Loop/Beltway (connects at both ends). Odd first digit = Spur (terminates at one end). The last two digits identify the parent highway.
Where You'll Find This Sign
Metropolitan freeway loops, bypasses, city center connectors, and airport expressways.
Common Driver Mistakes to Avoid
Assuming a 3-digit interstate continues cross-country; spurs terminate inside urban centers.
How This Sign Appears on the DMV Knowledge & Road Test
Essential highway navigation question: even 3-digit prefix vs. odd 3-digit prefix.
Legal Penalties and Moving Violations
None; guide sign.
When you encounter the official 3-Digit Interstate (Loop or Spur) (M1-1a) on a roadway, what is your legal duty?
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