Interstate Highway Features and Reference Guides
There are set rules for the Interstate numbering convention, such as even numbers run west to east, and odds numbers are orientated from south to north. Branch routes are generally even numbers for loops and connectors, and odd numbers for spurs. Over the course of the Interstate Highway System history, the numbering rules were strictly enforced, but have become more lax over time with additions and extensions of existing routes. Interstate design standards remain, and any new route must adhere to these, with adequate shoulders, minimum lane widths and limited access standards. Proposed Interstate Highways cannot be formally added to the system until such upgrades are completed.
While there is no Interstate 38, I-238 exists in California, yet Interstate 50 does not? Interstate-Guide answers some of those questions and other Interstate trivia.
Interstate Guide's reference section explores the Interstate Highway System beyond individual routes, including numbering conventions, engineering standards, historical milestones, and lesser-known facts about America's most recognizable highway network.
Numbering Guide
Understanding primary, auxiliary, suffixed, and special Interstate designations.
Design Standards
How Interstate highways are engineered, signed, and built.
Trivia & Records
Shortest routes, longest routes, unusual numbering quirks, and system superlatives.
History
The evolution of the Interstate System from its origins through modern expansion.
Frequently Asked Questions
Answers to common questions about Interstate highways and their operation
Proposals & Unbuilt Corridors
Planned, speculative, and never-completed Interstate concepts from past decades.
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