Why the Interstate System Skipped I-50 and I-60
The absence of Interstate 50 and 60 from the US interstate system is more than just a numerical quirk. It's a strategic design choice that reflects the system's evolution and the need to coexist with existing highways. Let's delve into the reasons behind these omissions and the broader implications for the interstate network.
A Logical Numbering System with a Twist
At the outset, the interstate system's numbering was not arbitrary. It borrowed from the existing US highway system, which already had a one- and two-digit numbering scheme for long-distance routes. Routes running north-south were assigned odd numbers, while east-west routes got even numbers. This made sense, as it allowed for a scalable, nationwide network that could coexist with existing highways.
Numbers ending in zero or five were reserved for nationally significant routes, ensuring drivers could easily identify key routes. However, this also meant fewer available numbers for other routes, raising the question: why weren't I-50 and I-60 assigned?
Avoiding Duplication and Confusion
One key reason is to prevent duplication and confusion. Interstate numbers needed to be unique within each state. Interstate 50, for instance, would have overlapped significantly with existing US Route 50, which runs from the east coast to California. Using the same number for both roads in the same state would have caused confusion, undermining the very purpose of the numbering system.
Similarly, Interstate 60 would have overlapped with the well-established US Route 60, an east-west highway. The planners aimed to integrate the interstate system with the existing network, not overwrite it. By skipping these numbers, they avoided renaming or displacing existing routes, even though some of those old highways are now lost.
Beyond the Missing Numbers
The absence of I-50 and I-60 is just one symptom of the interstate system's design. Other inconsistencies remain, such as interstate numbers repeating in different parts of the country or appearing far out of geographic sequence (like I-99). These outcomes reflect political decisions and practical limitations that emerged as the system evolved. Once routes were built, renumbering them for aesthetic reasons offered little benefit to drivers.
The Bottom Line
The interstate system prioritizes ease of movement and national connectivity over numerical neatness. As long as motorists can understand direction and connection at a glance, the system is serving its purpose. The omissions of I-50 and I-60 are a testament to the system's thoughtful design, aiming to avoid confusion and duplication while integrating with existing infrastructure.
