Section 5: Interstate Highway Numbering
Original Numbering System
The original numbering system for interstate highways established
that:
- north-south routes end in 5, beginning with 5 on the west coast and increasing on routes east of IH-5
- east-west routes end in zero, beginning with 10 in the south and increasing on routes north of IH-10.
Current Numbering System
After the initial interstate routes were designated, additional
corridors became eligible for interstate highway funding. Since
the initial routes had used all the available numbers ending with
“0” and “5,” an alternate numbering system was developed using even
and odd numbers, as follows:
- Odd numbers designate routes that generally run in a north-south direction.
- Even numbers designate routes that generally run in an east-west direction.
The number selected would generally fall in the normal sequence
between two existing interstate routes. For example, IH-27 is located
between IH-25 (New Mexico, Colorado, Wyoming, etc.) and IH-35 (Texas,
Oklahoma, Kansas, etc.).
Loops
Interstate loops use three digits; the first digit is an even number, while the last two digits are associated with the interstate highway that carries the major traffic stream.
Business Loops.
Interstate business loops typically retain the number of the interstate highway traversing the city or town and use a green route sign.Interstate Loops in Texas.
Texas interstate loops (both existing and possible) are as follows:Loop Number | Location |
|---|---|
IH 210 | El Paso (possible) |
IH 235 | Austin (possible) |
IH 410 | San Antonio |
IH 435 | Waco (possible) |
IH 610 | Houston |
IH 635 | Dallas |
IH 810 | Beaumont (possible) |
IH 820 | Fort Worth |