American Association of State Highway and Transportation Officials in the context of "Interstate Highway standards"

The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these highways were coordinated among the states, they are sometimes called Federal Highways, but the roadways were built and have always been maintained by state or local governments since their initial designation in 1926.

The route numbers and locations are coordinated by the American Association of State Highway and Transportation Officials (AASHTO). The only federal involvement in AASHTO is a nonvoting seat for the United States Department of Transportation. Generally, most north-to-south highways are odd-numbered, with the lowest numbers in the east and the highest in the west, while east-to-west highways are typically even-numbered, with the lowest numbers in the north, and the highest in the south, though the grid guidelines are not rigidly followed, and many exceptions exist. Major north–south routes generally have numbers ending in "1", while major east–west routes usually have numbers ending in "0". Three-digit numbered highways are generally spur routes of parent highways; for example, U.S. Route 421 (US 421) is a spur off US 21. Some divided routes, such as US 19E/US 19W and US 25E/US 25W, exist to provide two alignments for one route. Special routes, which can be labeled as alternate, bypass or business, depending on the intended use, provide a parallel routing to the mainline U.S. Highway—an example being US 74 and its many special routes.

Interstate 35E (I-35E), a north–south Interstate Highway, is the eastern half of I-35, where it splits to serve the Dallas–Fort Worth metropolitan area. I-35 splits into two branch routes, I-35W and I-35E, at Hillsboro. I-35E travels north for 97 miles (156 km), maintaining I-35's sequence of exit numbers. It travels through Dallas before rejoining with I-35W to reform I-35 in Denton.

During the early years of the Interstate Highway System, branching Interstates with directional suffixes, such as N, S, E, and W, were common nationwide. On every other Interstate nationwide, these directional suffixes have been phased out by redesignating the suffixed route numbers with a loop or spur route number designation (such as I-270 in Maryland, which was once I-70S) or, in some cases, were assigned a different route number (such as I-76, which was once I-80S). In the case of I-35 in the Dallas–Fort Worth area, since neither branch is clearly the main route and both branches return to a unified Interstate beyond the cities of Dallas and Fort Worth, the American Association of State Highway and Transportation Officials has allowed the suffixes of E and W in Texas to remain to the present day. I-35 also splits into I-35E and I-35W in Minneapolis–St. Paul, Minnesota, for similar reasons as the I-35 split in the Dallas–Fort Worth area.

Some U.S. Routes are given directional suffixes to indicate a split of the main route — for instance, U.S. Route 25 (US 25) splits into US 25E (east) and US 25W (west) between Newport, Tennessee, and North Corbin, Kentucky, and US 9W is an alternate of U.S. Route 9 between Fort Lee, New Jersey, and Albany, New York. These splits were in the U.S. Highway system from the beginning, and were used when two roughly-equivalent routes existed. The American Association of State Highway and Transportation Officials (AASHTO) no longer assigns these numbers, and, in theory, current ones are to be eliminated "as rapidly as the State Highway Department and the Standing Committee on Highways can reach agreement". This policy was adopted by 1996; however, many of these routes still exist, mostly in Tennessee.

Interstate 35E (I-35E) is an Interstate Highway in the US state of Minnesota, passing through downtown Saint Paul. It is one of two through routes for I-35 through the Twin Cities of Minneapolis and Saint Paul, the other being I-35W through Minneapolis. Thus, both ends of I-35E are shared with I-35W and I-35.

During the early years of the Interstate Highway System, branching Interstates with directional suffixes, such as N, S, E, and W, were common nationwide. On every other Interstate nationwide, these directional suffixes have been phased out by redesignating the suffixed route numbers with a loop or spur route number designation (such as I-270 in Maryland, which was once I-70S) or, in some cases, were assigned a different route number (such as I-76, which was once I-80S). In the case of I-35 in the Twin Cities area, since neither branch is clearly the main route and both branches return to a unified Interstate beyond the cities of Minneapolis and Saint Paul, officials at the American Association of State Highway and Transportation Officials (AASHTO) have allowed the suffixes of E and W in Minnesota to remain in the present day. I-35 also splits into I-35E and I-35W in Dallas–Fort Worth, Texas, for similar reasons as the I-35 split in the Minneapolis–Saint Paul area.

Interstate 35W (I-35W), a north–south Interstate Highway, is the western half of I-35 where it splits to serve the Dallas–Fort Worth metropolitan area. I-35 splits into two branch routes, I-35W and I-35E, at Hillsboro. I-35W runs north for 85.2 miles (137.1 km), carrying its own separate sequence of exit numbers. It runs through Fort Worth before rejoining with I-35E to reform I-35 in Denton. It is the more direct route for long-distance expressway traffic, as is noted on signs on I-35 leading into the I-35W/I-35E splits. During the 1970s, billboards existed on I-35 encouraging travelers to take the faster and shorter I-35W route.

During the early years of the Interstate Highway System, branching Interstates with directional suffixes, such as N, S, E, and W, were common nationwide. On every other Interstate nationwide, these directional suffixes have been phased out by redesignating the suffixed route numbers with a loop or spur route number designation (such as I-270 in Maryland, which was once I-70S) or, in some cases, were assigned a different route number (such as I-76, which was once I-80S). In the case of I-35 in the Dallas–Fort Worth area, since neither branch is clearly the main route and both branches return to a unified Interstate beyond the cities of Dallas and Fort Worth, officials at the American Association of State Highway and Transportation Officials (AASHTO) have allowed the suffixes of E and W in Texas to remain in the present day. I-35 also splits into I-35E and I-35W in Minneapolis–Saint Paul, Minnesota, for similar reasons as the I-35 split in the Dallas–Fort Worth area.