US Route 138 runs along a northeast-southwest diagonal, mainly in northeastern Colorado. The route follows alongside the northeastern half of Interstate 76. For context, Interstate 76 runs northeast from Denver to the northeastern corner of Colorado, where it climbs across the state line into Nebraska for a minuscule distance, just to end at Interstate 80. While the portion of Interstate 76 southwest of Sterling is buddies with US Route 6, the portion northeast of Sterling is accompanied by US Route 138. At Sterling, US Route 6 bails to go eastward, so some US Route had to do Interstate 76's job before the days of the Interstates!  US Route 138 did that job, and yes, it does end in "38", even though US Route 38 doesn't even exist!  The portion of US Route 6 passing through Sterling, Colorado, was once labeled as "US Route 38," and US Route 138 was named after US Route 38 when it came about.  US Route 38 was gobbled up by an extension of US Route 6, but US Route 138 was allowed to continue on without any changes to its number.  That is why US Route 138 has the peculiar number it has.  US Route 138 begins at what is now US Route 6, in Sterling, and it runs northeastward, parallel with Interstate 76. As Interstate 76 ends at Interstate 80 near Big Springs, Nebraska, US Route 138 also ends at the US Route serving as a historical counterpart to Interstate 80, which is US Route 30. Though Interstate 76 is cut short from reaching the latitude of Big Springs, US Route 138 runs right into town, turning north to end at US Route 30.  US Route 138 runs through rather flat, dry, desolate areas of the high plains, in the rain shadow of the Rocky Mountains.

My photo of US Route 138 comes from Sterling, Colorado, a few blocks north of its southern point of beginning at US Route 6. This guide marker shows northbound travelers that the route is about to bend to the right at this intersection. This photo was taken during the trip to New Mexico in October 2024.

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