The third US highway serving Denver was US 285, but it was not the same as the route that carries that designation today. Instead of heading west and south from Denver, the original US 285 went north from Denver, essentially following the route of modern US 287 through Broomfield, Lafayette, Longmont, Loveland, and Ft. Collins, ending in Laramie WY. Although US 285 [i] lasted only about eight years, it had various routings through downtown Denver, and multiple termini, all of which are discussed at length on the US 285 page. Also, please note: in order to more easily visualize all of the historic US highway routings in the Denver area, each of them have been overlaid on this interactive map.
US 40 will not be discussed much on this page... not because it is unimportant, but simply because of the remarkable fact that its routing through Denver has never changed! US 40 still follows Colfax all the way through the city: exactly the same route as it did when it was first commissioned over 90 years ago. I-70 across the Denver metro area was completed in about 1968. At any time since then, the Colorado DoT could have directed US 40 traffic to use I-70 instead of Colfax. Nearly all other US routes in Denver have been moved off surface roads and onto the nearest freeway, but for some reason CDoT has never done that with US 40.
Heading south from what is now Commerce City, US 85 originally followed the road currently designated as state highway 265. That is, southwest on Brighton Boulevard to Riverside Cemetery, where it makes a sharp turn and passes underneath a railroad by way of a very narrow tunnel. Continuing on from there, the SH 265 designation ends at its junction with I-70, but US 85 continued further southwest on Brighton Blvd, all the way to the point where it curves due south and becomes Broadway. Today Broadway is one-way southbound, but historically it carried both north and south traffic. This photo was taken looking north on Broadway at Walnut Street, at the south beginning of the viaduct:
(Incidentally, SH 185 was a highway that began by heading north from Brighton Blvd via 38th Street, which curves to become Washington Street; that was the highway that eventually became I-25.) Heading south from the Broadway viaduct, US 85's junction with US 40 (and probably US 285 as well) was right at the State Capitol. From Colfax, US 85 continued south on Broadway for another 2.5 miles. At Iowa Avenue, US 85 turned west to pass underneath a railroad, before turning south again on its present route (Santa Fe Drive).
Another change illustrated on the map above was the US 87 designation, which was rerouted in Wyoming and extended south into Colorado. It came into Ft. Collins and replaced the original US 285 all the way down to Denver (the remaining segment of former US 285 between Ft. Collins and Laramie became part of the new US 287 designation). From downtown Denver, instead of following Park Avenue southeast all the way to Colfax (as US 285 had done), US 87 joined with US 85 by turning south on Broadway, and those routes were twinned out of town (and actually all the way through the rest of Colorado, finally diverging at Raton NM). However, maps from just a little later (approx. 1938-1941) showed US 87 using an even older US 285 routing to get to Broadway, specifically 33rd Av - 20th St:
...because it was taken during the very brief timeframe when it was signposted as US 87 (enlarged here):
In 1937 (one year after US 87 was extended through Denver, and US 285 was changed) two additional US highways were routed into the city. The US 6 designation (which had previously ended in Greeley) was truncated at Wiggins and instead extended southwest through Denver (and through the remainder of Colorado, all the way to Long Beach CA). US 6 came into Commerce City heading southwest on the road that is now designated SH 2. Traffic was then directed south on Vasquez Boulevard, then south on Colorado Boulevard to Colfax. Initially US 6 was not routed along 6th Avenue (as it is today), nor did it go through Clear Creek Canyon west of Golden. Rather, US 6 was twinned with US 40 from the intersection of Colorado and Colfax west all the way to Empire Jct. (a distance of about 43 miles). Following are a few historic photos with signs marking the US 6-40 overlap, each of them from somewhere along the Colfax viaduct. This first one was taken looking west, possibly at the east beginning of the viaduct:
This next photo was also looking west along Colfax. I believe the photographer was standing at the southwest end of the Larimer viaduct:
For a brief time, the road that is now designated I-25 was complete both to the north and to the south from Denver, but not through the central part of the city. It was during this time that the US 87 designation was removed from its pairings with US 85 to the south and US 287 to the north, and instead applied to the new road. The separate freeway segments of US 87 were temporarily connected via Fox St - Park Av - Colfax Av - Colorado Blvd:
The I-25 designation was not officially applied to the Valley Highway until about 1962, and even then it may not have been signed as such immediately.
That map also illustrates that the US 285 designation had been removed from the Morrison Road corridor. Traffic was instead directed around Denver via a sort of beltway that consisted of Hampden Avenue and Havana Street, to a new terminus at Colfax (US 36-40-287).
The winter edition of the 1970 map was the first to show I-270 complete between I-70 and what is now I-76 (but at the time was still designated as I-80S). The 1970 summer edition was the first to show that US 36 had been redirected off of Colfax and onto I-70 / I-270 / I-80S / I-25 to the Boulder Turnpike:
In 1978, US 285 attained its current configuration when it was truncated to its interchange with I-25. This may have been done because I-225 had recently been completed, and since Denver now had a freeway bypass around the south and east sides, perhaps US 285's surface-level beltway was deemed obsolete. The former US 285 from I-25 up Havana to 6th Av became an extension of the SH 30 designation, while the one-mile segment from 6th to Colfax was removed from the state highway system:
Around the turn of the century, construction began on a project that would extend I-270 across I-76, allowing it to directly connect with I-25 and the Boulder Turnpike. The westbound connection was completed in 2000, and three years later the eastbound connection was opened to traffic. This removed all US 36 traffic from I-76 and I-25, allowing it to remain on I-270 between the Turnpike and I-70. In this way US 36 attained its current configuration...
...although it should be noted that this is an implied routing, because US 36 is not signed anywhere along its 42-mile concurrency with interstates 70-270 (between Denver and Byers). In the 1990s or 2000s, I vaguely recall a sign on eastbound I-70 directing US 36 traffic to use I-270, but as of 2017 no such signage remains.
In fact, several US routes in the Denver area now follow implied routings. That is because at some point CDoT made it their policy not to sign US routes along interstate overlaps. This was probably an attempt to reduce sign clutter, minimize expenses, and/or simplify inventory. But one major drawback is that, besides US 36, there are three additional US routes (US 6, US 85, and US 87) for which it is no longer possible to rely on directional signage to navigate through the Denver area.
That remained standing until August 2012; since then there is no signed evidence of US 87 in Colorado.
US 6 and US 85 are both signposted in the Denver area, but not where they are concurrent with I-25, and not at the exchanges between I-25 and I-70. Interestingly, as of 2017, there were still three assemblies on I-70 indicating the US 6-85 overlap. But they are kind of pointless, because for traffic heading south on Vasquez (US 6-85), drivers are not told that those routes continue to the west on I-70. Also, for traffic heading north on Santa Fe (US 85) or east on the 6th Ave. Freeway (US 6), there is no signage informing drivers that those routes continue to the north along I-25. CDoT certainly does not make it easy for travelers to follow US routes through the state.
Research and/or photo credits: Mike Ballard; Matt Salek; Dale Sanderson; Michael Summa