Interstate 270 angles northwest from I-70 by the Stapleton community in Denver through Commerce City to I-25 by a commerce park area at Welby in southern Adams County. The freeway serves commuters west to Westminster and Boulder via connections with U.S. 36, and northeast Denver and Aurora beyond the east end with I-70.
The freeway accommodates six lanes of traffic between I-25 and I-76, and just four southeast to I-70. Together with Interstate 76 west to Arvada and Wheat Ridge, I-270 provides a bypass of the oldest section of I-70 through north Denver.
Preliminary numbering for I-270 connecting I-80S (now I-76) and Stapleton International Airport identified it as part of Route A25, a circumferential highway around the east side of Denver along with what became I-225. Communication between the Colorado Department of Highways and the American Association of State Highway Officials (AASHO) in 1958/59 resulted in subsequent suggestions. The first proposal renumbered I-A25 as I-E25, as it would provide an eastern bypass for Interstate 25.
The Colorado Department of Highways then outlined partitioning I-25E into I-225 for the loop south from I-70 through Aurora, and I-425 for the connection northwest from I-70 to I-25 via Commerce City. The designation changed to Interstate 270 once the planned west end of I-80S was changed from a point along I-70 in Denver northward to I-25 over the westernmost section of I-425. This was approved by AASHO on February 26, 1959.1
Construction of the freeway began on December 12, 1965, with $2.7 million in projects including bridges over Dahlia Street, the Quebec Street overpass, and spans for I-270 over Interstate 70. The initial three miles opened to traffic northwest from I-70 to Vasquez Boulevard (U.S. 6-85). Further work on the two mile link between U.S. 6-85 and I-80S followed with completion on October 23, 1970.2
Construction on the extension west to U.S. 36 (Boulder-Denver Turnpike) and Interstate 25 started in April 1993. Coupled with work to lengthen I-76 from I-25 to Pecos Street, Phase I built an eastbound bridge for I-270 over I-25 and rebuilt the U.S. 36 east to I-25 north and southbound ramps. The $11.4 million phase was completed in June 1994. Subsequent construction started in June 1996 for the westbound I-270 bridges over Washington Street and I-25, and a bridge connecting I-25 north with U.S. 36 west. That construction ran through May 1998 and cost $12 million.2
Costing $12 million, additional work from July 1997 to December 1998 built the I-270 westbound bridge over Clear Creek with associated construction for U.S. 36 over Broadway and the I-25 southbound ramp to U.S. 36 west. The westbound extension of Interstate 270 was completed in February 2000 as part of an $19 million improvement project for I-25 and U.S. 36 from June 1998 to June 2001.2 The American Association of State Highway and Transportation Officials (AASHTO) Route Numbering subcommittee approved extending Interstate 270 northwest from I-76 to I-25 on April 7, 2000.