Colorado State Highway 470

In the 1960s the Colorado Department of Transportation perceived a need for a beltway around the Denver Metro Area and sent a proposal to the Federal Highway Administration. The plan was for the federal government to provide 90% of funds for the project with the state providing the difference. I-470 was added to the Federal Highway Act of 1968 and was to be part of the Interstate Highway and Defense System. The Denver City Council approved the location and began engineering and environmental impact studies. After a few months the studies went under analysis with negative feedback. The Colorado Department of Health was opposed to the interstate beltway on the grounds that it would violate the Federal Clean Air Act. Other studies compared the proposed I-470 to the I-25 and I-225 freeways suggesting that alternate uses for the land (other than freeways) would be more environmentally friendly.

In response to feedback from the Colorado Department of Health, the governor ordered all efforts to plan and build the beltway to cease. A separate commission was established by Governor Richard Lamm to determine the best course of action. The commission came up with 11 alternatives. The final decision was to use federal highway funds to build a grand parkway known as Centennial Parkway (a partial beltway in the southwest portion of the metro area) and widen existing roads.

As the southwestern area grew rapidly, plans for Centennial Parkway evolved to conform to freeway standards. The proposed road was designated State Highway 470. Present-day SH 470 is a freeway that is mostly built to interstate standards.

After the completion of C-470 in the southwest, desires for a full beltway persisted in some circles and plans for an extension were created. CDOT did not wish to participate in the building of the freeway extension and left the counties and cities of the metro area to provide funding for the project. The east, north, and northwest portions of the beltway could only be built as tollways. Tolled express lanes along the C-470 portion of the beltway with two westbound toll lanes from Interstate 25 to Colorado Boulevard (no interchange), one westbound toll lane from Colorado Boulevard to State Route 121 (Wadsworth Boulevard), and one eastbound toll lane from just west of the Platte River overpass to Interstate 25 are completed and the state of Colorado has began collecting tolls on August 18, 2020.[3]

A tollway extension of SH 470, east and north of the SH 470 eastern terminus, was built to the junction with State Highway 83 (Parker Road) and termed Eastern/Extension 470 or E-470. Subsequently, E-470 was extended to the interchange with I-70 in the east, and later to I-25 in the north. This newly added tollway was built and continues to be administered by a quasi-governmental organization known as the E-470 Public Highway Authority.

When freeway interests pushed for the rest of the beltway to be completed, the city of Golden voted to stop all efforts to finish the beltway due to traffic concerns. The city and county of Broomfield, Colorado constructed a 11-mile (18 km) continuation of the E-470 tollway from I-25 to an interchange with US 36 (the former Denver-Boulder Turnpike) near Flatiron Crossing Mall. This section of the tollway is known as the Northwest Parkway, and is administered, similarly to E-470, by its own quasi-governmental agency. In conjunction with E-470 (47 miles) and SH 470 (27 miles), the Northwest Parkway brings the total length of the completed portion of the beltway around the Denver-Aurora Metropolitan Area to approximately 85 miles (137 km). The uncompleted portion, from the west end of the Northwest Parkway to the northwest end of SH 470, is 19 miles (31 km) along existing streets.

In 2007, the Portuguese company BRISA paid $603 million to operate the road for the following 99 years, until 2106.[4][5] The lease included a clause restricting a "Competing Transportation Facility. This clause was invoked in an April 30, 2008 letter when Broomfield wished to make changes to 160th Ave.

As of August 2003, CDOT made a compromise with the cities of Westminster, Arvada and Golden to do an environmental impact study, the first step in an attempt to complete the beltway by 2020. The last segment of the beltway would be another tollway, tentatively called W-470, and would connect the west end of the Northwest Parkway to the northwest end of SH 470.

The Jefferson Parkway is the planned extension to the beltway to begin at the Northwest Parkway and end at SH 93. It is currently in its planning phase. Jefferson County, Broomfield and Arvada have formed the Jefferson Parkway Public Highway Authority to construct the freeway. If the 20-mile parkway is constructed, Denver will be completely encircled by a "metropolitan beltway."[6]