The urban design of the 15th Street Modifications Project is intended to recreate 15th Street as the primary vehicular and pedestrian connection between the Lower Downtown Historic District, the Central Platte Valley, and the neighborhoods to the northwest. Historically, 15th Street had been this connection, prior to construction of a viaduct.

The project began with an Environmental Assessment report, which defined the project issues as impact and accessibility to existing development; adequacy and location of utilities; vehicular circulation between I-25 and downtown; conformity to Central Platte Planning; impacts on cultural and historic elements; natural environmental effects; and maintenance of existing rail operations.

The EA report recommended the removal of the existing viaduct and replacement with an underpass beneath the Consolidated Mainline railroad tracks on the 15th Street alignment with an at-grade roadway entering Lower Downtown between Delgany and Blake Streets. The result of the improved street and sidewalk would be the recreation of the historic function of 15th Street as the connection between downtown, Central Platte Valley and the neighborhoods to the northwest.

The design of the project accommodated both the Lower Downtown Streetscape Design Guidelines for the area within the Historic District and the Urban Design Guidelines established as part of the Central Platte Valley Comprehensive Plan. The latter defines overall visual continuity amongst the new public infrastructure improvements in the valley- a "Family of Structures."

Fifteenth Street in Denver, CO recreates the scale and pedestrian amenities of traditional streets in the city's lower downtown neighborhoods including street trees, decorative paving, improved street crossings, and traditional pedestrian lighting, benches and railings. A new block-long plaza between Blake and Wazee Streets introduces the only urban open-space in this portion of Lower Downtown and serves as the "front door" to five previously vacant buildings now being restored for mixed commercial and retail use.

The design of the underpass creates a vehicular entry to downtown, a comfortable and attractive pedestrian environment, and a high quality of civic architecture in support of existing uses in the area and as an attraction to future redevelopment in the Central Platted Valley. The underpass utilizes horizontally articulated, stepped back walls with vertical pilasters, decorative sidewalks, pedestrian lighting, benches and railings, street trees, special pedestrian bridges crossing over the roadway, stairs connecting to existing grade and the integration of public art provide an attractive and safe sidewalk for pedestrians. Handicap accessibility is provided per ADA standards.

An attractive plaza and "front door" onto the sidewalk is also provided for the historic Moffat Station. The visibility of and accessibility to other vintage warehouse and commercial buildings in the area is similarly enhanced, thereby strengthening the connection between the Historic District and the Central Platte Valley. A new north-south street will connect 15th Street with the future extension of the 16th Street Mall to the north and to the site of the Elitch Gardens amusement park to the south across Cherry Creek. Wynkoop Street, another existing crossing street, was repaved with salvaged brick to recreate its traditional character and to provide an improved pedestrian connection to the Speer Boulevard/Cherry Creek recreational trail utilizing an existing steel railroad truss bridge. A similar opportunity exists at Delgany Street.

The structure that carries the Consolidated Mainline railroad tracks over 15th Street and the pedestrian bridges are designed as traditional railroad bridges to reflect the historic context of the area. The 15th Street project is a major addition to Denver's commitment to excellence in its civic architecture.