Grade-Separated Crossing Treatments

Boulder, Colorado

Prepared by Cris Jones, Transportation Planner, Boulder, Colorado. 2014 updates by Krista Nordback and Jill Mead.

Background

The City of Boulder has always needed to accommodate flash floods. In 1910, Frederick Law Olmsted, Jr. warned the City of Boulder of the dangers of allowing development to encroach upon the floodplain of Boulder Creek. Recognizing the need to dedicate this floodplain land to a useful purpose, he suggested creating a space for public use.

With the goal of maintaining and enhancing the aesthetic and environmental integrity of Boulder Creek and its tributaries, the city adopted a "non-containment" policy for Boulder Creek as part of the Boulder Valley Comprehensive Plan in 1978. This policy promoted ongoing city efforts to protect public safety by restricting development within the floodplain of Boulder Creek and its tributaries. In 1984, the city adopted the Boulder Creek Corridor Plan that recommended the development of a continuous path along the entire length of Boulder Creek to serve as both a flood hazard mitigation measure and as a continuous urban park for recreational and transportation use. The construction of a continuous shared-use facility required the construction of separated grade crossings at each intersection throughout the corridor and existing creek underpasses were converted to include shared-use path underpasses through fairly simple modifications.

Construction of the Boulder Creek Path underpass at Broadway.

Countermeasures

Upon its completion, the Boulder Creek Path was instantly popular and quickly became a much loved community amenity. The public acclaim of the Boulder Creek project led to the extension of the concept to Boulder Creek's tributaries within the city. As a result, the Greenways Program has created stream corridors along fourteen tributaries of Boulder Creek.

Today, the City of Boulder is home to 75 underpasses built to provide grade-separated crossings for bicyclists on more than 300 miles of dedicated bikeways. While most new underpass projects have been driven by the transportation department, new underpasses along Boulder's greenways have increased flood carrying capacity and improved the natural environmental systems along Boulder Creek and its tributaries.

The completed Boulder Creek Path underpass at Broadway.

Although most underpasses have been built as a part of Boulder's greenway system, a number of underpasses have also been constructed at locations not along a waterway. These underpasses serve to eliminate pedestrian barriers and increase safety at dangerous intersections. The College and Broadway underpass, for instance, was designed with the sole purpose of increasing pedestrian safety.

Before construction of the College and Broadway underpass, thousands of students a day were forced to cross Broadway (U.S. Highway 92) at-grade, to get between campus and the University Hill commercial district. Students often crossed at midblock and would stand in the median before crossing entirely. Unlike most of the underpasses within the city, the Broadway and College underpass required a lengthy public process before construction. Merchants in the Hill commercial district worried that an unattractive or poorly designed underpass would be perceived as unsafe and discourage pedestrian traffic to their businesses. The city went through an extensive design process, including obtaining public input, and creating photo simulations of the proposed design to gain community acceptance.

Rendering of pedestrian underpass at College and Broadway used to create community support for the project.

Evaluation and Results

Boulder's network of bike paths and underpasses has increased the safety and convenience of bicycle and pedestrian travel, and in the case of the Greenways system, provided a continuous grade-separated system appropriate for users who are not comfortable using the on-street system. Barring rare events of motorists leaving the roadway, compared to on-street intersection locations, underpasses have practically zero risk of motorist-bicyclist collisions.

Annual counts collected by volunteers, and continuous counts collected using automated bicycle counters provide details about the growth of bicycling in Boulder over time. The graph shown in Figure 1 was created with data from automated counters at path locations and shows the growth of bicycling over time on the Greenways. The average number of bicyclists per day increased from 259 in 2004, to 461 in 2010, with a peak of 487 in 2008.

Figure 1: Number of bicyclists counted by automated bicycle counters at path locations

At the same time that Boulder's bicycle network has grown, more residents have chosen to bicycle to get to work as well as to fulfill their basic needs. Figure 2 shows the percent of trips taken by bicycle for all purposes (blue) and for work (red). The percentage of all trips by bicycle grew from 9.1 percent in 1990 to 18.7 percent in 2012, while the percentage of work trips by bicycle grew from 10.6 percent to 26.5 percent in that same period. Many researchers have noted that as the number of bicyclists on the roads increases, the risk of an individual bicyclist being involved in a collision with a motorist decreases. Thus, the increasing mode share in Boulder has likely improved safety for bicyclists on the road.

The flood-containing potential of the network of underpasses was tested during the extensive flash floods of summer 2013. Although many underpasses were temporarily closed due to debris and sedimentation from the floods, the extensive underpass system was credited with preventing much worse flood damage than what occurred.

Conclusions and Recommendations

Much of the success of the Greenways system and its underpasses can be attributed to a community that views such a system as beneficial. Because the underpasses serve multiple objectives, they are viewed as an essential part of the flood control and safe transportation networks of Boulder.

Costs and Funding

The cost of constructing grade-separated bicycle infrastructure is a discouraging factor for many communities. It often is purported that high sales tax revenues have afforded the city's desire to construct such an extensive multimodal transportation system. In actuality, Boulder's sales tax revenues are average among cities of similar size. It is the community's vision of responsible growth and commitment to a multimodal network that has driven transportation efforts. In addition to commitment, the rapid and extensive construction of underpasses throughout the city has depended on funding leverage. Many underpass projects have received Federal funding based on their flood mitigation elements.

Several entities maintain the Greenways system, and construction and maintenance activities funding comes from the City's Transportation Fund, Stormwater and Flood Control Utility Fund and the State's Lottery Fund, each of which provides $150,000 annually, for a total of $450,000 per year. Additional funding is provided by Urban Drainage and Flood Control District.

Contact

Bill Cowern
Traffic Operations Engineer
1739 Broadway, 2nd Floor
P.O. Box 791
Boulder, CO 80306-5498