#35 – Grade-Separated Crossing Treatments

Boulder, Colorado

Cris Jones, Transportation Planner, Boulder, CO
Contributions by Bill Cowern (Traffic Operations Engineer), Annie Noble (Greenways Coordinator) Marni Ratzel (Bike and Pedestrian Planner) and Randall Rutsch (Senior Transportation Planner).


For over a century, Boulderites have been getting around by bicycle. The city did not, however, emphasize bicyclists and pedestrians in the design of transportation facilities until the 1980s. The 1989 Transportation Master Plan (TMP) brought with it some major changes in how the city viewed transportation. Transportation’s emphasis was moved away from primarily focusing on the automobile, and shifted toward a balanced view of transportation that fully included options like walking, biking, and taking the bus.

Since 1989, the city has seen many changes in transportation facilities, particularly for bicyclists. The planned network of primary and secondary bicycle corridors is largely complete, minus a few key connections that remain to be built. A network of continuous paths along Boulder Creek and its tributaries is 70 percent built. Today, Boulder’s bike and pedestrian facilities are among the best in the country.

The city recognizes the importance of providing a variety of transportation options that allow citizens to travel safely and efficiently. All of Boulder’s transportation facilities include several elements that have been embraced by the community. Bike and pedestrian underpasses have been such a success that they are now used throughout the city. In explaining how the city has come to provide over 55 underpasses, it is important to consider the history leading to their construction.

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. He recommended against the construction of a deep, artificial flood channel to facilitate development in the floodplain. Instead he suggested that Boulder Creek be allowed to remain in a small shallow channel for the ordinary stages of the stream, while including a much broader floodplain as a channel during larger storms. Recognizing the need to dedicate this floodplain land to a useful purpose, he suggested creating a space for public use.

In 1969, a moderate flood affected the city of Boulder. The following decade marked the city’s first serious flood control efforts. Initial investigations focused on traditional flood mitigation techniques, such as hard-lining stream channels and using concrete structural facilities to channelize stream flow. These plans, however, conflicted with the city’s commitment to improve both quality of life and the urban environment, and evoked considerable public opposition.

With the goal of maintaining and enhancing the aesthetic and environmental integrity of Boulder Creek and its tributaries, the city decided to pursue alternative solutions to flood control. In 1978, the city adopted a “non-containment” policy for Boulder Creek as part of the Boulder Valley Comprehensive Plan. 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 development of a continuous path along the entire length of Boulder Creek. This corridor would serve both as a flood hazard mitigation measure and as a continuous urban park for recreational and transportation use. It would also serve to restore and enhance wetlands along with fish and wildlife habitats.

Figure 1. Construction of the Boulder Creek Path underpass at Broadway.

Figure 2. The completed Boulder Creek Path underpass at Broadway.

Figure 3. Pedestrian underpass at College and Broadway.

The construction of a continuous shared-use facility required separated grade crossings at each intersection throughout the corridor. Existing creek underpasses were converted to include shared-use path underpasses through fairly simple modifications. Upon its completion, the Boulder Creek Path was instantly popular and quickly became a much loved community amenity (figures 1 and 2).

The public acclaim of the Boulder Creek project led to an increase in public discussion about the desirability of extending and continuing the concept of the Boulder Creek project along Boulder Creek’s tributaries within the city. As a result, the city designated over 32.2 km (20 mi) of stream corridors along six tributaries of Boulder Creek for inclusion in the Greenways Program.


Today, the city of Boulder is home to more than 55 underpasses built to serve bicyclists and pedestrians. While most new underpass projects are driven by the transportation department, underpasses often have benefits beyond transportation. New underpasses along Boulder’s greenways have increased flood carrying capacity and improved the natural environmental systems along Boulder Creek and its tributaries.

Although most underpasses have been built as a part of Boulder’s greenway system, a number of underpasses have 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, in order to get between campus and the University Hill commercial district. Students often crossed (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. This was largely because of concerns from the merchants in the Hill commercial district. Merchants 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 (see figure 3).

Evaluation and Results

The success and support of Boulder’s underpasses is measured by several elements benefiting the community. These include increasing the safety and convenience of bicycle and pedestrian travel, promoting their use, and in the case of the Greenways system, providing a continuous grade-separated system appropriate for users who are not comfortable using the on-street system. The city currently employs several methods to assess the value of its underpasses relative to its transportation goals. These methods include automated pedestrian and bike counts and periodic surveys used to calculate bicycle and pedestrian mode share.

In addition to routine evaluation methods, the city updates its Transportation Master Plan (TMP) approximately every six to seven years in order to ensure the city is working toward the current needs of the community. The 1989 TMP created a vision of a grade-separated system along Boulder’s greenways. This vision was refined in the 1996 TMP update with its recognition of different types of users from the novice to the experienced commuter and goal of providing facilities for all types of users. Underpass construction continues to be strongly supported by Boulder citizens and evaluation of TMP policies will determine the extent of future construction.

The planning and design efforts resulted in an award-winning project widely hailed as a complete success. Today, the College and Broadway underpass allows thousands of bicyclists, pedestrians, and motor vehicles to travel freely and safely through the intersection every day.

As mentioned above, several methods are employed to evaluate underpass use and benefit. User counts are performed at several locations throughout the city including the Broadway and College underpass. Although counts are not available for dates prior to construction, current counts indicate a high number of users. If the underpass did not exist, current users would be forced to cross Broadway at grade (figure 4). Counts at Broadway and College are taken once a month from 4:45pm to 5:30pm.

In addition to performing manual counts, the city operates several automated bike counters along several shared-use pathways. These counters monitor use 24 hours a day, 365 days a year. Counts have revealed fairly stable use of about 600 to 800 cyclists per day year-round, excluding days of extreme cold, precipitation, and high winds.

Conclusions and Recommendations

As the city of Boulder continues to move toward completing its greenway corridors, it is important to consider the factors that have lead to the city’s success (for other communities interested in building a similar system). As mentioned above, much of the success of the greenways system and its underpasses can be attributed to a community that views such a system as beneficial. It also is important to remember that the system has not been built entirely on city dollars. About 50 percent of funding has come from federal resources.

Costs and Funding

The cost of constructing a grade-separated transportation system 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 multi-modal 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 multi-modal network that has driven transportation efforts in the city. 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 flood mitigation elements. Please see the table listing of some recent underpass projects and their funding sources.

Table 3
Greenway Project Description/Goals Funding
South Boulder Creek Central to Stazio Trail construction including low water crossing and railroad underpass.
  • $67,000 (Lottery)
  • $70,000 (Flood Control)
Bear Creek Baseline to US 36 though CU property One underpass and trail connections to CU Main campus, Apache Trail and Williams Village.
  • $8,700 (Transportation)
  • $58,000 (Flood Control)
  • (FAUS)
Wonderland Creek Broadway Underpass Flood capacity increase, channel restoration, riparian vegetation restoration, wetland and pond creation.
  • $45,000 (Transportation)
Wonderland Creek Valmont Underpass Flood capacity increase, trail underpass.
  • $30,000 (Transportation)
  • $45,000 (Flood Control)
  • (FAUS)
South Boulder Creek Stazio to Arapahoe Paved trail construction, railroad underpass, wetland creation.
  • $57,000 (Lottery)
  • $6,000 (Transportation)
  • $55,000 (Flood Control)
Bear Canyon Creek Mohawk to Gilpin Riparian habitat widening and restoration, wetland creation, landscaping and two underpasses, trail construction.
  • $28,000 (Lottery)
  • $55,000 (Transportation)
  • $84,000 (Flood Control)
South Boulder Creek Arapahoe Underpass Trail underpass.
  • $93,000 (Lottery)
  • $55,000 (Transportation)
  • $45,000 (Flood Control)
South Boulder Creek EBCC Pedestrian Bridge New trail bridge and soft-surface trail approaches.
  • $18,000 (Lottery)
  • $2,000 (Flood Control)
Bear Canyon Creek Martin to Moorhead Food improvements, two underpasses, trail connections.
  • $148,000 (Lottery)
  • $335,000 (Transportation)
  • $599,000 (Flood Control)
Fourmile Broadway Underpass Trail underpass and flood capacity improvements.
  • $4,000 (Lottery)
  • $75,500 (Transportation)
  • $10,000 (Flood Control)
Goose Creek Trail Connection at 30th Street Trail through new 30th Street underpass to Mapleton.
  • $9,000 (Transportation)
  • $1,000 (Flood Control)
Bear Creek Mohawk Underpass Trail underpass and flood capacity improvements.
  • $93,000 (Transportation)
  • $75,000 (Flood Control)
  • $200,000 (Urban Drainage)
South Boulder Creek Baseline to EBCC Underpass, habitat restoration and trail connection.
  • $61,000 (Transportation)
  • $82,000 (Lottery)
  • $52,000 (Flood Control)
Bear Creek Gilpin Underpass Flood control, pedestrian and bicycle underpass.
  • $6,500 (Lottery)
  • $63,000 (Flood Control)
  • $211,000 (Transportation)
  • $97,000 (Urban Drainage)




Bill Cowern
Traffic Operations Engineer
1739 Broadway, 2nd Floor
P.O. Box 791
Boulder, CO 80306-5498
(303) 441-3266

Cris Jones
Transportation Planner
1739 Broadway, 2nd Floor
P.O. Box 791
Boulder, CO 80306-5498
(303) 441-3266

Annie Noble
Greenways Manager
1739 Broadway, 2nd Floor
P.O. Box 791
Boulder, CO 80306-5498
(303) 441-3266

Marni Ratzel
Bike and Pedestrian Planner
1739 Broadway, 2nd Floor
P.O. Box 791
Boulder, CO 80306-5498
(303) 441-3266