The reconstruction of a 3,700-foot segment of pedestrian path of Cottontail Trail in Boulder Open Space and Mountain Parks improved its longevity. Over a three month duration, Otak played a critical role in evaluating the existing trail and building a team to successfully complete improvements that make the park more sustainable and ADA accessible.
Trail Improvements Add Durability and Accessibility
Cottontail Trail was realigned steep sections to meet ADA grade requirements and ditches for improved drainage. The design also replaced an existing turnpike section to eliminate its need for constant repairs which included an armored ford consisting of a concrete tread section with 24-inch culvert pipes. Colored concrete with exposed aggregate finish was selected to provide a durable, low-maintenance surface that blends well with the rustic rural character of the area. Otak was responsible for ensuring that the work was done right and on schedule despite numerous changes, acting as the eyes and ears for the owner throughout the construction process.
In expanding the city’s extensive trail system to regional transit and developing neighborhood, the CO 42 Underpass provides a safe and user-friendly grade-separated crossing. A concrete box culvert as well as new sidewalk/trail connections and utility relocation were included in the project. In leading the design, Otak also provided project management services during the construction phase.
A User-Friendly Crossing to Increase Active Transportation Connectivity
After completing an Open Space and Trails Wayfinding project – which also led to the McCaslin Boulevard Underpass – identified improvements to the Lake to Lake Trail, the CO 42 pedestrian underpass represents one of several investments by the city in transportation and supports its goal of safe traveling conditions for pedestrians and motorists. By strengthening the city’s approximately 32-mile trail network with better connectivity, the underpass encourages active transportation with more walking, running, and cycling in the community. The construction of a concrete box culvert running underneath CO 42, along with the relocation of several utilities and the Goodhue Ditch, created a pedestrian thoroughfare that closes an important gap in the Lake to Lake Trail.
Crossing beneath Kipling Parkway, this pedestrian and bicycle underpass provides a safe connection as part of the Van Bibber Creek Trail System. In leading the underpass design, Otak provided full construction drawings, bidding documents, cost estimates, and other necessary materials.
A Structure Designed to Provide Safe Crossing for a Trail System
At 8.5-feet-high and 14-feet-wide, the Kipling Parkway Underpass also adds 4,000 linear feet of 10-foot-wide concrete pathway in connecting the Van Bibber Creek Trail. Aesthetic elements for the structure including the lighting and retaining walls were designed to be commensurate with the character of the surrounding area. The project required utilities to be relocated, including a 12-inch water line and irrigation ditch, as well as right-of-way acquisition from a nearby subdivision as well as the Arvada Cemetery. All necessary materials were prepared in accordance with the Colorado Department of Transportation (CDOT) Roadway and Bridge Design Manuals and Standard Specifications for Road and Bridge Construction, the latest edition of the American Association of State Highway Transportation Officials (AASHTO) Manual, and the City of Arvada Engineering Code of Standards and Specifications.
Promoting active transportation and pedestrian safety, the Hover Street Pedestrian Underpass is located just south of the street’s intersection with SH119. With Otak leading structural engineering, the design included relocating a Regional Transportation District (RTD) bus pad directly on top of the underpass to further enhance safety while improving multimodal access.
A Structure to Enhance Pedestrian Safety and Multimodal Access
In designing the overpass, a “jug handle” link trail was used to divert the flow of traffic to allow seamless, safer turns that don’t require crossing oncoming traffic. Named for its distinct shape, this design also allowed for the creation of a plaza area with bike lockers and other site amenities. The project’s emphasis on multimodal access is highlighted by a bus pad located on top of the overpass. Key aesthetic features include multiple concrete formliners and pilaster columns with masonry veneers found on the underpass and headwalls. A detention facility was also added to manage drainage from SH 119 and adjacent business property. Accounting for a complex intersection geometry and high traffic volumes, the project was constructed using a three-phase maintenance of traffic approach.
With approximately 96,000 feet of 36-inch diameter and 14,000 feet of 32-inch diameter raw water transmission pipeline, Southern Water Supply construction also required appurtenances running from Carter Lake in Larimer County south to Boulder Reservoir in Boulder.
Managing Water Pipeline Construction Across a Variety of Environments
Otak’s construction management team oversaw the roadway reconstruction and reclamation efforts for this project, which involved the installation of a 20-mile raw water pipeline that extends from Carter Lake to Boulder Reservoir. The alignment crosses open space, agricultural lands, roadway, streams, wetlands, and ditches. Some areas are environmentally sensitive and have very specific revegetation requirements. In particular, the stream crossings and wetland reclamation must be carefully monitored for compliance with 404 Permit requirements and floodplain regulations.
Over the years, the Jefferson County Open Space (JCOS) system in Colorado experienced rapid growth in visitation numbers. Certain park access areas no longer supported visitor demand during peak season and/or during peak hours as a result, generating congested and sometimes unsafe experiences for visitors. Plans to address a variety of these issues would be put in place with steps in visitor use management.
Solving Park Issues with a Tailored Visitor Use Management Approach
Because some parks have finite space and infrastructure to support current visitor and vehicle use levels, they struggle with a variety of congestion-related issues, all of which include safety concerns. In order to address various issues from trailhead congestion, multimodal access and impacts to natural resources, JCOS worked with Otak and CDR Associates to develop an access management strategy for popular sites across the system by applying visitor use management principles. The resulting access management report evaluated all relevant considerations within a National Park Service tested process to design an approach specific to JCOS for planning and implementation.
The University of Colorado (CU) Boulder’s main campus is separated from student residential areas by Boulder Creek, the Boulder Creek Trail, a riparian corridor, as well as a 30 to 60-foot-tall elevation differential. The 19th Street Bridge establishes accessible connections while providing cost-effective aesthetic appeal at Colorado’s flagship university, bringing to life their vision of creating a “bridge through the canopy,” where pedestrians weave through trees on a structure connecting them with the surrounding environment and quick transportation to their campus destination.
A Low Impact Structural Design for A More Connected and Accessible Campus
To minimize fabrication efforts and construction cost, a series of identical straight 30-foot steel spans were utilized at a near-maximum ADA compliant slope to make the bridge no longer than necessary. Each pier landing serves as a turn point for the pathway to create an overall curve shape out of a series of straight lines. The piers are supported by a single concrete column founded on either a caisson or a micropile foundation, depending on the terrain. Custom railings using weathering steel plates and bars minimize materials and obstruction of the surrounding natural beauty. Lighted handrails shine downward to illuminate the bridge path after dark while minimizing light pollution. Otak designed the bridge with the goals of minimizing impact to the existing hillside, limiting the removal of existing high value trees, and to not disrupt the area’s historic stone structures. The 19th Street Bridge greatly improves the connectivity to campus while providing students, visitors, and Boulder residents a connection to the surrounding nature and landscape for generations.
To provide safe crossing between two open space properties and improve vehicular circulation in the trailhead parking lots, the City of Louisville aimed to add an underpass at McCaslin Boulevard. A redesign of the Davidson Mesa Trailhead would also be included to accommodate more vehicles and increase driver, pedestrian, and vehicular safety with a one-way round-about design.
Multiple Transportation Features for Improved Access and Safety to a Popular Trailhead
In improving vehicular circulation and trailhead access, the design of McCaslin Boulevard Underpass also includes the full reconstruction of two trailhead parking lots at Davidson Mesa and Harper Lake. It’s part of broader improvements to the Lake-to-Lake trail, including the CO 42 Underpass. The location of the underpass and angle of the approach trails were designed to frame and enhance views of the Flatirons (to the West) and Harper Lake (to the East). Natural stone retaining walls and site grading were designed to fit the structure approach between into the natural landscape. The facility was designed for multiple user types, including pedestrians, and bikes. An information Kiosk was designed to keep people informed with events and the Leon A. Wurl Wildlife Sanctuary on the Harper Lake side. Otak provided preliminary design and complete construction documentation in the development of this pubic asset.
This federally funded, 83-ft. long, 20-ft. wide underpass crosses Iris Avenue and Elmer’s Two-Mile Creek in west Boulder. As a combined-use facility for path users and creek flow, the structure is sized to accommodate the 100-year flood within the structure, and the 5-year flood is contained behind the floodwall while providing ADA accessibility.
A Structure Designed for Flood Resilience and Accessibility
The Elmer’s Two-Mile Creek underpass provides a safe and inviting pedestrian connection beneath Iris Avenue. Natural stone and boulder retaining walls, plantings and colored concrete were incorporated in the design to provide an inviting and aesthetically pleasing facility. Geometry is very tight on the north side of the project, requiring close coordination with a homeowner’s association for location of retaining walls and trail access points while providing ADA accessibility at several locations. Due to high groundwater conditions and tailwater elevations, a lift station was required to handle both stormwater and the structure underdrain system. In addition, a low-water crossing is designed with collapsible railings to fold down during a major flood event. Otak provided complete engineering services in bringing this structure to completion while allowing traffic on Iris Avenue to be maintained throughout construction.
A 11.5-mile trail corridor, the St. Vrain Greenway extends from North 75th Street to Weld County Road 7 in Longmont, Colorado. The initial design included six pedestrian bridges along with trail segments adjacent to these bridges, beneath the existing vehicular bridge at Main Street (State Highway 119), and other segments where slopes or site grading was critical.
Extending a Trail Corridor While Minimizing Impact to Habitat
The initial 9.5-mile trail was followed by a two-mile segment of path designed through a riparian corridor and included a 140-foot span pedestrian bridge over St. Vrain Creek while designing for erosion control beneath the existing SH 119 bridge. Ramp connections to bike lanes along the highway, modification to an existing field access bridge, and a new pedestrian underpass structure at 119th Street and East County Line Road were also included as part of the complete St. Vrain Greenway design. Spanning from 25 to 140 feet in crossing St. Vrain Creek, Lefthand Creek, Old Dry Creek, and the Bonus Ditch, the pedestrian bridges used break-away bridge designs – from Design Concepts – in order to reduce construction costs and minimize site impacts. Several alternative path alignments were considered in the conceptual design phase to minimizing impacts to wetlands, wildlife habitat, nesting bald eagles, and other sensitive areas. Otak was involved throughout the project’s phases, from subconsultant on landscape architecture for the six pedestrian bridges to prime for the St. Vrain Greenway path design.
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