A section of SH 119 called the Diagonal Highway exists in what was once considered the outskirts of Boulder, but has since become a very busy area. Reconstruction of the Diagonal Highway was designed to improve roadway durability and drainage while adding pedestrian and bike facilities where there were none.
Complex Multimodal Design, Unique Roadway Elements
This complex design includes an extensive new drainage system, off-street bike lanes, multi-use paths, and improved transit facilities. With 400 trees, 4,400 shrubs, and 2,000 perennials, a number of landscape features were integrated into the design. The added green space is supported by a new irrigation system as well as three rain gardens that collect, store, and filter rain water and storm water runoff to naturally remove pollutants. Public spaces, including art plazas, were part of an emphasis on adding community value. Otak managed the design of this multi-phased project along with significant coordination between multiple departments within the City of Boulder, CDOT, RTD, and community stakeholder groups.
Enhancements to Main Street and the commercial district of Lyons, Colorado design pedestrian mobility, active transportation, drainage, and streetscape improvements. Sidewalks and crossings with refuge islands along US 36 also include bike lanes throughout the corridor.
Streetscape Designed for Multimodal Use
A pedestrian crossing at the Stone Canyon intersection involved a streetscape design that accentuates multi-modal use. The Otak team brought this project from concept to completion while working extensively with the Colorado Department of Transportation (CDOT) throughout the process in achieving a roadway cross section that met the City of Lyons transportation goals.
As part of planning efforts for the Denver metro area, the Southeast Metro Stormwater Authority (SEMSWA) aimed to map disproportionately impacted communities as part of meeting a task order to develop an environmental justice technical presentation. Otak harnessed ArcPro’s spatial analysis tools to map overlays of identified communities (low income, minority communities, and housing cost burdened communities) throughout the SEMSWA service area with Colorado’s EnviroScreen data to show where impacted communities overlap.
Utilizing GIS Mapping to Improve Stormwater Service to Disproportionately Impacted Communities
In producing the “SEMSWA Service Area Environmental Justice: Disproportionately Impacted Communities” presentation, SEMSWA planned to pursue voluntary inclusion of environmental justice considerations in providing services, and prepare for possible inclusion of environmental justice requirements in future permitting. The intent of the map is to identify areas with environmental inequities, pinpoint areas that have disproportionately impacted communities (communities with greater health burden and/or face more environmental risks), and geographically identify disproportionately impacted communities (DICs) based on the definition in Colorado’s Environmental Justice Act. A geographic union was created in GIS to graphically show where multiple DIC communities overlap. The effort intersected SEMSWA’s maintenance areas with the DIC analysis results. By overlaying EnviroScreen data they could better identify areas of interest where SEMSWA provides services that appear to meet the definition of disproportionately impacted communities under the state law.
With the goal of re-establishing its floodplain connectivity, the restoration of St. Vrain Creek enhances aquatic habitats, restores riparian health, and improves stream resiliency. The multi-objective design incorporates features to mitigate future flooding and moderate sediment loads from inundating the Town of Lyons.
Restoring a Floodplain for More Resilient Habitats and Community Flood Mitigation
Central to the design development was a thorough understanding of sediment dynamics and hydraulics. Sediment dynamics were assessed by modeling and comparing reach-scale capacities. The restoration involves approximately 3.2 miles of South St. Vrain Creek, extending from the canyon mouth to the Old St. Vrain Road bridge near the Town of Lyons. Channel hydraulics were assessed by 2D modeling of the study area using the Sedimentation and River Hydraulics 2D (SRH-2D) model, developed by the Bureau of Reclamation. The model informed the design with an understanding of the complex linkages between main channel and floodplain flow, including floodplain benches, overflow channels, and more than a dozen large wood structures throughout the reach. The project team worked with stakeholders to collect feedback and turn concerns into project goals. Otak led the channel restoration design, 2D hydraulic modeling, geomorphology, and sediment transport analyses for this CDBG-DR grant-funded restoration project.
The City of Louisville faced a major challenge in improving South Boulder Road At-Grade crossings to ensure pedestrian safety while also managing federal requirements and associated documentation. Improvements at 5 different intersections involved the installation of pedestrian signals and would all be completed in accordance with CDOT local agency requirements.
Managing a Federally-Funded Project for Pedestrian Safety Improvements
Improvements to South Boulder Road addressed critical issues such as tie-in elevations at each intersection, and updated 30 plus year old traffic signal equipment with new high-intensity activated crosswalk (HAWK) systems while ensuring 13 ADA ramps meet all requirements. As a federally-funded, CDOT agency project, the project involved significant documentation. In close collaboration between all stakeholders, the Otak team led construction management, inspection, and materials testing services. Issues with tie-in elevations of the existing asphalt and the new asphalt were quickly resolved with field adjustments derived from a deep understanding of design concepts which ultimately led to 3% savings on the overall bid.
Adding to an existing trail system, the Airport Road Pedestrian Underpass provides safe crossing beneath eastbound SH 119, as well an at-grade crossing on the roadway’s westbound lanes. The design by Otak was completed while accounting for high traffic volumes, working in close coordination with the Colorado Department of Transportation (CDOT), and includes a number of solutions aimed at optimizing the trail user experience.
Innovative Structural Solutions for a Safer Trail Experience
While adding approximately 4,000 linear feet of trail, the Airport Road Pedestrian Underpass incorporates several innovative design solutions to optimize the user experience. A unified drainage system that addressed the high groundwater table and retaining wall system to avoid tight right-of-way (ROW) impacts are among those design solutions. Groundwater mitigation – with consideration of adjacent wetlands – along with cast-in-place aesthetic features are also included. To facilitate two phases of construction, the project included a temporary shoofly roadway in completing utility relocation, lighting, signal modifications, and modifications to existing driveways.
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.
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