Resources and Library:

Bridges and Structures for Trails

Hosted by AmericanTrails.org

 

A new bridge flies over railroad tracks and seven-lane Hiawatha Avenue to link two major commuter bikeways. At the east end, the Light Rail Trail provides a high-speed bike commuter and recreation corridor into downtown Minneapolis. At the west end of the bridge the Midtown Greenway provides a key linkage in a trail system that stretches 25 miles west into the suburbs.

This project was nominated for a Planning/Design Award as part of the 2008 National Trails Awards, announced at the 19th National Trails Symposium in Little Rock, Arkansas.

 

Sabo Bridge connects Minneapolis commuter trails and transit


Photos by Stuart Macdonald, October 29, 2010

Background

The Martin Olav Sabo Bridge, opened in November 2007, soars over major obstacles to make a critical link in major bikeways. The Midtown Greenway is a multi-use trail that runs east-to-west through south-central Minneapolis. This trail is located in a former rail corridor, and— because it is located below-grade— it has few street-level crossings.

photo of big curving bridge

The new bridge from the air showing trail approaches

Near the eastern end of the Midtown Greenway, the trail crosses Hiawatha Avenue (Minnesota Truck Highway 55). This road has six divided lanes of traffic plus additional turning lanes and ramps. The highway has an average daily traffic count of approximately 45,000 and a posted speed of 40 mph at crossing location.

The bike and pedestrian crossing of this highway is at a signalized intersection with a large number of cars making right turns across the crosswalk to access the highway. Observation of the bike/pedestrian crossing indicated long waits to cross the intersection, often leading to unsafe crossings by cyclists and to pedestrians stranded in the middle of the intersection.

The Midtown Greenway is also notable because it runs through a neighborhood with a high proportion of economically disadvantaged and immigrant populations. A high percentage does not have vehicles and must rely on transit, walking and biking to get places. The street-level crossing of Hiawatha Avenue creates a barrier between these residents (living on the west of the highway) and the retail and employment on the east side of the highway.

This section of the Greenway was experiencing almost 2,500 average daily bike counts in July 2007— with counts reaching 3,500 on peak days. The increasing use of the trail at that crossing had the potential of leading to additional conflicts as vehicles, bikes, and pedestrians attempt to cross within the narrow existing crosswalk.

photo of new bridge

Cable anchors for the Bridge with the trail along
Hiawatha Avenue going underneath

 

Challenges and Solutions

Hennepin County’s Regional Rail Authority owns most of the property upon which the Greenway was built. After examining several alternatives, the County determined that a bridge crossing would provide the safest route for pedestrians and bikers across the highway. Putting a bridge crossing over Hiawatha Avenue at this location, however, was very challenging.

The Hiawatha light rail transit (LRT) line runs parallel to Hiawatha Avenue and is elevated above highway and trail at this point. In addition, a set of high-voltage power lines runs parallel to the LRT line and Hiawatha Avenue on the east side of the road. Given the various rights-of-way and clearance requirements for the highway, LRT line, and high-voltage power lines, there are significant limitations to where and how the bridge and its supports could be located.

In order for a bridge to fit within the complex infrastructure already onsite, the Crossing would need to veer north to enable the bike and pedestrian bridge to cross over the highway, 23 feet OVER the light rail transit track (and its overhead power lines) while at the same time staying 25 feet UNDER the high powered transmission lines. At the same time, bridge approaches would need to be designed to meet ADA requirements of a maximum grade of 5 percent. To accomplish this grade, the bridge and its approaches would need to follow an almost U-shaped curve over the freeway and rail line.

Public and Multi-jurisdictional Participation

Hennepin County brought together a wide array of stakeholders to be involved in this effort, including the City of Minneapolis, the Minnesota Department of Transportation, the regional transit agency (Metro Transit) and local elected officials. In addition, the project had over a dozen meetings to seek input from nine neighborhood organizations, local businesses, interested non-profit groups, and the local electric utility. The bridge design process included multiple roundtable discussions with County and City staff, the construction consultants (URS), civil and architectural professionals, and community leadership.

Photo of horses on the trail

On the bridge looking west

One of the challenges with this type of project is trying to convey technical engineering details in a way that allows the public to envision the actual project. Hennepin County and URS prepared realistic and technically correct bridge renderings to inform and elicit feedback on the design and to educate the audience on different bridge concepts and their relationship in the adjacent environment.

They also prepared animated 3-D visualizations to provide a cyclist’s perspective crossing the bridge as well as perspectives from the highway and LRT line. These renderings and visualizations were utilized in meetings with the public and stakeholders to illustrate how the project would fit in the area. In the end, the investment in this technology saved countless hours of discussion and explanation while providing a clearer view of the project.

Bridge Design

One of the project’s key design decisions stemmed from the public’s concern that the corridor area already contained many dense vertical elements (such as the Hiawatha Avenue freeway bridge and its retaining walls, the LRT bridge and its supports, and another pedestrian bridge further to the north). These elements made the area feel “boxed in,” and as such, the public did not want another large structure in that area. Hennepin County staff worked with URS consultants to design and construct a “transparent” structure that would be large enough to cross the freeway and LRT line without overwhelming the area with its mass. The resulting design was a 215 foot cable-stayed bridge sandwiched between two sharply curving approach spans.

photo of view over railroad from bridge

View from the bridge towards downtown Minneapolis showing
Hiawatha Avenue, the LRT rail line, and the Light Rail Trail

The main span of the bridge is supported by a single 108-foot pylon located on the west side of Hiawatha Avenue. Cables – anchored to large concrete blocks that in turn are anchored into limestone bedrock – support the bridge deck, which ranges from eight to 24 inches in depth. The bridge deck includes a minimum of 18 feet of useable trail width (two five-foot bike lanes and a six-foot pedestrian way). The bridge rails are a stainless steel cable system that provides safety for trail users while also being transparent to users and complementing the linear feel of the bridge structural system.

The bridge includes both pedestrian safety lighting and accent lighting, which allow 24-hour use. There are also emergency phones and security cameras to enhance the safety for users. The total length of the bridge and approaches is approximately 2,200 feet.

Project Results

This signature bridge represents a major investment in the community and is intended to instill civic pride in surrounding neighborhoods with its striking design features. The County’s investment in the bridge acknowledges the needs of these neighborhoods for safe and efficient mobility opportunities and provides an iconic structure which advertises the Midtown Greenway for the motorists and train riders who pass below each day. The bridge celebrates the Greenway and encourages more trail use for commuting, recreation, and commerce. Some of the key successes of this project include the following:

• Involved a planning process that brought together multiple levels of government, the private sector, and community groups to identify the best option for crossing this difficult intersection;

• Fills in a major gap in area’s multi-use trail system:completing the east-to-west link through the heart of Minneapolis;

• Makes it easier for area residents, including those without vehicles, to travel to employment, school, and shopping destinations along the corridor;

• Enhances safety for system users by eliminating an at-grade crossing of a highway; and,

• Creates an architectural and engineering signature structure that fits within the existing light rail transit, power line, and freeway constraints, without adding to the “mass” of structures already in the area.

For more information:

Dean Michalko
Hennepin County Dept of Housing, Community Works, & Transit
417 North 5th Street, Suite 320, Minneapolis MN 55401
Phone: 612-348-6286 - dean.michalko@co.hennepin.mn.us - www.hennepin.us

Print Friendly
Print Friendly and PDF

 

 

 

Facebook Twitter

Stay up to date on legislative issues for trails, follow us on Facebook and Twitter.

 

business directory

 

trail database

Need trail skills and education? Do you provide training? Join the National Trails Training Partnership!

The NTTP Online Calendar connects you with courses, conferences, and trail-related training

arrowEnjoy and share the new online, digital version of the American Trails Magazine!

arrowHelp us provide you more useful resources to keep you on the cutting-edge -- please join today!

arrowWe are advocating for your interests! Visit the Supporting Trails page to view the latest in legislative news, current issues, and opportunities, and to learn how to access funding.

arrow Sign up for American Trails Action Alerts and Trail Tracks e-Newsletters.

 

PDF  Some of our documents are in PDF format and require free Adobe Acrobat Reader software.
  Download Acrobat Reader

section 508 logo American Trails and NTTP support accessibility with Section 508: read more.