by Tim Croghan, Dennis Nottingham and Burdett B. Lent, ASLA
Alaska's Chugach Mountains can be viewed from inside the portal.
The Tudor Road landscape features Red Cherry plantings.
Coordinated site furnishings and wildflowers soften the structure of the bridge.
Close-up views reveal the Tudor Road bridge's 80-degree curvature (top), detailed tunnel railing and wildflower plantings (above).
For years, the State of Alaska and Municipality of Anchorage had studied ways of crossing the busy, five-lane Tudor Road arterial with a multi-purpose trail-- without success. Close proximity to high voltage power lines, buried utilities, close clearance tolerances, and the desire to have a smooth, continuous crossing with grades less than 5% for use by bikers, the handicapped, and sled dog teams presented difficult design problems.
This multi-purpose trail project provided a critical link in Anchorage's greenbelt trail system. Included were more than 1/2-mile of trail and two grade separations, one for a major arterial and one for a local street. Because this was Anchorage's first ISTEA-financed project, Municipal, Alaska State Department of Transportation and federal criteria applied to the design, and the requirements for document preparation varied from usual requirements.
The Municipality of Anchorage wanted to provide a pleasant and safe, landscaped and separated trail connecting the Campbell Creek, Chester Creek greenbelt trails and the Coastal Trail-- thus forming one gigantic city-wide "loop" for recreational purposes. By creating the trail crossings, it also was anticipated that the overall transportation system would function more smoothly and efficiently. In the summer, many Anchorage workers and University students commute by bicycle, and these crossings would make conditions for both drivers and trail users safer.
This $1.9 million project required full professional services from surveys and soils testing through construction inspection. Services included utilities research, final trail horizontal/vertical alignment, civil/structural engineering for bridge and tunnel, electrical engineering for lighting, utilities engineering, landscape design and community/governmental coordination. Four municipal agencies, two state agencies, a federal agency and a private land owner/developer were all involved in the project. The local Community Council and trail user groups included pedestrians, cyclists, cross-country skiers, and dog mushers.
Interestingly, the trail was designed for both cross-country skiers and dog-mushing teams, as it is a part of the Iditarod and Fur Rondy Race trail systems in the winter. The trail runs through a private office park, whose owner wanted uninterrupted views of a pond and mountains from the buildings-- all of which required raising an entire street and constructing a tunnel. High water tables near the tunnel, buried water, gas, electricity and telephone lines, and high-voltage overhead power lines left limited "windows" through which the trail, bridge and tunnel had to be threaded-- a very challenging set of constraints.
Professional Engineer Dennis Nottingham of the firm Peratrovich, Nottingham & Drage, Inc., (PN&D) acted as prime design consultant, civil and structural designer of the bridge and tunnel. His design-- the use of steel and structural solutions not often considered in conventional approaches-- solved many difficult problems at the site.
A geometric window with 17-foot road and 23-foot power line clearance could only be met with a curved bride, both vertical and horizontal, with no supports other than at abutments. Aesthetics demanded by the trail easement property owner also limited the use of sprawling superstructures in favor of more massive landscaped abutments.
For the 160-foot span bridge, a restrained, 80-degree curved, torsionally-stable, double box-girder orthotropic solution with massive pile-supported concrete abutments was the final solution. The property owner later stated, "The bridge is more than I ever expected. If you (i.e. design engineer) ever need a recommendation, just have them call me."
Steel decks have long had the problem of surfacing or overlay disbonding. For this project, bonding layer impact testing to -70o F produced a solution. A high-solids urethane was found which bonds to the sand-blasted steel deck. Pea gravel broadcast into the bonding layer provided traction for conventional asphalt concrete overlay paving. High seismic ground movement and large thermal changes were easily handled by the curved bridge with no need for any joints. Long-term steel protection from corrosion and discoloration was addressed through the use of spray metalizing with a color coat overlay.
The bridge-- because of its torsional strength and light weight-- was assembled near the crossing, moved, and lifted in one piece. Tudor Road closure was limited to only 24 hours.
For the undercrossing at Ambassador Drive, a lighted reinforced concrete tunnel was used. This provided minimal height for the high water table clearance, and a maximum amount of daylight inside the tunnel. Wing walls, with complementary railings, were designed to blend with the slopes and to reflect light into the tunnel.
As a subconsultant to PN&D, Landscape Architect Burdett Lent, ASLA of Group III Design, performed major work on this project. Assisted by Landscape Architect Marcia Stevens-Foltz, ASLA, Lent handled historical research, proposal writing, negotiations, utilities research, horizontal and vertical trail design, landscape design for trees, shrubs, ground covers, walls and furnishings and coordination with civil, structural, electrical and utilities engineers. The Landscape Architects also assembled PS&E documents, coordinated with governmental agencies, the Municipality's Project Manager, Rachel Rourke-Sunnell, ASLA and various boards, commissions, councils, land owner, and the State's construction management personnel.
The landscape now features twenty different trees and shrubs specifically chosen for the short growing season and for low appeal to the Alaskan Moose. The landscape subcontractor, American Landscaping, assisted with the placement of topsoil, wildflowers and three seed schedules for slope stabilization.
Wildflowers on the site help introduce color to an otherwise very urbanized Alaskan arterial road system and trail. In coordination with the bridge's dark green and beige color scheme, site furnishings (benches and trash receptacles) that repeated the colors were added to the rest areas. Red bike racks and stone enhancements accent the entire design.
Personally dedicated by Anchorage's Mayor Rick Mystrom, the project has won local and national honor awards for design, including the 1996 Celebration of Anchorage Honor Award for overall design.The public has received the highly-visible project very well, and numerous comments about the beauty of the structures and the landscaping have been received. This is unusual because the public usually does not comment on projects like this. But in this case, phone calls and media coverage raved abut the bridge aesthetics. Even the dogs in the sled dog racing teams seem to enjoy the crossing... LASN
All illustrations provided courtesy of Alaska Department of Transportation and consultants.
Tudor Road Plant Palette:
Colorado Green Spruce
Canadian Red Cherry
Dwarf Mugho Pine
Anthony Waterer Spirea
Rugosa Hybrid Rose 'Therese Bugnet'
Three types of seed schedules were used depending on the area of use for slope stabilization and for the use of color with wild flowers. The following seed was used for the project:
Schedule B: Red Fescue, Alsike or Dutch White Clover, Annual Ryegrass, Ox-Eye Daisy, Sunflower Baby Blue Eyes and Iceland Poppy.
Schedule E; Kentucky Bluegrass, Red Fescue, Annual Ryegrass and Ox-Eye Daisy.
Schedule F: Red Fescue, Kentucky Bluegrass, and Manhattan Rye.
Project Team :
Client Municipality of Anchorage/Alaska DOT
Rachel Rourke-Sunnell, ASLA, MOA Project Manager
W. Timothy Croghan, PE, DOT Project Engineer
Project Tudor Road Trail Crossing, Phase I
Funding Federal Highway Administration
Location Anchorage, AK
Developer Municipality of Anchorage, Parks & Recreation
Landscape Architect Group III Design
Burdett B. Lent, ASLA, MLA
Marcia Stephens-Foltz, ASLA
Designer of Record Peratrovich, Nottingham & Drage, Inc.
Dennis Nottingham, PE
Civil Engineering Peratrovich, Nottingham & Drage, Inc.
John Pickering, PE
Structural Engineer Peratrovich, Nottingham & Drage, Inc.
Dennis Nottingham, PE
Electrical EngineerF.P.E. Roen, Inc.
Lighting Designer F.P.E. Roen, Inc.
Graphics Consultant Arlene Mitchell
General Contractor Construction & Rigging, Inc.
Landscape Contractor American Landscaping
Construction Manager William Goodell, DOT Project Manager