This case study focuses on the notable uses of concrete for construction of the Portland, Oregon, MAX (Metropolitan Area eXpress) light rail transit system.

The Tri-County Metropolitan Transportation District of Oregon (Tri-Met) light rail transit system in Portland, known as MAX, has grown from a 15-mile (24-km) line from downtown Portland eastwards, to a 33-mile (53-km), 46-station system spanning from the area’s west side to its east side. From the opening of the Banfield Line in 1986 to the completion of the Westside Light Rail Project in 1998, Tri-Met continues to develop an urban transportation system that is winning multitudes of riders and the appreciation of the community.

During the system’s development, Tri-Met has been refining the design, construction, operation, and maintenance of its facilities. Through all these phases, concrete building materials have offered an infinite variety of applications—providing functionality and durability, while aesthetically enhancing the urban environment.

Trackway

Open Running Track
When Tri-Met began construction of its first light rail line in the 1980s, wood crossties were chosen for most of the at-grade portions of the trackway. After all, the Pacific Northwest is known as the center for timber harvesting and manufacturing in the United States.

A decade later, when Tri-Met began design and construction of the Westside Light Rail Project, several circumstances combined to change Tri-Met’s specifications to concrete crossties. Not only were timber prices at an all-time high, but since the 1980s concrete crosstie track had become accepted practice for light rail systems from Los Angeles to Calgary to Baltimore (heavy rail systems began using concrete ties in the late 1960s). In addition, the focus of decision-making increasingly shifted away from lowest first cost.

By switching to concrete ties, Tri-Met expects reduced maintenance requirements, better alignment retention, increased energy efficiency, and longer durability, while riders experience a smooth, quiet ride.

Street Running Track
In Portland’s downtown (and soon in downtown suburban Hillsboro), light rail vehicles share space with automobile and truck traffic.

Street-running track is constructed with rails anchored by fasteners to a concrete slab. This concrete slab track requires low maintenance, and is highly stable, efficient and long-lasting. A concrete infill is placed to the top of the rails to embed them at street intersections and at special track alignment areas. At other locations in downtown Portland, Belgian block pavers are used to embed the rails.

New construction on the Westside Light Rail Project allowed Tri-Met engineers to get valuable input from maintenance crews who were looking for easier access to the rail for repairs.

The contractor for the downtown Hillsboro street-running track used value engineering (VE) to study alternatives for reducing construction costs. The VE proposal accepted by Tri-Met saved 20% ($1 million) on the 4,500-foot (1,372-m) long double track. Part of the savings was realized by simply using a rubber boot around the rail, which provides electrical protection, as well as noise and vibration attenuation. A test track allowed verification of constructability and performance. The concrete infill is enhanced with a variety of colors, textures, and stamping patterns.

Railway/Roadway Grade Crossings
By the end of 1996, Tri-Met had installed modular concrete grade crossings totaling over 8000 feet (2400 m) of track. Modular concrete crossings were first installed in 1988, when original installations with plastic panels began to fail. More than 2000 track-feet (600 m) have been installed in a retrofit program on the Banfield Line, and all Westside Light Rail Project crossings are of concrete.

Tri-Met prefers the full-depth precast concrete module-type crossing. With this type, the rail is supported directly on a concrete slab, eliminating the need for crossties and ballast. The manufactured modules are ready to be set in place after simple preparation of the subgrade. Rail is laid and a bolted-down concrete center panel holds the rail in alignment. A rubber boot encases the rail to provide not only electrical isolation, but to significantly dampen vibration and reduce noise as well.

The use of precast concrete grade crossing modules has not only improved the ride quality for both transit and motor vehicles, but increased durability and reduced maintenance, as well. Maintenance crews appreciate the easy access to both the rail, for upkeep, and the substrate, for underground utility work.

Project Credits:
Concrete Crosstie Supplier: CXT, Inc., Spokane, WA
Concrete Slab Track
Designer: BRW, Inc., Portland, OR
Contractor: Kajima Eng. & Construction, Pasadena, CA (for downtown Portland)
Stacy & Witbeck, Hillsboro, OR (for downtown Hillsboro)
Concrete Grade Crossing Supplier: Premier Concrete Railroad Crossings, Portland, OR

Intermodal Terminals

Sunset Transit Center
Automobile, bus, bicycle, and pedestrian traffic met light rail trains at the Sunset Transit Center on the Westside Line, when it opened in the fall of 1998. There is a 630-space park-and-ride garage for automobiles, twelve bays for buses, and a pedestrian bridge over the Sunset Highway (U.S. 26) for access to the Cedar Hills Shopping Center. The light rail station occupies an open area 20 ft (6 m) below ground in the midst of these other facilities, offering an easy, convenient connection between transportation modes.

Stairs and elevators bring patrons down to platforms on either side of the tracks. Basalt stone cladding covers the lower concrete masonry walls at the platform level. A simulated tree bark texture on the upper concrete walls provides a sense of nature, without the safety hazard of wood, a visual tie to the forested vistas in the distance. Each platform will be sheltered with a canopy buttressing out from the sides of the open cut.

Bus bays circling the rail station will handle at least ten local bus routes. Bays are constructed of 16-inch (41-cm) thick concrete pavement. Concrete is specified because asphalt does not hold up to the loading of a transit bus. Under the extreme weight of a stationary bus (in excess of 35,000 pounds), asphalt has a tendency to move or flow, causing rutting.

The rails for the two tracks through the platform area are supported on concrete blocks set in a concrete base slab. To the west, the tracks enter a horseshoe-shaped concrete tunnel that takes them first under the parking garage, and then under the highway.

Project Credits
Designer: Zimmer Gunsul Frasca partnership, Portland, OR
Contractor: Wildish Standard Paving, Eugene, OR
Donald M. Drake Co., Portland, OR

Parking Structures

Sunset Transit Center Garage
A major component of the intermodal Sunset Transit Center is its three-level parking structure. The 630-space garage provides direct access to the below-ground light rail platforms and to the bus bays.

This is the second garage the agency has procured as design-build. The procurement process for the Sunset Transit Center garage began with the solicitation of qualifications from joint ventures of contractors and engineering consultants. Tri-Met required that these two entities must be otherwise independent. Conceptual plans were then distributed to the three teams determined by Tri-Met to be the most qualified. These three teams submitted proposals with plans that were up to one-third complete. The proposals were evaluated by Tri-met according to a comprehensive proposal rating system which combines objective elements, such as cost and number of spaces, with subjective elements, such as architecture. This approach allowed the agency to achieve an optimal facility at a minimal cost.

The cast-in-place concrete structure is designed as a moment-resisting frame. This type of structure is specifically suited to Tri-Met’s requirements: it can withstand sizable seismic forces, while still maintaining an openness that provides a sense of security to patrons. To discourage skateboarders and rollerbladers, the concrete surface is heavily tined to produce a very rough finish texture.

Project Credits
Contractor: Yost Grugbe Hall PC and Donald M. Drake Co., Portland, OR

Aerial Guideway Structures
When it came time to select the type of construction for the Westside light rail’s aerial crossing at the Cedar Hills interchange, designers chose a cast-in-place post-tensioned concrete box-girder bridge. The three-span, 434-foot (132-m) long structure is supported by concrete piers consisting of single rectangular columns with rounded ends, and by concrete abutments.

Rails are anchored directly to concrete plinths, or blocks, cast into the concrete deck. This attachment (direct fixation) method eliminates the need for crossties and ballast and their added weight. The loads on the structure are reduced, thereby reducing its own depth and weight. The direct fixation track also eliminates the need for the routine maintenance typically required of ballasted track.

The single cell box-girder design, combined with the direct fixation track, provides the shallowest possible structure. The constant depth box girder results in more clearance for the roadway underneath and reduces vertical gradients for both the roadway and the trackway adjacent to the crossing. This in turn results in less construction impact at the site. To keep the depth constant, even though span lengths varied, the box girder was post-tensioned in the longitudinal direction. The box-girder design, however, results in large cantilevers, or overhangs, on both sides of the deck to accommodate the required width of 31.5 feet (9.6 m) for the two tracks. Consequently, the deck of the box is transversely post-tensioned at 2-foot (0.6-m) intervals to counteract the loads due to these overhangs.

Project Credits
Owner & Engineer: Oregon Department of Transportation
Contractor: Wildish Standard Paving, Eugene, OR
Hamilton Construction, Salem, OR

 
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