Dart hits the bull's-eye

June 5, 2008

There is little denying that an expansion of rapid transit in the Dallas area is sorely needed. It is reported that northern Texans spend, on average, about 61 hours of every year sitting in traffic.

There is little denying that an expansion of rapid transit in the Dallas area is sorely needed. It is reported that northern Texans spend, on average, about 61 hours of every year sitting in traffic.

Meanwhile, projections for traffic volume on I-35E, the main artery into and out of the city from the north, show an increase of 45% by 2025. To alleviate the problem, the Dallas Area Rapid Transit (DART) has committed to building out several parts of the system throughout the city. Dallas-based Dowager Construction is handling the southeast corridor of DART’s Green Line extension, which when complete will add 27.7 miles and 20 stations to the system and run from the historic Deep Ellum section of the city northward to Farmers Branch/North Carrollton. According to Madison Smart, the firm’s project superintendent, the job is massive but is still only a portion of the overall light-rail expansion.

DARTing out of traffic

“There are also ongoing extensions to the Orange and Blue lines,” Smart said. “All told, DART has budgeted $1.67 billion to build out several parts of this project throughout the city. It is, at least for the time being, one of the largest transportation projects in America; this section alone carries a price tag of $375 million. Studies have shown that light-rail growth like we are seeing here helps create pockets of specialized developments, both commercial and residential—a real plus for the local economies. It is also believed that the expanded rail line will help join north and south Dallas, areas that have traditionally been divided by the Trinity River. There are a lot of benefits to this expansion.”

Because Dallas has hundreds of miles of rail lines already in place throughout the city and surrounding areas, DART has acquired rights-of-way on some of those existing rail lines and is building the new rail for the balance. In areas in which new track is being put down, said Smart, efforts have to be made to ensure that groundwater flows away from the track bed.

“That involves installation of an underdrain system, and we are doing a huge amount of that type of work on this project—more than we’ve ever done on a single job,” he said. “In fact, by project’s end, there will be better than 120,000 ft of underdrain—about 25 miles’ worth—in place to help draw water away from the rail bed.”

The underdrain process involves placement of a layer of aggregate and, according to Smart, given limited access to some areas, that is the facet of the job in which a Terex PS6000 site dumper is paying big dividends.

Tight confines

While the overall scope of the DART project is massive, the work area in which Smart and his crew have to operate is generally quite narrow, creating a unique set of challenges for material movement and placement.

“In some places, the right-of-way may be only 65 to 70 ft wide,” he said. “In other areas, the rail runs between ballast walls, which might be only 22 ft apart or less. To complicate matters further, within this rail bed area there can be things such as catenary poles, manholes for electrical and subsystem work and more. We have to get aggregate into these areas in advance of the underdrain, and in some cases it can be next to impossible.”

Perhaps the most challenging areas, according to Smart, are the newly constructed light-rail stations themselves, which depending upon the design can either have passenger platforms on both sides or just one in the middle.

“In station areas, the rail section can be as little as 91/2 ft wide,” he said. “What all of these different areas have in common, however, is the limited amount of work area, and because of that, the Terex PS600 site dumper has proven an extremely valuable tool to have around. At less than 8 ft wide, the unit is narrow enough to allow ease of movement, and because the dump bucket swivels 180°, we can get right next to the ditch, turn the bed and dump the aggregate.”

Best of both worlds

According to Walt Robertson, sales representative for Four Seasons Equipment, which is introducing the vehicles to the Dallas-Fort Worth Metroplex, the Terex PS6000 site dumper seems to provide two benefits that usually are self-excluding: capacity and compact size.

“Generally, you have to forsake one for the other,” he said. “If you want small size you have to accept a small payload. If you want that bigger payload, you have to give up access to tighter areas. The Terex PS6000 affords contractors like Dowager the best of both worlds: a payload of better than 13,000 lb and a nice mobile machine.”

Smart estimates that Dowager Construction’s portion of the DART expansion project will keep them in that area for 24 to 30 months, while the overall project will be ongoing for the next five years or so.

—Larry Trojak with Trojak Communications

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