TR Circular E-C058_9th LRT Conference_2003.pdf - Florida ...

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cheaper than steel, saving $100,000 in material costs. The use of plastic bollards also eliminated
the need for grounding, yet another direct cost savings. Because LRT design criteria requires all
conductive materials within 15 ft of the trackway to be electrically grounded, removing the
grounding requirement saved an additional $150,000.
Recycled Plastic Track Ties—Moderate Tech The paved track portion of Interstate MAX
uses 6,000 ties spaced every 6 ft, to maintain alignment, gauge, and grade, until the concrete
track slab was poured. On previous light rail projects steel ties were used. Interstate MAX used
ties made from recycled polyethylene automobile gas tanks. These ties have the added advantage
of not affecting the signal system, unlike steel ties. Not having to shield the signal system from
the steel ties offer yet another cost savings.
Storm Water Management
The design basis for the Interstate MAX project’s storm water system is the City of Portland’s
Storm Water Management Manual. Project staff and engineers from the City’s Bureau of
Environmental Services formed a design task force to implement the City code. The team faced
the challenge of applying rules intended for a typical city block development to a linear project
5.6 mi long, crossing 12 separate drainage basins, seven of which drain into the Columbia
Slough, and five of which drain into the Willamette River. The task was also complicated
because Interstate sewer system was in large part combined (sanitary and storm), with only the
lower sections (those in Lower Albina, close to the Willamette River) being separated. The city’s
rules dictated that the project treat (i.e., clean) the storm water using one of a number of
approved best management practices. The joint agency team weighed the factors and decided to
install treatment manholes on key storm pipes, thereby treat a large percentage of storm water in
the Lower Albina section of the project. When all of the project’s total impervious area was
calculated along Interstate Avenue, there was a net reduction. Although the road was widened to
add the track, approximately 1.3 mi were constructed as open ballasted track. The replacement of
asphalt paved roadway with ballasted track removed a 28-ft strip of impervious surface area.
Storm Water Treatment Manholes—Moderate Tech The team selected Continuous
Deflection System water treatment manholes for the project. The manhole utilized a unique (high
tech) deflection screen that reportedly removes 95% of solid pollutants.
This was one of several techniques that were approved by the City; however, it had some
key advantages favored by the project:
1. Hydraulics advantages. This system did not require any head drop (differential
between pipe inlet and pipe outlet) through the treatment structure. This meant money was
focused on treatment structures and not on laying extra pipe chasing grade downstream to tie
back into the sewer system.
2. High flow effectiveness. The manholes tolerated a wide range of flows. The first
flush and flows were treated and the high flows were diverted without resuspending the captured
pollutants.
3. Ease of maintenance. The City’s bureaus were charged with maintenance, and with
limited resources this was important. This is a good example of considering the life-cycle cost of
a potential project element in selecting a particular design or facility.