LYNX Light Rail Construction Rides Again in Charlotte
by Jim Parsons
Charlotte's eight-year-old LYNX Blue Line, which attracts more than 15,500 daily riders and has spurred $1.45 billion in development within a half-mile of its 9.6-mile corridor, is frequently touted as a model for cities interested in developing light rail transit systems.
A $1.2-billion, 9.3-mile extension of the Blue Lines is two years away from its fall 2017 start-up date, but it serves as an example of the perseverance necessary to overcome the complex, interrelated challenges of constructing linear infrastructure systems in urban environments.
For instance, to connect the existing Blue Line's Uptown terminus with the University of North Carolina-Charlotte (UNCC) campus to the northeast, the extension's dual tracks, 11 stations and other facilities are being wedged into some of the city's busiest road and freight rail corridors.
Those constraints presented the Charlotte Area Transit System (CATS) with the challenges of extensive utility relocations, coordinating work with long-haul train schedules and developing strategies to preserve access to dozens of businesses along the route during the four-year construction phase.
Due to the current complexities facing the project team, CATS project director Danny Rogers says experience gained from having built more than 11 miles of light rail citywide went only so far.
"This is a different corridor," Rogers says.
That fact was made clear as construction got underway in early 2014 with the task of identifying and coordinating the relocation of "an astronomical number" of above- and below-ground utilities, says Troy Carter, senior project manager for Lane Construction Corp., Cheshire, Conn. The firm is handling civil construction work at a cost of $119 million for segments B and C, which total 4.9 miles. A joint venture of Balfour Beatty Infrastructure, Atlanta, and Blythe Development, Charlotte, is handling the 4.5-mile-long segment A under a $108-million contract.
Additionally, Balfour Beatty holds a $130.8-million contract to build the track and related systems. That contract includes $114.4 million for the new line and $16.4 million for platform and system extensions on the original line.
Before contractors could widen a 4.15-mile stretch of four-lane Tryon Avenue-long one of Charlotte's main through routes-in order to accommodate the Blue Line Extension's 40-ft-wide right-of-way, dozens of utility poles and numerous underground telecommunication and infrastructure lines buried up to 15 ft deep needed to be moved to create sufficient subterranean space for a new storm drainage network and the widened roadway.
Coordinating that work to keep traffic flowing as smoothly as possible would have been difficult enough, Rogers says. But because the individual utilities bore the cost of the relocations, the response tended to be slower than CATS desired.
"The incentive for them to work quickly wasn't as strong as if they were being paid to do it," Rogers says.
To prevent a protracted construction process that would frustrate both motorists and business owners, the construction teams revamped their schedules as utility relocation work was completed. Teams combined what had originally been planned as linear phases into concurrent operations, such as widening the northbound and southbound sides of the highway concurrently rather than one at a time.
Brian Stover, project director for HNTB, which is managing construction services for CATS's Blue Line Extension, says consolidating those tasks helped make up some time, cutting three to four months off the original construction schedule.
"The business owners still had to deal with a lot of activity in front of their locations, but it was completed sooner," Stover says. He notes that the use of tablets equipped with construction management software was essential in keeping the field supervisors up to date with the frequent plan and schedule revisions.
Public outreach likewise played a critical role. "Part of creating sustainable development going forward is protecting what's already there," Rogers says. "You don't want the cure to be part of the illness. We had a dedicated team working to help keep the businesses visible, and alert them to what would be happening in the coming weeks so that they could prepare."
The relocation roles were somewhat reversed for building the extension's four-mile route through the Norfolk Southern-owned rail corridor, which includes as many as four tracks shared by six railroads. With CATS responsible for relocating the existing tracks to make room for the light rail line, "we're essentially working for the railroad," Rogers explains.
That made coordinating construction activity with both freight and passenger railroad operations especially critical.
"We had to figure out how to do as much as possible safely within tight windows of only a few hours," Stover says. "It hasn't been easy, but we've been able to do it."
More problematic, however, has been the project area's pervasive shallow depth rock. Conditions complicated the construction of foundations for three straddle bents and two hammerhead bents, supporting a 735-ft-long, 713-ton steel bridge that lifts the light rail line over the rail tracks and a cross street. In addition to the time-consuming process of drilling 8-ft-dia shafts 80 to 100 ft deep, frequent encounters with subsurface water created the risk of cave-ins. This required the use of temporary casings that were removed as concrete was poured.
"That's pushed the schedule out, so we had to take as much of the drilled shaft work as possible off critical path," Stover says.
Other structures along the Blue Line Extension have proven somewhat less complicated. The 447-ft, three-span curved steel girder bridge that brings the light rail line into the center of Tryon Avenue includes some of the project's 184,630 sq ft of mechanically stabilized earth (MSE) retaining walls. These were fitted with precast panels and cast-in-place textured form lines, which feature patterns of native plants.
To bring the Blue Line Extension onto the UNCC campus, Lane is constructing a 40-ft-deep, 340-ft-long, cut-and-cover underpass beneath Tryon Avenue's northbound lanes that will include a 23-ft by 36-ft cast-in-place box culvert structure, reinforced with one-sided wall formwork and permanent soil nail walls. From there, the 822-ft-long, 11-span precast Toby Creek Viaduct with pre-stressed supports will convey the Blue Line Extension across a wetland to the terminus station.
Despite the marshy floodplain setting, the ever-present subsurface issue of inconsistently sloped bedrock necessitated the use of end-bearing piles drilled 60 to 80 ft deep.
With the Blue Line Extension's civil phase moving toward its scheduled spring 2016 completion, Balfour Beatty Infrastructure will soon begin installing the light rail track; overhead catenary and traction power systems; and train control, signal and communications systems throughout the route. Balfour Beatty also installed the foundations for the extension's 11 stations, which will include 15- to 18-ft-wide side- and center-loaded configurations with 276-ft-long platforms to be constructed along with other elements by station finishes contractor Edison Foard Inc., Charlotte.
In addition, Balfour Beatty is lengthening platforms at three stations along the original segment to 276 ft in order to accommodate three-car trains throughout the entire route.
"Our ridership volume opened higher than expected and will increase quickly once BLE opens because of more destinations," Rogers explains. CATS expects daily ridership to increase from its projected 2018 total of 18,000 passengers to 24,500 by 2035. A one-way trip along the nearly 19-mile line should take about 47 minutes.
Work has also begun on the Blue Line Extension's other vertical elements, including three multilevel precast parking garages with more than 3,300 spaces. A 20,300-sq-ft operations, service and inspection facility is set to get underway later this year.
Gregory Sigmon, project manager for STV, which designed the Blue Line Extension and is managing construction of the garages and maintenance facility for CATS, says the most challenging aspect involved with the design and construction of light rail transit systems is the many complex, interrelated project components. It's a lesson that other cities and contractors exploring light rail lines should be mindful of, he says.
"In a highway project, a signal system may be the most complicated feature," he says. "For light rail, you have numerous systems, alignments, at-grade crossings, revenue collection factors and many other things that have to be managed and coordinated. It's like putting a big puzzle together."