How expensive are Austin's new light rail design options?

In a few weeks' time, Austinites will learn the design and route behind the city's initial investment into light rail transit service.

AUSTIN (KXAN) -- In a few weeks' time, Austinites will learn the design and route behind the city's initial investment into light rail transit service. Project Connect leaders are expected to deliver a final design recommendation at the Austin Transit Partnership's May 24 meeting, with an official vote and decision expected on June 6.

It comes after ATP debuted five initial investment options March 21. The proposals came after project heads paused light rail design work last summer amid anticipated cost increases. ATP is now giving further insight into the costs behind each of the design options on the table, and the benefits and tradeoffs that come with each.

• North Lamar Transit Center to Pleasant Valley Road (on street): $4.8 billion to $4.9 billion
• 38th Street to Oltorf Street to Yellow Jacket Lane (on street): $4.5 billion to $4.8 billion
• 29th Street to Oltorf Street to Yellow Jacket Lane (partially elevated): $4.3 billion to $4.5 billion
• 29th Street to Austin-Bergstrom International Airport (on street): $4.6 billion to $4.7 billion
• University of Texas at Austin to Yellow Jacket Lane (partially underground): $5.0 billion to $5.1 billion

The key cost distinction between the five options is whether the entirety of the route is at street level -- the cheapest offering -- or if a portion of the route downtown is either elevated or underground.

Lindsay Wood, ATP's executive vice president for engineering and construction, told KXAN Wednesday the light rail's downtown orientation will determine the estimated project costs, as well as impact the length of the route.

"Downtown kind of adds a cost premium: It's a little more expensive, even at street level, to be downtown, because we have more utilities. We have more real estate complexities," she said.

Compared to outside the downtown core, Wood said traveling at street level through downtown adds about 25% of additional cost toward constructing it. When considering an elevated light rail path downtown, that cost increases by approximately 66%. The most expensive iteration is an underground tunnel through downtown, adding a cost premium of approximately 300% to the costs of constructing the light rail outside the downtown core.

To mitigate the overall expense of the initial light rail investment, partially elevated or underground options feature shorter routes, with fewer miles of light rail services available.

Beyond costs, though, come the accessibility components of each option. Members of Project Connect's community advisory committee last week indicated a preference for on-street options, in part due to the ways people with various levels of mobility could access the light rail stations sans the need for elevators, escalators or other resources.

Peter Mullan, executive vice president for architecture and urban design, echoed those same points Wednesday.

"There is some advantage to be on the street because you're just closer to the rest of the pedestrian network," he said. "You don't have to use an elevator to make a transition to the station platform, so it's just a more direct and seamless connection."

With three options featuring street-level services, it begs the question: How will the light rail marry into the downtown streetscape system?

Regardless of which design is selected, Wood said the light rail would exist within its own lane and guideway, as opposed to sharing a lane with vehicular traffic. For street-level operations, it'll come down to precise signalization of intersections to ensure a smooth route for light rail trains.

"Those signals for the traffic intersections will communicate with the train control signals, and the traffic signals will know exactly where the train is at every moment in time so they can synchronize when those cross (traffic) movements that would conflict with the train movement can move without inhibiting the train movements," she said.

When a train stops at a station to let off or intake passengers, the light rail will then wait for the next green light before it can begin traveling to the next station.

Once it secures that green light, the signal system will work so that the light rail continues having all green lights until it reaches the next station. While it's loading and unloading riders, cross traffic running perpendicular to the light rail will be able to proceed.

As Project Connect leaders narrow down on its selection for an initial light rail investment, city officials are also evaluating the downtown streetscape. Currently, city leaders are evaluating how to best optimize downtown roadways for all modes of traffic -- pedestrians, vehicles and cyclists.

As Project Connect designs solidify, city staff will also take into account whichever light rail option is selected and how downtown roads can evolve to support all transit modes.

"I think we have the great opportunity right now to look at all these issues holistically, right, and come up with a holistic solution for all of downtown that can accommodate and really support enhanced mobility on all of these modes," Mullan said. "It's a rare opportunity to be able to solve for all those things together, as well, especially in a complex urban environment."

More details on the light rail proposals under consideration are available online.