A rendering of the a pedestrian bridge connecting Crystal City to Reagan National Airport over the George Washington Memorial Parkway. The bridge is included in the deal Virginia, Arlington and Alexandria made with Amazon. (CC2DCA)

Over a decade, a once-industrial Seattle neighborhood transformed into a burgeoning commuter hub with streetcar and bus connections, bus lanes, cyclists and private shuttles ferrying employees to the complex of buildings that comprise the headquarters for the online retail giant Amazon.com.

Among workers in that city’s South Lake Union neighborhood, about 30 percent of commuters take public transit, nearly a fifth walk to work, around 15 percent carpool or van-pool, and many others bike, according to data compiled in state-required surveys. One in 5 who work for Amazon walk to their jobs. Amazon employees’ transit costs are fully covered by company-subsidized passes. (Amazon founder and chief executive Jeffrey P. Bezos owns The Washington Post.)

Now as attention shifts to Crystal City in Arlington, Va. which will split Amazon’s second headquarters with New York, the question becomes whether South Lake Union’s commuting successes — what the transit industry calls “mode split” — can be replicated 2,300 miles across the country.

“I would certainly hope it’s replicable — the numbers are pretty good,” said Andrew Glass Hastings, former director of transit and mobility for the Seattle Department of Transportation. “They have certainly set a precedent in Seattle, and that precedent is working, so I would certainly hope they try to apply the same logic to any place they choose to locate.”

Amazon’s move to Crystal City — or National Landing, as the company will re-brand the area where it will build its hub — could have a dramatic impact on the transportation network in a region that already has some of the worst traffic in the country and a subway grappling with falling ridership.

Virginia, Arlington and Alexandria said they were spending more than half a billion dollars to support Amazon’s plans, much of it on existing projects. The plans included an additional entrance to the Crystal City Metro station and a second entrance for the planned Potomac Yard station.

The plans also include a pedestrian bridge from Reagan National Airport to Crystal City and a transit-way expansion in a corridor with the region’s only bus rapid transit system, along with improvements to Route 1.

Arlington and Alexandria’s pledged investments totaled $570 million, while Virginia said it was investing $195 million in improvements; the funding would go to new projects and the expansion of existing ones. The plan would tie new transportation funding levels from the state to the number of jobs Amazon creates.

Unlike in Seattle, where voters rejected a federally subsidized mass-transit system that was ultimately awarded to Atlanta in the 1970s, the Washington region already has an extensive rail system — one that could use an influx of riders.

But it is a delicate balance. A traffic meltdown during a partial Metro shutdown including National Airport this past weekend highlighted what can happen when one part of the network breaks down and the system becomes overwhelmed.

Still, the potential of thousands of new riders is welcome news for the Washington Metropolitan Area Transit Authority, which has seen declining Metro ridership cut into operating revenue, leading to service cuts and higher fares for the system’s 600,000 average weekday riders.

Metro General Manager Paul J. Wiedefeld said Amazon officials made a point of riding Metro when they were touring the area during site visits. “To me that sent a signal that they were extremely serious about transit and they were extremely serious about Metro’s role in the region,” he said.

“It just further supports the need for investment,” Wiedefeld said. “It supports the need that we have to improve the service. It supports the need to expand the service where we can. And so I think from that perspective it is getting us to where we all want to be with the transit system.”

Wiedefeld did not rule out the possibility of a station name change to go along with Amazon’s re-branding of the area as National Landing, though he said station names are typically geographical or landmark-based and any decision was “to be determined.”

Experts and transit advocates hope the need to eventually serve 25,000 employees and potentially their families could speed up needed transportation projects and lead to improvements in a corridor along Metro’s Blue and Yellow lines that is served by an international airport; subway, bus and commuter rail service; bus rapid transit; and several major highways that feed into the District.

A new 900-foot pedestrian bridge linking National Airport to Crystal City would make it perhaps the most prominent U.S. airport accessible on foot and establish it as an “ ‘aerotropolis’ connecting an estimated 10,000 airport passengers to Crystal City per month,” according to a feasibility study issued by the Crystal City Business Improvement District in February.

The project would cost $16 million to $38 million (depending on whether it is a bridge or tunnel), according to the study. The Crystal City BID held two public meetings on the bridge study late last year and found the project was feasible, identifying federal, state, regional and local sources of potential funding.

“Amazon was looking for an urban and transit-oriented environment, and they certainly have found one in the most pro-transit, pro-smart-growth jurisdiction in the country in Arlington County,” said Stewart Schwartz, executive director of the Coalition for Smarter Growth. “It’s a good thing in that we would be focusing these jobs where we have excellent transit and close to the core of the region so that the jobs are accessible 360 degrees around.”

Schwartz noted an added benefit: Amazon’s selection of Crystal City could lead to a new “reverse commute” in which riders are filling empty trains headed outbound from the District — in the opposite direction of rush-hour travel.

Advocates say the region’s selection is a testament to its robust transit coverage and presents an argument for adding service at a time when chronic reliability problems are sending Metro riders to other modes. But it comes with inherent risks — of exacerbating gridlock, crowding Metro lines on a system unprepared for the surge of riders or sending more commuters back to the roads via ride-hail services and driving.

D.C. Mayor Muriel E. Bowser (D) called Amazon’s choice of Crystal City a “win for D.C.” but highlighted Metro as a priority for improvement.

“We must continue our investment in safety, reliability, and capacity at Metro and find ways to enhance service, including late night service,” Bowser said in statement.

D.C. Council member Charles Allen (D-Ward 6) said the top priority for the city should be planning for infrastructure and transportation overhauls.

“If 25,000 jobs means 25,000 more cars, transportation is not going to work,” Allen said. “While it provides a whole lot of opportunity, there’s a whole lot of risk and a whole lot of challenges when it comes to investments that are going to be needed so we aren’t moving everyone around by cars.”

Analysts say there is also no guarantee that new workers and their families will choose Metro.

“Metro has really got to become its own best advocate by having the kind of services they used to have,” said Paul Mackie, director of research and communications for Mobility Lab, the research arm of Arlington County Commuter Services. “Metro has to make itself really attractive to get them to choose Metro over the many other options perhaps people are finding more attractive at this point.”

A recent internal Metro report highlighted population and jobs near stations as the top factors driving rail ridership. That makes Amazon a potential windfall.

“For every 10 percent increase in population within a half-mile of stations, ridership is expected to increase by 2.4 to 3.1 percent,” the report said.

Amazon has historically given generous transit incentives to its workers and in Seattle has even provided operating funds — spending $1.5 million to increase bus frequency and ease crowding in popular corridors in the city.

“I think it will be a very big plus for Metro, because we’ll have more riders, more people who want to ride Metro,” said Jack Evans, chair of the Metro board. “And Metro, then, is going to have to be in a position to deliver.”

While few details were available on the transportation plans — aside from short summaries — the feasibility study laid out in detail the benefit officials said the pedestrian bridge could bring.

“A new pedestrian connection would enable travelers to avoid potential road congestion or long waits on Metro with an enjoyable, 5-minute walk,” the study said. “It would also harness the multitude of transportation assets in Crystal City, seamlessly link them together into a multimodal hub, and position the neighborhood to attract additional rail service operations such as Amtrak, regional commuter rail, and even a future high-speed rail station.”

Meanwhile, the head of the Transportation Security Administration, David Pekoske, said a $1 billion project underway to build a new commuter concourse and expand and modernize security checkpoints at National Airport is well-timed and “will certainly help” any additional passenger traffic generated by Amazon’s expansion.

Advocates were bullish on other potential improvements. For example, Schwartz said Amazon’s arrival could lead to the expansion of dedicated bus lanes for Metroway, the bus rapid transit system linking Arlington and Alexandria that already has its own right of way in the most congested corridors. Smart-growth advocates are pushing for Virginia Railway Express station upgrades to expand capacity and service, along with better bike connections in the vicinity of the new headquarters and the linking of the Metroway system with other bus rapid transit, such as the recently approved Richmond Highway Bus Rapid Transit in Fairfax County.

Whether Metro is able to capi­tal­ize on the additional riders, officials say the impact of just the potential of Amazon choosing the Washington region is clear.

“Amazon was the impetus that certainly turned Maryland in supporting the dedicated funding,” Evans said. “I think Amazon was the catalyst that got Maryland and to some extent Virginia on board.”

A spokeswoman for Maryland Gov. Larry Hogan (R) disputed that characterization, however, saying Amazon’s search and Hogan’s position on Metro funding were unrelated.

Affordable-housing advocates have warned that the arrival of tens of thousands of high-income workers could displace residents in and near Arlington and drive up rents, sending some residents to car-dependent suburbs and worsening gridlock. Meanwhile, some fear under that scenario that well-paid workers would turn to a mode of transportation they have been shown to prefer — ride-hailing. A Seattle Times analysis published this month identified South Lake Union as one of the city’s most popular neighborhoods for Uber and Lyft.

“That’s certainly going to be a major factor,” Seattle’s Glass Hastings said. “If people can’t access transit easily, if people can’t walk or bike, Lyft and Uber are very prevalent in that area, as well.”

Lori Aratani and Fenit Nirappil contributed to this report.