The Fred Hutchinson Cancer Research Center, Group Health Cooperative, UW Medicine and Amazon are offering to pay $65,000 for a yearlong experiment to increase South Lake Union streetcar service during the afternoon commute.

Employers are betting $65,000 that if the South Lake Union streetcar runs more often, more commuters will want to ride.

The money will fund a yearlong experiment starting in June to add a third train, so a streetcar arrives every 10 minutes between 4 p.m. and 6:30 p.m. weekdays, if the Seattle City Council approves.

The Fred Hutchinson Cancer Research Center, Group Health Cooperative, UW Medicine and, along with Mayor Mike McGinn, announced the proposal Wednesday.

Shortly after the streetcar opened in December 2007, trains often rolled nearly empty.

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But these days, it’s not unusual to see afternoon trains with 30 or 40 people aboard. Boardings are up more than one-third compared with 2010, reaching 2,250 boardings per weekday in April.

“The ridership has been increasing. It’s proving itself,” said McGinn, who said he was skeptical a few years ago.

Frequent service would help commuters reach their express buses at Westlake Center more reliably, or hop a Link light-rail train sooner.

“If you have to wait 15 minutes, it takes just a little too long,” said Shelly DaRonche, transportation manager for the Hutch.

The arrival of new Amazon buildings and employees is boosting demand.

DaRonche said streetcar spending makes more sense for employees than does underground parking, at a cost of about $60,000 per new slot. “We want to have our parking available for patients to come to visit.”

McGinn was asked whether it’s fair for the tony neighborhood to gain service as other areas face possible cuts.

“If we can get a little more from private investors, that will free money for other uses; it’s a deal we’ll take,” he said.

To some citizens, the streetcar symbolized a Seattle government kowtowing to Paul Allen’s Vulcan, largest landowner in the corridor. But private firms paid almost half the $53 million capital cost.

A second streetcar, funded by Sound Transit, is to open in 2013 connecting Capitol Hill, First Hill and the International District/Chinatown station.

Mike Lindblom: 206-515-5631 or