Seattle is the fastest growing city in the U.S., thanks largely to Amazon’s addition of 35,000 employees since 2010. For all the economic benefits that come with growth, it has also created a variety of civic headaches, crippling traffic chief among them.

But thanks in part to considerable efforts by the region’s largest employers, the share of commuters driving solo into downtown Seattle is on a dramatic decline.

Just 25 percent of workers traveling into the center city drove themselves, accordin…