We need more sports teams owned by rich guys but with their own stadiums funded by sales taxes. I say this because light rail ridership is at its best when there are things going on in the stadiums. The suburbanites park their cars in the "Park & Ride" commuter lots at Tukwila and ride in, forcing those of us who use the light rail for our daily commute and who have the misfortune to live a hair closer to town than Tukwila to stand all the way. Seattle's light rail is an odd hybrid. The one line runs only between downtown and the airport, but it takes a detour through the Rainier Valley so it can do double duty as a commuter line.
I don't know what the predictions were, but I can assure you it is being constantly (and often over-)ridden.
Plus when the Anthropogenic Global Warming situation pushes our temps into the 100s, the light rail is the best AC-ed spot in town.