Tolling on the Highway 520 floating bridge across Lake Washington has begun, and traffic remained light in the early morning.

Thursday marked the first day commuters were charged to cross the heavily used span. But many key questions remain, specifically how many drivers are using the "Good to Go" stickers, which allow automatic billing? Or how many plan to revolt and driver around the bridge or use Interstate 90? which is not tolled for now.

State transportation officials have said they expect Thursday's traffic on the 520 bridge to be much lighter than usual. Traffic is already down because of the holiday week.

Officials say the real test will come next Tuesday, when more people return to work.

As of Wednesday, 520 toll system director Patty Rubstello said only about 20 percent of regular bridge commuters had their debit sticker installed.

Those without the sticker will be billed by mail for the toll - plus a $1.50 surcharge.