Number 15 bus, you are no longer welcome on the Morrison Bridge.

In the latest attempt to cope with the quick deterioration of Portland's busiest non-highway span, Multnomah County announced today that vehicles over 10 tons won't be allowed on the Morrison beginning April 13. That means nothing for your Miata, but Trimet and C-Tran buses, and any other monstrous conveyances traveling from I-84 and I-5 to downtown (or vice versa) will have to find another route.

The county's also cutting speed limits on the bridge, from 35 to 25 mph.

"We’ve got the deck that’s only three years old that has problems," County spokesman Mike Pullen says. "We’re adding band-aids. We’d like to get the heavy loads off."

The new strictures are the most dramatic response to date for the worrying deterioration of the bridge's polymer lift span decking, which has begun to crack up below the surface. Earlier this month, a jury found the county and four private entities shared the blame for the shoddy project, completed in 2012. Taxpayers will pay at least $1.2 million for the flawed deck, with other parties splitting the rest of the cost $5.6 million cost.

The county hopes keeping heavy trucks off the bridge will prevent further deterioration, though Pullen says no one can guarantee that's the case. Officials are trying to find a suitable replacement for the polymer deck and may announce new plans in April.

You can read a full account of the many missteps that have gone into the Morrison project here.

Pullen says the county will also open two lanes on the Morrison—closed over safety concerns—once the weight limits go into effect. The Portland Police Bureau will patrol the bridge, and issue warnings or tickets to trucks that flout the ban, consciously or unconsciously.