If you missed – or forgot about – the alert earlier this week, here it is one more time: Big events this weekend PLUS closures for the I-5 Mercer exit *and* the 520 floating bridge = potential traffic backups around the region. So say the local transportation departments, including SDOT, which is out with its weekend roundup of what’s happening where. (The Alaskan Way Viaduct *is* open this weekend – but remember that NEXT Saturday, June 25, it is scheduled to be closed most of the day for the Rock ‘n’ Roll Marathon.)