Dreamforce traffic nightmares have only just begun

Traffic on Howard Street is diverted onto Third Street as construction crews build sets for the Dreamforce conference at Moscone Center in San Francisco, Calif. on Friday, Sept. 21, 2018. The one block stretch of Howard is closed between Third and Fourth streets for the annual conference hosted by Salesforce, which features a national park theme and is expected to draw as many as 170,000 attendees. less Traffic on Howard Street is diverted onto Third Street as construction crews build sets for the Dreamforce conference at Moscone Center in San Francisco, Calif. on Friday, Sept. 21, 2018. The one block stretch ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 29 Caption Close Dreamforce traffic nightmares have only just begun 1 / 29 Back to Gallery

UPDATE: It was announced Tuesday afternoon that a major crack was discovered in a steel beam that supports the roof garden of the new Transbay Transit Center. The discovery prompted street closures and consequentially more traffic problems in the area. Read the full story here.

Traffic near Moscone Center, the epicenter of the huge Dreamforce tech conference, is anything but a dream.

With Howard Street closed between Third and Fourth streets, always-busy Third Street into downtown was backed up more than a block early Tuesday morning with slowdowns extending toward Interstate 80.

Delays are expected to worsen and remain sluggish for hours, if not all day.

Dreamforce, a conference for customers of Salesforce, is expected to draw 170,000 conference attendees and thousands more workers to downtown San Francisco from Tuesday to Friday, crowding streets, sidewalks, restaurants and bars downtown.

Traffic delays are expected to persist throughout the week.

Parking control officers will be stationed throughout the area to keep vehicles moving, but commuters are advised to take public transportation or prepare for a slog through the South of Market neighborhood.

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan