I received a press release from LA Department of Transportation regarding Downtown Street Closures for May Day.  They are as follow.

FOR IMMEDIATE RELEASE Contact: Bruce Gillman
Public Information Office Bruce.Gillman@lacity.org
LOS ANGELES DEPARTMENT OF TRANSPORTATION ANTICIPATES MAY 1, 2009 INTERRUPTIONS FOR DASH DOWNTOWN LOS ANGELES AND COMMUTER EXPRESS ROUTES SERVING DOWNTOWN
LOS ANGELES (April 30, 2009)—The City of Los Angeles, Department of Transportation
(LADOT) is anticipating DASH Downtown and Commuter Express bus service slowdowns, possible service disruptions and/or service cancellations on Friday May 1, 2009 due to the Labor and Immigration Marches and Rally that will occur throughout the day. Street closures and severely impacted traffic flow are expected within the area bounded by Cesar Chavez Avenue to the north, Alameda Street to the east, Pico Boulevard to the south and Hoover Street to the west.
“LADOT will endeavor to keep our DASH Downtown LA and Commuter Express buses running as efficiently as possible under the circumstances. We encourage Downtown workers, residents and visitors to use other transit alternatives such as Metro’s Red Line, Blue Line and Gold Line or Metrolink, to travel in and out of Downtown on Friday. We will be working closely with LAPD in order to keep Downtown area traffic moving, but we do expect significant impacts” said Rita L. Robinson, General Manager, LADOT.
Specific routing changes will be announced on board buses on April 30, 2009 as well as on the LADOT transit website at www.ladottransit.com.. In addition, on May 1, LADOT’s transit web site will be updated hourly to reflect current bus information.
Area commuters can visit http://trafficinfo.lacity.org/ for real-time traffic information and more detailed information on each march’s route. Real-time traffic reports are a product of LADOT, innovators of Automated Traffic Surveillance and Control System (ATSAC) technology.
For specific information about DASH Downtown or Commuter Express routes, schedules or fares, please visit our website at www.ladottransit.com or call (213, 310, 323 or 818) 808-2273.

Plan accordingly.