BY STEVE ROTHAUS, srothaus@MiamiHerald.com

Police and homeowner activists are warning drivers to brace for "complete gridlock" in parts of Miami and Miami Beach as 4,000 or more Critical Mass bicyclists take over the streets.

"This Friday there is a non-sponsored event that is starting in the City of Miami and impacting our city," according to Miami Beach Patrol Capt. Enrique Doce. "The event is a bike ride that involves a large amount of riders that overtake the lanes of traffic. There is no event organizer to reach out to and in the past they have severely affected the traffic and caused hours of delays. Please make everyone aware and alert to this event. Please distribute the attached advisory to everyone that could be impacted."

From Critical Mass' website:

Friday, April 25th

6:30pm (ride starts at 7:15pm)

Government Center

150 NW First Street

Downtown Miami

The ride will be going through East Little Havana, Overtown, Allapattah, Liberty City, Little Haiti, Upper East Side, North Bay Village, North Beach, Miami Beach, Venetian Islands, and Downtown.The route / map is available here, total distance is approximately 20 miles. It's strongly suggested that you print a copy of the map or save it on your phone in case you are tardy or get lost.

Cyclists ride at their own risk and assume responsibility for their own safety!

Don't forget to bring front and rear bicycle lights. It's the law! We will be leaving at 7:15pm sharp. If you arrive late you will be left behind, the ride starts & ends in Downtown Miami. Rain or shine!

THIS IS NOT A RACE! SLOWER RIDERS TO THE FRONT!

In the past, thousands of drivers have been caught in massive traffic jams, waiting for bicyclists to pass through intersections.

"Be aware that traffic along the below red-lined route will be severely impacted by the bicyclists. You may want to plan your evening accordingly," Miami activist Elvis Cruz shared Friday on a Morningside homeowners email group.

Miami Police say they're aware of – and prepared for -- the impending traffic mess.

"We do monitor the lights. We stop traffic for the bikers to go through so no one gets hit or gets hurt. That's our first priority, safety," Miami Police Public Information Officer Frederica Burden said.

The city plans to have police at intersections throughout the bike route, which winds from Government Center in downtown Miami, north on Northwest Seventh Avenue, east on 54th Street to Biscayne Boulevard, then north to 79th Street Causeway.

It's up to patrol officers whether to stop bike traffic for motorists, Burden said.

"It's at the discretion of the officer on the street," she said.