It's Miami Marathon weekend — if you plan to drive anywhere in the cities of Miami or Miami Beach this weekend, read this first.

The weekend-long event will begin with the Tropical 5K at 7:30 a.m. tomorrow at the Miami Children's Museum. Runners will head east on the MacArthur Causeway toward Miami Beach, turn right onto Alton Road, hang a left onto South Pointe Drive, and finish at Nikki Beach.

Then comes the Miami Marathon and Half Marathon Sunday morning. Hordes of runners will arrive at the starting line before dawn, and several roads will be shut down for hours to accommodate the races. Organizers expect more than 21,000 participants.

The Sunday races begin at 6 a.m. at the American Airlines Arena and end at Bayfront Park. The marathon course runs east on the MacArthur Causeway into Miami Beach and north up Ocean Drive, then west to return to the mainland via the Venetian Causeway and south into Coconut Grove.

So if you don't want to be stuck in traffic waiting for tens of thousands of runners to cross the road, avoid these areas during these hours:

• Downtown/Brickell, 6 a.m. to 2 p.m.
• MacArthur Causeway, 5 a.m. to 8 a.m.
• Miami Beach, 5 a.m. to 10 p.m.
• Venetian Causeway, 6 a.m. to 10 a.m.
• Rickenbacker Causeway, 6:30 a.m. to noon
• Coconut Grove, 7 a.m. to 1 p.m.

Marathon organizers say most runners will be off the course by 2 p.m., but roads will reopen on a rolling basis. Drivers should use the Julia Tuttle Causeway to drive to and from Miami Beach. The Port of Miami will be open and can be accessed from NE Fifth Street. Here's a full list of road closures.

Miami Marathon lore has it that a Miami Heat/Chicago Bulls game coincided with the race in 2012. Rather than decompose in traffic, LeBron James opted for a 40-minute bike ride to the American Airlines Arena. The Heat won that day. And surely that's symbolic of something.

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