TULSA, Oklahoma - The City of Tulsa Traffic Department began closing down streets in downtown Thursday in preparation for this weekend's Williams Route 66 Marathon. 

Around 20,000 people are expected to participate in the annual event. 

Several streets in the Brady District closed Thursday including Cameron between Cincinnati and Boston. 

The city will close more streets Friday morning. The city says Cincinnati will be closed from north of Cameron to Archer. Brady will be closed from Boston to Cincinnati. 

On Saturday a number of streets across downtown and midtown Tulsa will close and remain closed until Sunday evening.

For race course maps visit the Williams Route 66 Marathon web site. For a detailed map of street closures, visit the City of Tulsa's page.