How US Park Police transform traffic flow during morning, evening rush hours in Washington, DC 

Since the 1930s, the Rock Creek and Potomac Parkway has used reversible, one-way traffic operations during the morning and afternoon commutes to help drivers get in and out of the city faster.
But the National Park Service is exploring eliminating one-way traffic operations, and an 81-page report said one reason is the time it takes U.S. Park Police to implement the changes to traffic flow twice a day.
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