Revelers gathered on the Mall to celebrate the Fourth of July yesterday, combining the traditional hot dogs, parades and pyrotechnics with a sobering nod to post-Sept. 11 reality: a test of evacuation routes to be used in the event of a terrorist attack. At the end of an otherwise celebratory day, police set “Operation Fast Forward” into motion at 9:50 p.m., just 15 minutes after the fireworks ended. Over the next 45 minutes, officers directed motorists to four evacuation routes, known as E-routes, where green lights were lengthened from 70 seconds to three minutes, followed by one minute of red. Full Story