City Clamps Down As Authorities Ramp Up Search For Terror Threat

<p>Police increased security on the subways yesterday.</p>

<p>Security checkpoints spur gridlock as 9/11 anniversary approaches.</p>

<p>The happiest bomb-sniffing dog in the world</p>

<p>A police officer examines the rear section of a truck at a vehicle check point yesterday.</p>

<p>A New York City police officer stops Xiang Mao, left, and Lexi Li along the perimeter of the World Trade Center, Thursday, Sept. 8, 2011 in New York. The officer's hand-held radiation detector indicated that one of the two may have had radioactive material. Xiang Mao explained that he had been injected with radioactive material for medical tests Wednesday. The two tourists from Canton, China were allowed to continue on their way.</p>

<p>A midtown police checkpoint</p>

<p>Mayor Bloomberg inspires confidence by riding the subway yesterday</p>