A blue line guides runners from Staten Island, through the five boroughs and to the finish line in Central Park each year.
On Sunday, a yellow line also appears for the last 400 meters of the race, in honor of the victims of last April's attacks.
The subtle tribute was called a "line of inspiration" by New York Road Runner CEO Mary Wittenberg. "That line will be a line to the future and a line that represents our unity with Boston.
Yellow and blue are the colors of the Boston Athletic Association.
Security has been a major focus in the aftermath of the bombings.
All 45,000 runners will be screened, and their bags will be checked, at the start point Sunday morning. A total of 1,500 TV-quality surveillance cameras have been trained on the course – especially concentrated on the finish line area.
Police helicopters, harbor units and scuba divers also have been assigned.
There will also be 49 police dogs on the ground, including specially-trained canine units that can detect explosives moving through a crowd.
"Two years ago there was security, but not nearly like this," said runner Jane Kinsella of Hauppauge.
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