HOUSTON -

Downtown Houston this weekend will be filled with spectators and about 20,000 runners for the Chevron Houston Marathon.

This is the largest single day sporting event for Houston raising more than $50 million in economic revenue.

For the marathon and half marathon, all the runners will be checking in at the George R. Brown Convention Center, but everyone should be prepared for some security changes, including that all bags entering the venue may be searched.

Whitney Parks says this has been a long journey. She just started running a year ago and has lost 100 lbs. along the way.

"To prove to myself I can do it," said Parks. "With running it's mind over matter; all mental. Once you get out there on the road lace your shoes up its a freeing experience."

It's an amazing run to do or watch. But everyone should know there's some changes.

"Starting on new start line on Congress up to Washington corridor all the way to Kirby district then picking up the old course, we're really excited to show it off," said Wade Morehead, Executive Director of Houston Marathon Committee.

For the last 20 months the route has been the focus because of construction. And in the midst of planning some big security issues needed to be implemented after the Boston Marathon bombing.

"Let me just say they will see a significant increase of police presence at key locations," said Assistant Chief Mark Eisenman, HPD Homeland Security Command.

Local, state and federal agencies are working together. A lot of specifics can't be released, but expect security checkpoints at these four key locations:

•Lamar and Crawford
•Lamar and Avenida de las Americas
•McKinney and Crawford
•Walker and Avenida de las Americas

The checkpoints will be open Sat. from 5:30 a.m. to 10:30 a.m. and Sun. from 4 a.m. to 2 p.m.

Organizers are urging people to leave purses and backpacks at home and to only bring the race-issued clear Gear Check bags.

Participants carrying only their Gear Check bag will not be searched and can enter Discovery Green and the George R. Brown Convention Center without delay. Clear bags that contain other bags will not be accepted at Gear Check.

Discovery Green is open to the general public for those who want to fill the bleachers to cheer on friends and loved ones crossing the finish line.

For more information on security during the 2014 Chevron Houston Marathon Race Weekend, visit ChevronHoustonMarathon.com.