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With roughly 45,000 runners pounding the pavement and more than a million people lining the streets trying to get good views, tracking any particular runner is a daunting task.
But technology is aiming to make it easier this year.
The Bank of America Chicago Marathon's "runner tracking" system will send alerts to cell phones as runners cross the 10-kilometer point (6.2 miles), the halfway point (13.1 miles), 30k (18.6 miles) and the finish line.
There's no limit to the number of runners you follow and the system is free to use, aside from charges assessed through your provider.
Web registration on the system is open until 11 p.m. on Saturday. After that time, registration can only be done directly via the phone by sending a text message with the bib number of the runner you want to follow to 99731.