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With roughly 45,000 runners pounding the pavement and more than a million people crowding the street to watch, tracking any particular runner is a challenge.
But technology introduced at last year's Bank of America Chicago Marathon is back to help make things easier.
The "Runner Tracking" system allows spectators to follow up to 20 runners along the race course by receiving real-time updates via text message, Facebook and Twitter. Updates will be received as runners cross the 10K, halfway (13.1 miles) and 30K checkpoints, as well as the finish line.
For those who want to follow runners the old fashioned way, a list of update centers and spectator viewing areas are available on the Chicago Marathon website.