By Walt Hunter

MALVERN, Pa., (CBS) — Amtrak now says a broken rail forced the closure of one of two tracks on its East-West Main Line throughout morning rush-hour, causing delays of Amtrak runs to Harrisburg and Pittsburgh and cancellation of all Septa Regional Rail service on the western end of its busiest regional rail line between Malvern and Thorndale.

Crews worked for nearly six hours to fix the track before service was restored at noontime.

“An investigation to determine why the rail broke is underway,” according to a statement emailed by Amtrak officials. “But this episode demonstrates the impact that aging infrastructure can have on service reliability.”

The track problem comes 10 days after a deadly Amtrak derailment at Frankford Junction killed eight and injured nearly 200, igniting a national debate on funding to improve infrastructure.

Amtrak says the broken rail was spotted by one of its personnel as rush hour started and train service was halted immediately so repairs could begin.

The age of the rail, and when it was installed, could not be immediately determined.