The Federal Railroad Administration does not allow for the mixing of train types for safety reasons, which proved a key obstacle for Caltrain's plan for electrification. As a pilot project,they are allowing the line to utilize electric multiple units
Caltrain, the San Jose to San Francisco commuter rail line wants to use EMUs where each rail car receives power from overhead catenary wire, as opposed to an electric locomotive hauling the present rolling stock. However, current regulations prohibit the electric multiple units in the corridor. They got their wish.
"Although common in Europe, the smaller electric trains are illegal in the United States because federal officials have long considered them too small, poorly designed and unsafe. But after three years of tests and research, Caltrain will become the first railroad in the nation to use the technology after being granted a waiver.
Caltrain will essentially be a pilot operation for the trains...If successful, commuter railroads and planned high-speed rail networks throughout the nation would have access to cheaper, greener and faster trains.
The waiver allows all passenger trains, whether diesel or electric, to run on the same tracks. Freight locomotives can continue to operate in the wee hours while passenger trains are parked."
Caltrain is pinning its long-time survival on its electrification plan in order to greatly reduce its operating costs.
Thanks to Streetsblog
FULL STORY: Electric train plan granted key waiver

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