No surprise here. From [1] Reuters, with thanks to Judy:

WASHINGTON, July 7 (Reuters) - The United States is raising the terrorist threat level for rail and mass transit systems, but not for airlines, after the bomb blasts that rocked London, a U.S. government official said on Thursday.

The official said the alert level for trains and subways would be raised to orange, which signifies a high risk of terrorist attack, from yellow, the mid-point on the five-point color-coded system.