the ntsb is looking at the signals and mechanisms involved. they are saying the key component is speed. they say the train was going twice the rate of speed it should have been going at that section of the track. at that curve, the limit was 50 miles an hour. another thing they are telling us this section of the track near philadelphia did not have positive train controls. that is an expensive piece of technology but mandated by congress to be placed on all rail lines in the united states by the end of 2015. it was not placed in this section of the track near philadelphia. what is positive train control? an automatic override system. designed to warn the engineer. if the engineer does not heed the warning, the computer system on the train kicks in and stops the train. that was not placed in the