No the section a train is on is automatically and mechanically secured by the lights on the section ahead and afterwards. (2 sections if you count the yellow warning lights)
Unless they are operating a dynamic block system like the channel tunnel lines and other high speed lines across Europe. Anything that runs over 125mph (or has to mix with traffic which does) isn't using block signalling.
True dynamic block ("moving block") still isn't that widespread, at least as far main line railways are concerned. High-speed lines are still by far and large using fixed block signalling with conventional train detection (track circuits or axle counters), it's just that the movement authority is given via some sort of cab signalling.