Amtrak locomotives must not have very efficient air dryers. Air line freeze ups are due to water contamination in the air system. In exceptionally cold weather we used to be able to add an alcohol based solution to a container on the air compressor that would eliminate any remaining moisture in the air system that the air dryers and blow downs missed. We also made a point of using those air hose holders that plug the glad hands (to keep the snow out of unused hoses) and also blew out the air lines before we connected them. Never had any air problems in sub zero weather. I guess if Amtrak has any doubts it's better safe than sorry, but....