Originally Posted by
dh01
US citizens can be processed at any line, it is only non-US citizens who MUST use the designated lines, presumably because the Immigration agents there are trained somewhat differently.
I've taken non-US persons through the US citizens line so many times without issue that such experiences cast doubt upon any claim that non-US citizens must use the designated lines for non-US citizens. Sometimes it is necessary for reasons of training and/or equipment or something else, but it's neither always nor even generally necessary.