As of tonight's site update, two types of comments are now supported.
1) as before, a full line starting with '#' is ignored silently by the site update process
Example:
# The entries below are for my trip to Mongolia:
2) a valid line with four fields can have additional fields (where a "field" is a word separated from its neighboring words by whitespace) and additional fields beyond the 4 will be ignored silently if the fifth (overall) field starts with a '#'.
Examples:
NY NY5 NY67_W NY30/67 # this was probably my first clinched highway segment
NY NY5 NY67_W NY30/67 #there has to be a space before the # but everything after is ignored