Can a US citizen cross the CBX without a passport?

Excuse me, could you please clarify something for me? I've come across a statement that suggests a US citizen might be able to cross the CBX, which I understand to be the Cross Border Xpress facility connecting the US and Mexico at the Tijuana International Airport, without a passport. Is this true? I've always been under the impression that a valid passport is a mandatory requirement for crossing international borders, especially given the heightened security measures in place these days. Could you elaborate on the circumstances under which a US citizen might be able to traverse the CBX without a passport, or if this is indeed a misconception? Thank you for your time and assistance.