That's what I was thinking. The Agent checking you in will not want to get in trouble, so deny you boardig

My first TWOV started at UA's outpost at DAL (not DFW) where they have 7 or so flights to IAH and 2 to DEN (all express flights, no mainline), and I knew they would be unfamiliar with this, so went to the airport a day early to do 24 hour advance checkin (no way to do this online with UA for this route).

Second TWOV started at DFW, and the Agent immediately started looking for my Chinese visa, looked startled when I told him that I don't have a visa, but was familiar with the rule. I did allow an extra hour just in case @:-)

EmailKid