emphasized by the fact that

[KLPNO]

Hello everyone
I'd like to ask about the meaning of the phrase "emphasized by the fact that..." in the following context.

Annabella had expected the next day's return trip to be a bit more difficult. After all, people didn't travel between Blue and Yellow that often, for very good reason, and to be let back into a Blue after being in a Yellow required special dispensation -- emphasized by the fact that the train back was even emptier than the train down.

I'm not sure that I understand which word (or phrase) "emphasized by the fact that the train back was even emptier than the train down" refers to.
All I came up with is that 'emptier train' is one more sign of how difficult it is to receive special permission to travel from a Yellow zone to a Blue zone.

[Horsa]

Yes you are right.

The author is saying

1. that not many people travel between blue and yellow.

2. that if you go into yellow from blue, it is hard to get permission to return

3. that this (2) is made very obvious by the fact that trains going to yellow may have few passengers but the trains returning from yellow have even fewer passengers.

[KLPNO]

Yes you are right.

The author is saying

1. that not many people travel between blue and yellow.

2. that if you go into yellow from blue, it is hard to get permission to return

3. that this (2) is made very obvious by the fact that trains going to yellow may have few passengers but the trains returning from yellow have even fewer passengers.

Thank you very much, Horsa!