Riding public transport has been around for over 100 years
The New York City Subway was built in 1905, the London Underground is older than that.
Warsaw had a tram (Trolley) from around the year 1900
So its clear this is not a new issue, Its clear The Chofetz Chaim, Rav Chaim Ozer etc all knew about riding on a vehicle with members of the opposite gender. Did any of them ban it?