Former San Francisco (population 800,000) mayor Gavin Newsom famously rode public transportation only in secret. Compare to Chicago (population 2.7 million) mayor Rahm Emanuel, who’s frequently seen on the “El”.
Unlike Newsom, who supposedly rode SF Muni incognito, Rahm is out in the open, greeting passengers and talking with them. He says he rides the train because it exposes him to people.
Then there’s the political benefit — that’s the primary reason. A lot of people come up and talk to you, and it’s a great way to have people feel like they can access their mayor.
More at Businessweek –> Rahm Emanuel on Upgrading Chicago’s Infrastructure.