As anyone who works in Midtown Manhattan or the Upper East Side can testify, gridlock awaits the locals every year at this season when the United Nations General Assembly meets. Streets are blocked, and traffic is halted for motorcades. Prime ministers and presidents shuttle from place to place. Having a limo and driver doesn’t help in the struggle to get to the office. Hence Steve Schwarzman took the subway this week … and the firm tweeted a photo of the CEO on the 6 train, which runs down Lexington Avenue, by the back door to Blackstone’s office.