Along with several other manufacturers, Sony has a line of noise-canceling 'phones. Sleek and portable, they fold up and stow in a small faux-leather pouch. A single AAA battery will power them for several dozen hours of listening, and they can also be used without the noise cancellation if the battery dies. As regular headphones, they sound pretty good, although not as good as Grado SR-60s costing less than half as much. People next to you sound like they're several feet away.
Traffic noise recedes into the background.
Every once in a while, the headphones can't quite keep up with the external racket and there's an odd, unpleasant throbbing as they struggle to keep the world at bay. Sony really blew it with the cord which comes in two parts. You'd be better off getting one of Sony's fine closed-ear models that block out some external noise, have better sound and cost significantly less.