I can tell you that here in Denver, most crosswalk buttons do work. (No, they don't immediately change the light, but they trigger a "walk mode" in the signal control computer that alters the next light cycle, typically giving you a walk signal with a slightly longer light to provide time to get across.)
However, downtown most of the lights are constantly in "walk mode" (including the wonderful "Denver shuffle" - http://www.urbandictionary.com/define.php?term=denver%20shuffle ), so in this part of town there are no buttons to push.
Some of the newest traffic signals around town in fact have an audible indicator (a sort of "thunk" sound) and a red light that comes on in the middle of the walk button when it's been activated, so if you're approaching an intersection to cross, you don't have to wonder or go pressing the button 15 times just in case.
However, downtown most of the lights are constantly in "walk mode" (including the wonderful "Denver shuffle" - http://www.urbandictionary.com/define.php?term=denver%20shuffle ), so in this part of town there are no buttons to push.
Some of the newest traffic signals around town in fact have an audible indicator (a sort of "thunk" sound) and a red light that comes on in the middle of the walk button when it's been activated, so if you're approaching an intersection to cross, you don't have to wonder or go pressing the button 15 times just in case.