If you're busting your butt during a grueling interval or tempo workout, the last thing a runner wants to do—or waste breath on—is to yell "TRACK!" at the walkers taking up the first four lanes.
If a runner is forced to give a shout and the walkers don't move, expect a shoulder thump, or the very least, some exasperated waving and angry mumbling. The same rule applies on a bike path or sidewalk—please respect the runner's right of way.