Currently the hotkey to change your characters running speed is Ctrl + R. This command causes your running speed to cycle one step forward (from walking to running for example), but also cycles back to a slower speed if no faster speed is available. This can cause problems, for example when in a pinch and forced to run, the player might spam the Ctrl + R command one time too many, causing his character to go into crawl speed instead of sprinting, a potentially fatal mistake.
My suggestion to solve this is to have two hotkeys, one for increasing your run speed by one step, and one for lowering it by one step. With this setup, a stressed player could spam the "go faster" hotkey to start sprinting, without fear of accidentally setting his speed to "crawl".