Jennifer Markowitz directed the first staging of Will Kern's understated dark comedy, and I never understood why the folks at Famous Door didn't hire her to redirect the play whenever the cast changed significantly, as it seemed to do every few months or so. Instead they left this intelligent, honest work, about a hellish day in the life of a beleaguered Chicago cab driver, in the hands of a series of foster directors, some better than others, which meant that the long-running Hellcab has not been consistently excellent. (James Schneider directed a lamentable version of it six months ago that reduced the multilayered tragicomedy to a series of Second City-style comedy blackouts.) But Dan Rivkin--Hellcab's newest stepfather--has had considerable success, fashioning from Kern's script a show by turns dark and funny, with the depth and emotional range I remember from Markowitz's original production. For one thing, Rivkin has packed the cast with actors of the caliber of Laura T. Fisher, Tim Beamish, and Frank Dominelli, who are as comfortable playing comic scenes as serious ones. And at the center of it all is Richard Cotovsky as the put-upon cabdriver, a full if burnt-out human being whose every day on the job is a ride on a roller-coaster. Only the role's originator, Paul Dillon, played the cabbie better. Ivanhoe Theater, 750 W. Wellington, 975-7171. Open run: Fridays-Saturdays, 10 PM; Sundays, 8 PM. $10-$13.