THREE FOR THE ROAD begs for movement but doesn't get it from unimaginative director B.W.L. Norton. Paul Tracy (Charlie Sheen) is the ambitious junior aide to Senator Kitteridge (Raymond J. Barry) and doesn't question his mentor's slippery machinations. Kitteridge asks Tracy to drive his troubled teenage daughter, Robin (Kerri Green), to a Southern psychiatric clinic so that she won't cause him embarrassment in an upcoming political campaign. Tracy blithely accepts the assignment and takes off with Robin and his friend Tommy (Alan Ruck). The two are plagued by the antics of Robin, who keeps trying to escape from them. There's not much to this empty-headed feature except that Sheen gives a commendable performance with what little characterization is provided by the lame script.