The traffic at quitting time is a bother. Radio station WCAM equips men with binoculars and positions them at strategic overpasses to describe the gnarls and tangles. Lila Mae is never able to differentiate these men from the meandering isolates who linger at the margins of freeways. All of them make obscure, furtive gestures, all share a certain stooped posture that says they lack substantive reasons for being where they are, at the side of the road. Impossible to distinguish a walkie-talkie from a bottle of cheap wine at such distances.
They don't have alibis, Lila Mae appraises the men at the side of the road.
This is from The Intuitionist by Colson Whitehead. I don't understand what does alibi mean in this context. You can see some more text here.