What if it were possible to increase an arterial's traffic capacity by more than would happen by adding a lane each way - but without having to widen it? Miami and Fort Myers, Fla., are both looking into this idea. It's called converting an arterial into a "managed arterial." The basic idea is to give motorists a way to bypass traffic signals, by adding overpasses or underpasses to major arterials. Because those "grade separations" are costly to build, a small toll (e.g., 25 cents) would be charged, electronically, for each underpass a motorist used.