Letter to the Editor—Note on a Criterion for Head-of-the-Line Priority Expressway Merging for Buses

Suppose that an expressway on-ramp is two lanes wide up to some point (“merge” point) and then narrows to one lane at the ramp nose. The priority scheme is to give exclusive use of the left lane of the ramp to buses, and to give buses priority right-of-way at the merge point. Assume that buses and cars arrive independently and Poissonwise. Well-known results about priority queues show that this priority scheme is preferable to the standard nonpriority scheme if the ratio of expected ramp delay times for buses and cars is less than the ratio of average “cost” per vehicle per unit delay time.