  Transit vehicles operating under skip-stop service visit only a subset of the
stops residing along a corridor. It is a strategy commonly used to increase
vehicle speeds and reduce patron travel times. The present paper develops a
continuous approximation model to optimally design a select form of skip-stop
service, termed AB-type service. The model accounts for spatially-heterogeneous
demand patterns. An efficient heuristic is developed to obtain solutions. These
are shown to be near-optimal for a variety of numerical examples. Results also
indicate that optimal AB-type designs outperform optimized all-stop service in
a variety of cases. The AB-type service is found to be especially competitive
when travel demands are high, trip origins are unevenly distributed along a
corridor, and patrons have relatively high values of time. In these cases,
AB-type service is found to reduce system costs by as much as 8%.
