Express bus service is important for serving areas of fairly high population, but not enough population to justify monorail service. Also, express bus service is quick to deply, fairly inexpensive, and very flexible, and can also be used prior to building of a monorail, and for more distance areas where a monorail would be too expensive to build. The main disadvantage of any bus service is that buses can be delayed in traffic just like any other road vehicle.

A special, more elaborate form of express bus service is bus rapid transit (BRT), where buses may have there own lanes or roadways so they can operate at higher speed, and the system may have other features to provide faster and better service more like a subway or light rail.