Advanced Transit Systems are comprised of small driverless vehicles operating on dedicated guideways. Stations are offline (on sidings) allowing each trip to be express or nonstop. Small vehicles result in frequent service and allow lightweight, elegant guideways that can be readily retrofitted in existing urban environments. Guideways can be configured in one-way interconnected loops, or they can follow corridors in a more conventional two-way configuration.
The ASCE Automated People Mover Standards defines these systems under the term Automated Transit Networks (ATN). ATN is an umbrella term covering both Personal Rapid Transit (PRT) and Group Rapid Transit (GRT). PRT has smaller vehicles carrying one to about six seated passengers. GRT vehicles carry up to about 25 passengers, seated and standing.
ATN systems are characterized as having switching that requires no track-based moving parts. This allows vehicles to travel close together like cars on a freeway thereby having the potential for relatively high capacity. Onboard switching in turn enables offline stations which are a key differentiator.
Offline stations allow close station spacing without slowing through traffic down. Now we have a system
- Short walking distances due to offline stations
- Short waiting times due to many small vehicles
- Short trip times due to express or nonstop travel
- High capacity due to onboard switching
- Low costs due to small vehicles, few stops, and light infrastructure
This system can leverage the network effect whereby ridership (and revenues) increase faster than costs as stations are added. The potential thus exists for farebox revenues to cover operating and even capital costs once there are enough stations in an urban area. Note that the network effect does not work for buses and trains because adding stops/stations slows down all travel and potentially adds the need for transfers.
The following section, System Comparison, compares the proven capabilities of ATN systems already in public service with the predicted capabilities of systems under active development.