PRT Consulting

The Morgantown PRT system which has been operating in Morgantown West Virginia since 1975 is actually a group rapid transit system (GRT). GRT systems have larger vehicles and passengers are typically required to share rides with others going to the same destination(s). These vehicles also typically accommodate standees thereby fitting more passengers into a smaller space. As accustomed as we are to large trains and buses, many believe that larger GRT vehicles make more sense than smaller personal rapid transit (PRT) vehicles. But do they?

Morgantown PRT

The answer is not simple. It depends on many factors. Larger vehicles require larger stations and more substantial guideways. Thus, the capital costs can be higher. The operating savings resulting from carrying more passengers in fewer vehicles can be offset by the additional cost of running larger empty vehicles during off-peak periods.

Because of the standees, GRT vehicles cannot accelerate or decelerate as quickly as PRT vehicles can. This requires greater separation (headway, or time between vehicles) in order to meet the same safety criteria. This in turn means that GRT’s capacity gains are less than would be expected by just comparing vehicle capacities.

2getthere GRT

GRT cannot match the high level of service of PRT where everyone gets a seat, nobody waits for more than about a minute and trips are nonstop. With GRT, seats are in relatively short supply. Passengers have to wait (typically up to about five minutes) for other passengers to fill the vehicle. In addition each vehicle may make a number of stops along the way.

The requirement for GRT vehicles to wait for passengers to arrive who all share the same destination(s) means that GRT does not function very well when there are numerous stations in a system. Either the wait times get quite long or most vehicles are nowhere near full.

Nonetheless, GRT can carry more passengers per hour along a guideway. Increased guideway capacity can be a useful attribute for a networked PRT system where there is intense demand between a few station pairs, but the majority of the demand can be handled by PRT vehicles. In this scenario, GRT service between the busy station pairs can be integrated with PRT service elsewhere. If the GRT vehicles can run on the PRT track, it could be feasible to intermingle the vehicles, changing the fleet mix to meet demand fluctuations. Vectus is developing a GRT vehicle that will run on their PRT track. Another solution that could achieve a similar result could be to platoon PRT vehicles together (either physically or electronically). Forming and breaking the platoons in stations could eliminate safety issues associated with doing so on the fly.

Personal rapid transit systems may be well advised to develop ride sharing/platooning/GRT options to meet the capacity demands that are bound to arise as applications become larger and more diverse. Some may bemoan the need to sacrifice some of the “personal” aspects but, in many countries, the demand for mass transportation will predominate. The distinction between PRT and GRT may become blurred.