Personal rapid transit

An ULTra Vehicle. Photo by Magnus Manske

Introduction

Personal rapid transit (PRT) is being touted as an alternative to more expensive heavy rail, light rail (LRT), and bus rapid transit (BRT) modes. PRTs share characteristics with people movers, there are grade separated and automated. They are also similar to taxis in being smaller in size than traditional transit vehicles and can take passengers directly from trip origin to destination without stopping between and with shorter wait times and fewer transfers. Though they operate over fixed routes they can bypass stations and can be part of a denser network of stops that can provide more convenient locations for passenger access than traditional fixed rail systems. Due to their smaller vehicle size, typically carrying 4 or 6 passengers though larger capacity vehicle can be used, the stations can be smaller and less expensive to build. Though they are slower moving and carry fewer passengers per car, because they can operate on reduced headways, over larger areas, and at higher average speeds they are capable of passenger throughputs similar to other rail modes.

Advantages and Disadvantages

Compared to steel wheeled and diesel powered transit vehicles, PRT are quieter and more energy efficient since they operate on rubber tires and are powered by electricity. The are also potentially safer since the vehicles are lighter than LRTs and run on dedicated guideways. They also take up less land for stations and right-of-way though this may be less so with greater network coverage. On the down side, PRT systems require a larger number of vehicles than other modes which could increase maintenance and replacement costs. As they are entirely grade separated they may also require more elevated sections of track with their accompanying aesthetic concerns. A recent study proposing a PRT alternative to the planned Purple Line light rail or BRT system in Maryland concluded that PRT would save millions of dollars in construction and operating costs, while reducing wait times, improving safety, and potentially serving a wider area.

Variations

Technological advancements in the area of driverless vehicles suggest variants on the PRT model that could operate outside of guideways in ordinary traffic. An autonomous taxi network (ATN) based on PRT principles could have numerous stations located on the grid each within a few minutes walk of large numbers of possible passengers. Rides could depart as soon as two or more passenger arrive at a taxi stand. An even more aggressive approach based on the "smart paratransit" or SPT model, could pick up passengers directly at their trip origin eliminating the need for them to walk to a central location.

Further Reading

Reuban Juster and Paul Schonfeld, "Comparative Analysis of Personal Rapid Transit as an Urban Transportation Mode," Transportation Research Record No. 2350, 2013, pp. 128-135.

This research report examines the potential of personal rapid transit (PRT) as a substitute for traditional medium or large-scale bus rapid transit, light rail transit, and streetcars using the proposed Purple Line light rail project in the Maryland as a case study. The study finds that the PRT option performed best in total travel times and capital costs indicating that PRT could be a viable transportation mode in other urban environments.

Chris Brownell and Alain Kornhauser, "A Driverless Alternative: Fleet Size and Cost Requirements for a Statewide Autonomous Taxi Network in New Jersey," Transportation Research Record No, 2416, 2014, pp. 73-81.

This paper examines the potential for an autonomous taxi network (ATN) based on transit criteria that include (a) congestion relief, (b) safety,(c) lesser, environmental impact, (d) economic feasibility, and (e) comfort and convenience. Two potential designs for an ATN are presented based on the classic personal rapid transit (PRT) model as well as the idea of smart paratransit (SPT) and compared with one another in view of statewide transportation demand in New Jersey. The SPT model is shown to be the more economically viable option.