Personal Rapid Transit in Stockholm: Market Demand and Economic Viability

· The track should not be larger or more expensive than what is needed. The track cost increases with the weight of the vehicle. One has to distribute the weight. A car with 4 passengers every second gives the same capacity as a traditional train every 15-minute with 1,800 seats.

· The stations should be short. This will be possible with a constant turnover of vehicles and travelers, i.e. dense departures with small vehicles.

· If the vehicle is driven automatically, the only reason for large-scale vehicles falls short. The passenger service governs the traffic performance, not the driver cost. Small vehicles demands a very dense traffic, which means that vehicles are not allowed to stop for boarding and alighting on the main track from capacity reasons. Also, unnecessary stops for service reasons should be avoided. Therefore, all PRT systems are designed with stations located on sidetracks.

· Short time slots between vehicles do not allow switches on the track; this would be too time-consuming. Instead the vehicle chooses its route through fixed switches.

· Acceleration and deceleration does not allow standing passengers. Therefore the system is designed to carry seated passengers only. Guaranteed seating capacity also contributes to the attractiveness of the system. Wheel-chair passengers are foreseen to be able to travel in all PRT-vehicles.

· A PRT ride without a stop between origin and destination station is not only comfortable and convenient. The energy consumption is less than one fourth of that of an automobile.

2. The long-term evolution of auto and transit traffic

Transek Consultants was commissioned by the Office of Regional Planning and Urban Transportation at the Stockholm County Council to investigate the long-term evolution of auto and transit traffic (see Ref. 1, 2, 3 and 4). The estimated auto traffic production in terms of vehicle-kilometers has increased by 88 % between 1970 and 1995 or by 2,5 % annually. The corresponding transit ridership (estimated through ticket sales records) is estimated to have increased by 18 % or by 0,7 % annually between 1973 and 1997. The imbalance of modal development - both in the retrospective and in the forthcoming period is shown in Figure 1.

Our conclusion from this observation is that the present type of transit systems (bus, metro and commuter rail) is insufficient in its performance to attract new travelers to cope with the self-service system of the automobile. There is a strong need for a high-quality performance transit system - such as PRT - if the urban transportation problems of too low efficiency, too high accident rates and environmental air pollution should be curbed.

3. PRT in Stockholm - an efficient and sustainable transport system

The purpose of this chapter is to illustrate the area-wide potential of a high-level-of-service transit system in terms of generalized travel times and market shares - in comparison to the more traditional transit modes, such as bus, commuter rail and subway. A second purpose of this exercise is to form a basis for the selection of the best site for a PRT demonstration track in the Stockholm Region. Therefore, a PRT trip demand analysis has been carried out for the entire Stockholm County Area (population; 1,775,000 inhabitants in 1998), with the simplified assumption that a PRT-station would be (theoretically) available in every traffic zone (1,043 zones) and running on the present major road links in the network. The existing transit modes are assumed to prevail. The demand procedure is summarised in Figure 2.

This formed a basis for considerations of the best suitable location for a PRT demonstration track.

The major changes in the generalized travel times that could be achieved by the PRT system, are mostly a dramatically reduction in the waiting and transfer times, compared to the present day modes of mass transit.

As the PRT system operates as an automated and a demand responsive system, the time spent waiting for the vehicles, does not differ at all between peak and off-peak time periods; this being the opposite for today's' manually driven fixed line service. Thus, the major travel time gains with PRT will occur during the off-peak period. The weighted generalized time (see Footnote 1) is calculated to be reduced from almost one hour (55 minutes) in the base scenario to a little more than a half-hour in the PRT scenario (see Figure 3).

If an area-wide PRT system would be introduced in all Stockholm region, a substantial modal shift from the auto mode (-4 % units) would occur; also a slight shift from the walk and bike modes towards the transit modes, including the new areawide PRT system. The transit modal split is estimated to augment from 46 to 52 % by the new PRT system, i.e. a 13 % growth in market share (see Figure 4).

The number of auto trips is calculated to be reduced by 9 % in the peak period, with its dramatic and positive impacts in terms of reduced congestion, air pollution and road traffic accidents. Transit trips - including the new PRT mode - is forecast to expand by almost one third (31%) during all day, and by 41 % in the off-peak period (see Figure 5).

4. The demand for PRT-trips in the Akalla - Kista area

The choice of the most suitable location for a potential PRT demonstration track is based on at least six various criteria:

• Areas (in fact origin-destination pairs) with a generalized time elasticity with respect to the demand for transit trips(numerically) above -2.0 and a minimum number of transit trips· Areas with a travel time relationship between the transit and auto mode of three or more and a minimum number of transit trips
• Areas with an even distribution of peak and off-peak trips and a minimum number of transit trips
• Areas with a high traffic load and a minimum number of transit trips
• Areas with a high load of estimated PRT trips per track-kilometer
• Robust areas with a combination of high densities in the number of (1) occupied residents per square kilometer, (2) work-places per square kilometer, (3) household income potential per square kilometer and (4) privately owned autos per square kilometer.