Dual-Mode Solutions to LRT/PRT Problems

by Palle R Jensen

Note: Persons not familiar with the Danish dual-mode RUF concept can obtain information about it at the RUF Web site .

In the debate between LRT advocates and PRT supporters some potential problems for PRT (and some major problems for LRT) have been raised. The purpose of my contribution to the debate is to discuss whether a Dual-Mode PRT like RUF could solve these problems.

Problem 1:

The network of guideway is expensive, so it requires high capacity in order to justify the investment.

Conventional wisdom tells that people are willing to walk 1/4 mile to a station. If that is true, the guideway and the station network has to be extensive in order to obtain significant ridership. I doubt that it is true. The auto-dominance even in transit oriented cities in Europe prove it to be wrong. People only walk 1/4 mile if they are forced to it (cannot afford/drive a car). This is a huge problem for LRT. It is a much smaller, but still serious problem for PRT especially in dispersed cities like Los Angeles.

Solution 1:

Dual-Mode systems require far less guideway.

A Dual-Mode system using guideway only to substitute the crowded and dangerous highway needs only a small amount of guideway to obtain significant ridership. The riders only have to walk a few meters to the RUF, they use the normal uncongested roads to get to the rail, they avoid highway-congestion, they have privacy, they save energy and don't make noise.

In the RUF Dual-Mode system, where the vehicles "ride" on top of the triangular guideway, the cost and dimensions of the guideway is minimized. This is very important because the guideway cost is the major part of a system cost. It is also important for the acceptance of an elevated guideway. A 1 x 1 m triangular guideway (base x height) is much more acceptable than a 1.78 x 1.70 m PRT 2000 guideway, not to mention an elevated LRT guideway.

Having a guideway network with a large mesh size (3 miles) means that it is possible to create trains with high capacity. Close coupling is relatively easy in a RUF system where the center of gravity, the driving wheels, the rail brake and the coupling unit are all placed along the same horizontal line. The dynamic forces involved, create far less problems than in conventional systems.

The mix of small and large vehicles (2-4 person RUFs and 10 passenger MAXI-RUFs) makes it possible to obtain high capacity where it is relevant. City Center to Airport, between Major Activity Centres, during rush hour, etc. can be matched perfectly using a mixture of RUFs and MAXI-RUFs. The way the RUF guideway is designed, it can be used by a wide range of vehicles.

Problem 2:

The number of empty vehicles in a PRT system can be large in order to offer on-demand service.

In a LRT system with large vehicles, the vehicles are seldomly quite empty. Nevertheless, the average loading factor of LRT systems is often less than 20%. This is probably worse than for the PRT system.

Solution 2a:

Privately owned RUFs don't drive empty (except for automatic parking).

The RUF is meant as a substitute for the car in the city. This means that unlike PRT, many riders will own their vehicle. This part of the system cost is paid for by the users so even if the total investment is larger (more vehicles because private vehicles are not reused as public PRT vehicles are), the investment for the operating company is smaller. A private RUF will follow the owner. He will not normally have to wait for it.

Solution 2b:

Dial-a-RUF service can match the demand optimally.

Using Information Technology is only possible with small vehicles. PRT and

RUF/MAXI-RUF are ideal. LRT vehicles are not.

Problem 3:

Elevated off-line stations need expensive elevators.

Solution 3:

Off-line stations can be at ground level in PRT systems but few are likely to be so located. In a Dual-Mode system, all stations are likely to be at ground level.

Problem 4:

Boarding delays affects all PRTs in a platoon.

The same is true (and much worse) for a LRT system. A problem in one car of the train will block the whole train and the whole line will be blocked.

Solution 4:

In a Dual-Mode system, it is relatively easy to have parallel platforms at off-line stations. The redundancy will be even better than in normal PRT systems. A boarding problem in one MAXI-RUF will not affect the rest of the system.

The platforms could even be organized as normal bus stops. A chauffeur enters the MAXI-RUF when it leaves the main line and drives it to the stopping place. When new passengers have boarded the vehicle, he drives the MAXI-RUF back to the main line where he leaves the vehicle which continues as an Automatic People Mover. One chauffeur can manage many vehicles, so his salary is not a large burden for the operation of thesystem.

Problem 5:

A pulse of passengers can be a problem in a PRT system whereas a LRT system can handle it (if the pulse is syncronized with the train arrival).

Solution 5:

In a RUF system, MAXI-RUFs can be stored at low cost at ground level so that they are ready to be used with very little delay.

Palle R. Jensen is the principal inventor of RUF and works with RUF International in Denmark.

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Last Modified: January 6, 1997