Palle R Jensen, RUF International
The traffic systems of big cities are under a huge stress. The demands are much higher than the capacity. This has been proven again and again. Whenever a new road is build, it is very rapidly filled up with new traffic.
What happens if a dualmode system is implemented in a growing city?
It can go terribly wrong. If it is not planned carefully, the dualmode system could add to the problems instead of solving them. The relevant question must be:
How should a dualmode system be planned in order to solve more problems than it creates?
One of the major problems with a high capacity dualmode system is the problem of egress. Access can be controlled. Vehicles are not allowed access before an empty slot appears on the line. When they want to leave a few minutes later at a desired exit, the situation at that exit may be problematic. If the road network is not able to absorb the vehicle flow from an egress ramp, the system has a problem.
In the following I will try to explain how this problem can be minimized. The examples are from the RUF system (www.ruf.dk/egress).
The Nature of the Problem
The problem is basically that a dualmode system consists of a high capacity network of guideways plus a low capacity road network. If all vehicles from the high capacity network were allowed to leave at one exit, it could easily create problems. The road network plus the highway system has been created gradually over a long period. Every time a bit of road has changed it has usually created problems which then were solved either technically or by the users adjusting their behavior.
This gradual approach is difficult with a true dualmode system where both vehicles and infrastructure are special. This chicken and egg problem can be solved by introducing the dualmode system as a public transport system from the start (using busses and public cars). It will then be possible to gradually create a network of guideways for public transport. At that time it will become extremely attractive for a car owner to be able to use the guideway instead of congested highways. People will demand dualmode cars (ruf) and the car manufacturers will make them.
This new network can work between stations without any problems, but if the dualmode principle is to be used to its full potential, the road network will have to be included. This means that dualmode busses (maxi-ruf) must be run in a dial-a-bus mode in order to bring passengers to the automated part of the system. It also means that dualmode cars (ruf) drives from door-to-door using the rail network for the long distance high speed part of the trip. Both types of vehicles will have to be able to egress from the monorail network without problems.
One solution to the potential problem with street congestion at egress is obviously to allow for more exits. If the traffic flow is divided into several independent flows each going to an exit, it will be possible to prevent problems. The exits should be placed as far from the junction as is economical while also considering allowable visual impacts.
Switch with Multiple Directions
For this solution to be realistic it is very important that the switch is able to handle more than 2 directions. A normal train switch is only able to be set in one of two positions. Most system developers seem to adopt this philosophy. In the RUF system, the switch has been created differently. The vehicles are guided through the switch at low speed (20 mph) using magnetic fields at different frequencies. The fields are present all the time and the vehicle decides which frequency it will follow. It works like a radio. When a radio station is selected, the radio only listenes to its frequency even if all the frequencies are present at the antenna all the time.
The RUF switch magnetic fields works like electronic rails and it is easy to have several frequencies to choose among. In a realistic scenario the switch could make the ruf drive in one of 4 directions and consequently use one of 4 exits. The risk that all 4 are stopped by congestion is minimal if they are spread out in the area around the junction.
If all exits are blocked, the ruf may experience a "wave-off". This means that the system knows that all exits are blocked and that it is impossible to get off. This would be a big problem if it was happening for a train or for a PRT system. You would be forced to walk from a station that was a long distance from your destination. In a dualmode system, a "wave-off" is not a big problem. It would mean that you would exit the system at a nearby exit and drive back to your destination. It would still be door-to- door transport but it would take a little longer time.
Another important factor which can be used to minimize egress problems is the planning of the network. If the network is placed on top of an existing highway system and with the exits near to the highway exits, the two systems together could create too much traffic to be absorbed by the road network.
A better strategy is to design the network to complement the highway system and place exits as far from the highway exits as possible. In a city like Los Angeles, many of the arterial streets are wide enough to host a bidirectional guideway. Since many of them are completely straight, they would be ideal for a system of silent high-speed electric cars and busses. Both congestion problems and pollution problems could be solved with this system and travel time would be short, predictable and productive at the option of the user.
A very interesting solution to the egress problem is to place "flow absorbers" like supermarkets or parking facilities close to junctions. Maybe it would even be possible for junctions to be privately owned such that a big mall could make it very easy to leave the guideway network at their junction, park and go shopping on the way home. The junction could be integrated into the building (no problem with electric cars) and on-line shopping could become very attractive. Imagine that you use the time from your work to your own residence to make a selection of daily goods via your computerscreen while you move towards the junction where you want to get off. When you arrive, the bag of goods is ready at the fast counter and you pick it up without even leaving your vehicle. You have paid in advance, electronically.
The nearby parking facility works as a buffer in case of problems. If you cannot use the streets because of congestion, the supermarket will be happy to make sure that the waiting time becomes interesting and tempting.
Major Activity Centers
Many places like sports arenas, exhibition halls etc. have nearby parking facilities which will work perfectly as buffers for the traffic flow in case of temporary problems.
At the same time it will be very wise to connect MACs to the network in order to get fast access to the center and to be able to empty it quickly.
Automated Parking Facilities
Near the center of a city, a dualmode system can use the automated mode in a very favourable manner. It will be possible to drive to a destination using the ruf in PRT mode. This means that it will use a fine meshed network covering the central part of the city. Along the guideway there will be frequent off-line stations where people can get off. These stations could even be part of office buildings, so that the user will enter the building at second floor directly. This may be very attractive for security reasons and for people who want privacy.
If the vehicle is a dualmode car, it can now continue by itself and drive empty to the nearest automated parking facility. It will have its own IP adress so it can be contacted whenever necessary. This way there will be no egress problem at all.
It will be possible to plan a dualmode system in such a way that egress problems can be handled such that the system will be experienced as an improvement both for the users and for the overall congestion level in the city.
Last modified: August 01, 2001