Why Does RUF Use a Special Guideway?
Palle R Jensen, RUF International
Wouldn’t it be much easier to let the ruf drive as a normal car using the road wheels all the time and obtain the automated mode by adding guidance electronically and/or mechanically?
It might be easier, but not wiser. Let me try to explain why.
The biggest problem with dualmode may not be the technical problems, but the responsibility problems. When the vehicle is in the automated mode, who is responsible when something goes wrong.
I think it has to be the operator, like in a train system.
For that reason, the system needs to be extremely safe.
In my opinion this high level of safety cannot be obtained using the road wheels in the automated mode. A safer principle has to be used.
How can safety be increased?
In order to analyze this, let me first look at several basic principles in transportation dynamics: Lateral guidance, longitudinal distance control and braking abilities.
LATERAL GUIDANCE
When trying to get more capacity out of a given road space, it is tempting to let the vehicles run on a narrow lane using the normal wheels to keep the car on the track. This can be done electronically or mechanically. This will work perfectly as long as no problems appear. However it could easily be disturbed by things like debris on the road surface not to mention snow, ice, rain etc.
The dynamic forces when driving at high speed and hitting some unexpected obstacle could be surprisingly large and make the vehicle jump to the opposite lane unless it is prevented from doing this.
RUF solves this problem using a special drive system (see: http://www.ruf.dk/ruf/p4.htm and http://www.ruf.dk/ruf/p5.htm ) where the vehicle is locked to the guideway by means of wheels pressing against the guideway from both sides. This will make it almost impossible to leave the guideway in any unauthorized way.
The separation of the guideway from the surroundings by means of elevation or underground placement, makes it impossible that animal will get into the path of the vehicle.
LONGITUDINAL GUIDANCE
Distance keeping can be made electronically by means of radar, laser or ultrasound. The problem is that the situation in a platoon of normal cars can become chaotic.
The normal motor + gearbox drive system makes it very difficult to control the speed in a platoon accurately enough. Every car will have its own drive characteristics. It will not change gears exactly the same moment as the others. This disturbance makes it very difficult to manage close distance keeping.
RUF solves this problem in two ways.
Electric propulsion makes it very easy to control speed in a platoon since no gear shift is needed and the motor has a smooth drive characteristic. The battery problem associated with normal electric cars is solved by using power from the guideway to recharge the small batteries needed to get to and from the network of guideways.
RUF uses close coupling of vehicles in a train. It is much simpler to keep the distance of zero than to keep the distance of 2 meters like in the Automated Highway System.
Even a short distance of 10 cm is less problematic, since a dangerous differential speed between to close vehicles cannot build up when only 10 cm is available.
BRAKING ABILITIES
The normal car (and the normal train) has very limited braking abilities. The braking friction depends on how the wheels interact with the surface at the pressure defined by the gravity pulling the vehicle to the ground.
If the vehicle drives fast, aerodynamic forces may lift the vehicle so that this friction will be lowered. The surface quality is also critical. Ice, rain, oil, leaves etc. could limit the braking friction without warning.
RUF has far better braking abilities.
Because of the patented drive system, the drivewheels are able to adjust their pressure against the top of the guideway in order to obtain a greater friction during braking. An aerodynamic lift is no problem. On the contrary, it will decrease the rolling resistance.
The braking surfaces are vertical so rain will not collect on the surfaces. Snow will not pile up around the guideway since it is elevated and leaves will prefer horizontal surfaces.
A special rail brake for emergency braking can put pressure on both sides of the rail and obtain large enough braking friction for emergency braking.
OTHER ASPECTS
There are several other reasons for using a special guideway in stead of the normal road space.
The implementation phase becomes very difficult if you start by taking up some of the precious road space for a new system for modified cars. The result will initially be increased congestion.
RUF uses a completely separated infrastructure in the first phase. When people realize the benefits using this infrastructure it will be possible to convert the road space into rooms for multiple guideways. The result is reduced congestion from the very start.
The switching of vehicles from one automated lane to another is always a critical issue. In my view it is extremely difficult to obtain this function in a road based system with normal cars.
RUF uses a well proven magnetic guidance principle at low speed (20 mph) for the switching. An example of a RUF junction can be seen at www.ruf.dk/rufsim.exe and www.ruf.dk/rufsim.doc.
CONCLUSION
Even if it might seem tempting to realize dualmode using modified normal cars, I am convinced that dualmode can only be successfully implemented using special vehicles and special infrastructure like in the RUF system.
See: www.ruf.dk
Last modified: December 23, 2002