PRT - Hermes
Technical issues
What will happen if power goes down?
What will happen in case of a malfunction?
What will happen if the vehicle is overweight?
Why the vehicle can only seat 2 persons?
How realistic and reliable is the simulation?
What will happen if power goes down?
Vehicles will be equipped with batteries large enough to allow them to move , at a lower speed , for 1-3 km. In case of a power outage they will manage to reach the next station (not the correct destination station) and passengers will get out.
What will happen in case of a malfunction?
First of all we must note that this will be very rare since all critical subsystems will be redundant.
However if something does break , that doesn't mean that the whole network will stop working: A broken station will force passengers to disembark to a nearby station (500-600 meters away). A problematic guideway segment will force vehicles to take alternative routes.
Obviously passengers of a malfunctioned vehicle will experience considerable delays. All the others however shouldn't have any problems.
The network's behavior at faults will be something like the Internet's behavior in similar cases: A broken server may disrupt the connection of those computers that use this particular server to connect to the internet. The rest of the network however works normally.
This is very important indeed: We can use the methodologies , algorithms and even hardware (cables , switches , routers) that are already commercially available . This wasn't the case 20-30 years ago when the first PRT systems were under study.
What will happen if the vehicle is overweight?
There will be a sensor continuously measuring the cabin's weight. If the passengers and their luggage weigh too much , the vehicle won't leave and an appropriate message will be anounced through the vehicle's speakers.
Why the vehicle can only seat 2 persons?
Lets assume that the vehicle is bigger , seating 4 passengers. Now a big group , let's say 4 friends can travel together. However , when we travel alone , isn't it a waste of energy to carry with us 3 empty seats? Experience shows that a group of 1-2 persons is far more usual than a group of 3-4. A big vehicle is not economic.
Therefore the vehicles can seat only 2. If there is a group of 3-4 persons they can easily use 2 vehicles: the station
has as many vehicles as we want.
Cars could be more economic if they were smaller too. But when there is a group of 3-5 people what can you do?
You won't have as many cars and drivers as you want. Therefore cars are bigger , able to seat 4-5 people , in order
to cope with this , rare , occasion.
Well it's not exactly tiny: Seats are as comfortable as car seats. A passenger can place lugagge in front of him.
However the target is to make the vehicle as short as possible (about 2 meters) This way stations and storage depots will be shorter too.
The vehicle must not be very wide: (about 1-1.2 meters). This means smaller depots and guideways (important!) , with smaller visual obtrusion.
The vehicle must not be veray tall (no more than 1.7 meters including the bogie) Hermes network will have 2-level crossings and we'd like the clearance to be as small as possible.
The vehicle must be light: Guideways will be lighter and cheaper.
In a few words Hermes will be as small as practical in order to service 99% of the trips. For the rest 1% (e.g. if you want to carry something big and heavy) you can use a taxi.
How realistic and reliable is the simulation?
Simulation is a very important tool. It helps engineers to investigate advantages/disadvantages of a system befory they even build a prototype of it. For a simulation to be useful it must be close enough to reality.
Obviously a simulation can't describe the real world in every detail. The engineer responsible for it has to make several assumptions. The nature of these assumptions affects the quality of the simulation.
For example in a low quality simulation of a transit system there could be unacceptable things like:
- Vehicles appear/disappear at will
- Vehicles "collide" , meaning the move on top of each other with no consequences
- People appear suddenly in groups of 50 persons or entire groups go to the same destination
- Vehicles accelerate/decelerate too fast
- Passengers embark/disembark in less than a second
On the other hand other assumptions may be ok:
For example rain doesn't affect a rail system so it's no big deal if the simulation deosn't take rain in consideration.
In general , the author has made a considerable affort to avoid all important unrealistic assumptions. A little study on what the simulator presents and common sense is enough to convince someone. Simulator's manual has additional information on that topic. Of course a discussion on the detailed simulation model requires much more space than available in this web page.
Finally we must note that the ability of simulator to handle traffic in a Hermes network is a LOWER BOUND of the ability of a real system: A real system will be more sofisticated and of of course... more expensive than a program freely available on the internet! (that means that currently I have many ideas on how to improve the system.Simulating those however needs massive restructuring of the simulator code)
