Platooning in FlyWay®

A fail-safe method to make things worse than they already are, is to claim that they are worse than they are.

latooning is by definition the technique of coupling 2 or more vehicles together electronically to form a train. This means that the total headway for vehicles going in the same direction could be reduced, and the capacity of the network would consequently be increased. In synchronous and point-synchronous systems, the cars would essentially be travelling in the same timeslot, although one would have to allow for the fact that the timeslot needs to be longer. The cars in a normal train are also an example of "platooning", although they are mechanically coupled. But mechanical coupling means a huge amount of live energy that has to be built up, and then expended when braking. For a number of reasons, we want to avoid this in the beamcarried automatic systems.		Is platooning really such a good idea? Does the increase in complexity justify the gain in transport capacity? We won´t go into technicalities on this page, just take a look at how we would do it, and what might be gained from it. On this page we will look at: General How much would we gain by platooning? How would we implement this?

1. General

ow much transport capacity would we really gain by platooning? As can be seen from figure 2:1, we have to keep safety distances (D) between the beamcars. These distances consist of 4 components, as explained in detail on another webpage. The relative sizes of these components (at moderate speed) are shown in figure 2:2. They are: the beamcar´s reaction time, before it starts braking the distance covered before the beamcar is brought to a standstil the "jerk-factor", which is a measure of the change in the rate of retardation (can usually be ignored) the length of the beamcar.	Let´s assume that we want to platoon the cars 2, 3 and 4 in figure 2:3. It would then look like in figure 2:4. We would end up with a distance D that is nearly 1/3 of the sum of those distances (D) in figure 2:3, but not quite. We have to allow for the length of the cars, as well as 2-5 meters of space between them (maybe more). In figure 2:4, we have assumed length-of-car = 6m. and distance = 5 m, giving 6+5=11 meters, center-to-center. Checking the listing above, we realize that reaction time and jerk-factor would remain the same, platooning or not. But what about braking distance? Heavier vehicles need longer distances to stop, right? No, not in this case. The 3 cars are individually propelled and individually braked. Granted, though, that 3 cars braking on simultaneously on the same beam segment would tripple the longitudinal strain on the beam supports. So, figure figure 2:4 pretty much reflects the reality.	Figure 2:1 Figure 2:2

Figure 2:3

Figure 2:4

Figure 2:5

o where does this lead? Well, let´s assume a safety distance of 60 meters (which we get by increasing the jerk-factor we calculated with on this webpage). We assume that the cars are 6 meters in length and have a distance in between them when platooning of 5 meters. In figure 2:3, we would then have 3*D = 3*60 = 180 meters. For two platooned cars, we get D = 60 + 6 + 5 = 71 meters. In figure 2:4, with three platooned cars, we get: D = 60 + 2(6 + 5) = 82 meters. The time T that passes before the next car passes a point on the beam is = D/v, where D is the distance between the cars, and v is their speed. If we call: T1 = the time between single cars T2 = the time between two groups of two platooned cars.

T3 = the time between two groups of three platooned cars (as in figure 2:5). T4 = the time between two groups of four platooned cars. and so on, and assuming the same number of passengers (or the same amount of goods) in all cars, and that all such cars and groups keep the same speed, we get an increase in capacity corresponding to 1/T1 versus 1/T2, 1/T3, 1/T4 and so on, where: T1 = 60/v; time between single cars T2 = 71/v; time between two groups of two platooned cars. T3 = 82/v; time between two groups of three platooned cars.

T4 = 93/v, etc. Taken as percentage of single cars, we get an increased capacity of: (2*60 - 71)/71; for groups of two platooned cars i.e. (120 - 71)/71 = 49/71 = 69% (3*60 - 82)/82; for groups of three platooned cars i.e. (180 - 82)/82 = 98/82 = 119% (4*60 - 93)/93; for groups of four platooned cars i.e. (240 - 93)/93 = 147/71 = 158%, etc. One can thus see that platooning 2 vehicles could be very profitable, with an ever growing gain the more vehicles that are connected together in this fashion.

he questions are really: When would we implement platooning? How would we implement platooning? As to when; there are certain places in a network that could turn into bottlenecks at certain times. Obvious such places are after weaving points. The idea is that, when the computer in charge receives the information that the capacity on a certain beam segment cannot handle the load in a normal fashion, and when the load (in the shape of queues) have reached a certain size, then platooning along the bottleneck segment would commense. When the queues have disappeared, platooning would be discontinued. Figure 3:1

Thus considering figure 3:1, it is obvious that the sector denoted A could be quite a bottleneck, causing queues to spill over into all the converging arms. If platooning section A does not solve the problem at hand, the computer could extend the area for platooning up to points B and C. The network has to handle the the cars that are coupled together as one beamcar. The simpler parts of this would include: assigning the cars A and B to the same timeslot at the weaving point (figure 3:2), and henceforth treat them as one vehicle C. Figure 3:2

treat the "beamcar" C as an individual car with the length it actually has when travelling. This length would be the sum of the individual cars, plus the spaces they keep between them when travelling. The trickier part of this handling are of programming nature. These tasks have to be solved: assigning a temporary identity for the combined "car" making and keeping a logical connection between this car and the cars that participate knowing when the new car (.ie. the platoon) cease to exist, either because: the cars in the platoon are going in different directions, such as at point D or one or more cars are stopping at a berth, or the platoon has passed the bottleneck, and platooning is no longer needed assigning a timeslot that fits the size of the platoon (creating and handling timeslots with varying sizes is naturally trickier than handling timeslots having a standard size) the cars in the platoon have to be aware of their temporary identity, and handle their communications accordingly. For technical details about how weaving nodes handle platooning in FlyWay, read this chapter. For technical details about how FlyWay´s intelligent vehicles handle platooning, read this chapter.