There are 6 bus bars. Ground, 3 phase, a "Go" signal, and then another one which I assume is used to enable a master RV reset. In the TF pic, you the rail in the middle is just that: a guide rail. The buss bars are to the sides (3 on left, 3 on right.) The bus bars are physically isolated into "zones" (like, a roller coaster.) The ride system's primary way of tracking the vehicles is by detecting the draw between the 3 phase and ground bus bars. When it detects the draw, it knows that there is a vehicle in that particular zone. Spider-man, for example, has a line of proxy sensors mounted under each vehicle. These sensors hit trigger points along the track. Depending on the combination of which sensors are activated at the same time tells that particular vehicle what to do. The ride control system isn't actually talking to the vehicle, the vehicle is more or less "reading" physical checkpoints along the track. The vehicle is completely inpedendent. The only signal it's getting from control is the "go" signal that the one bus bar provides. This enables the vehicle to move. The green proxy sensors are connected to ride control. They are used mostly for show control during the ride portion, and areas where the vehicles will be parking like the station area and elevators.
If you look on Spider-man's main track layout, the system doesn't have any idea where car #12 is, it only knows which zones are occupied. Then the system knows which zones can get a "Go" signal. The only time ride control actually talks to the vehicle is in special curcumstances, such as RV resets.
The above information mostly applies to Spider-man, but the majority of it can apply to Forbidden Journey as well, even though the control system operates a bit different. FJ vehicles and ride control need to talk to each other when a vehicle is tagged for ADA load, for example. The system pretty much has to know which particular vehicle is where in order to know when to change the switch tracks and whatnot. My best guess is that there are RFID tags on the track under the black cover between the rail an the wheel running surface. Since the vehicle probably needs to know where it is a lot more often than a ride like Spider-man, a line of proxy sensors under each car would be impractical. We also know that this ride uses RFID tags for the restraints already, so I wouldn't be surprised to find it on the track also. It is also my best guess that there is an RFID tag under each vehicle that identifies it. At certain points along the track (like just before the switch approaching unload) there is likely an RFID reader that reads the car numbers. So if RV 17 is tagged for ADA, it knows to send it to ADA load.
Look at the central rail. You will see two wheels pinching it. There is also another set towards the front. These are the drive tires on the vehicle and they also dub as guide wheels. The 4 legs keep the vehicle from tipping over. Spidey's vehicles are so wide and low enough that they wont tip over.
Hope this helps!