Automated Microbus Stations

End-of-Line and Center-Platform Stations are described below. These two types are all that are needed for many applications. It's expected that most Microbus stations would be at grade, rather than elevated.

The end-of-line station is designed to make it easy for vehicles to operate with minimal central control. All collision avoidance functions take place on board the vehicle, and require neither central control nor vehicle-to-vehicle communications.

Paths of arriving vehicles
Paths of departing vehicles
The diagram at the right and the one below it show the paths taken by vehicles entering and leaving the station. It can be seen that arriving vehicles first pull into a corner of the station, and from there travel backwards to their berth. Departing vehicles just pull directly out of their berths. With this layout, several types of conflict can occur. The two most important are: 1) vehicles leaving berths cross the path of those arriving, and 2) departing vehicles from several berths must merge into a single lane. The station layout includes enough space for a departing vehicle to wait between its two conflict points, thus allowing it to deal with them one at a time.

The vehicles are assumed to know their exact location within the station, and to always follow two rules:
  • Departing vehicles yield to arriving ones.

  • When two departing vehicles merge, the one from the berth closer to the exit yields to the other.
These aren't the only possible set of rules, but they allow a vehicle to decide if it should yield based on the location of other vehicles, and not the other vehicle's future behavior. For example, if the rule were that incoming vehicles yield to those leaving berths, it would be necessary for the incoming vehicle to know whether or not a vehicle at a berth was about to leave, since there wouldn't be time to stop after observing a departing vehicle start to move.

Path-crossing conflictThe diagram at the right shows how two vehicles deal with a path crossing conflict. The vehicle in its berth is shown in gray to indicate it's yielding to the other. An on-board sensor has detected an arriving vehicle in the green area, which is the only region of interest in deciding whether or not to leave the berth. Once the green area is clear, the departing vehicle immediately moves across the route used by incoming vehicles. If, by chance, an arriving vehicle enters the far end of the green area a few milliseconds after the departing vehicle has started to move, it doesn't matter. The departing vehicle has committed to leave its berth, and it continues across the path of arriving vehicles and is out of their way in time to avoid a collision.

Since the departing vehicle does not know the future behavior of other vehicles, it will sometimes yield unnecessarily. In the path-crossing diagram above, the departing vehicle about to leave its berth doesn't know whether the arriving one will cross its path, or instead turn immediately into a berth. It has to play it safe and yield in all cases. Since an arriving vehicle never stops until it reaches its berth, this will only cause a few seconds delay.

Merge conflictThe conflict that occurs when departing vehicles merge into a single lane is shown in the diagram to the right. The gray vehicle is yielding because it has detected a vehicle leaving a berth farther from the exit than its own, and that's close enough to the merge point to cause a conflict. As shown, vehicles also have to look in the other direction along the path to the exit, and wait until that region is clear. This results in a safe spacing between vehicles as they leave the station.

In addition to yielding to each other in stations, vehicles must use forward looking sensors at all times to detect foreign objects in their path, and to maintain a safe spacing while traveling between stations.

Automated Microbus center-platform stationThe Center-Platform Station at the right has eight vehicle berths, of which six are occupied. Vehicles are also shown bypassing the station in the outer lanes. Vehicles passing through would slow to 10 mph (16 kph) for ride comfort and safety reasons. The berths are far enough apart that vehicles could enter and leave each one independently, so a delay at one berth wouldn't affect others. Similar designs with more or fewer berths are also feasible.

Passenger areas are shown in gray, and they consist of a pedestrian bridge at the left connected by a ramp to the platform in the middle. Access to the bridge is provided by stairs, and it's accessible to wheelchair users via the ramps at the far left. The bridge would also be used by persons who just want to cross the roadway.

A clearance of 7 ft (2.1 m) is needed for vehicles to pass under the pedestrian bridge. If possible, the Microbus roadway would run in an open cut about 3 ft (0.9 m) deep as it passed under the bridge. The roadway would then rise up to grade level by the time it reached the platform. This would minimize the height of the pedestrian bridge. If it were not possible to depress the roadway, another alternative would be to raise the platform about 3 ft (0.9 m) above grade. Whether or not the vehicles travel in a cut, if they climb a few feet (perhaps a meter) to reach the platform, the height difference between the bridge and the platform can be reduced by the same amount. This, in turn, reduces the length of the ramp that connects the bridge to the platform.

A detailed set of operating procedures for center platform stations has not yet been developed.