Automated Microbus Control System

The Automated Microbus control system puts almost all the intelligence in the vehicle. The roadway contains only passive markers, and central control is generally limited to routing empties and responding to unplanned events. The design of the on-board control system is greatly simplified by the fact that every vehicle knows the exact configuration of the entire Microbus system.

The on-board control system has three basic functions, which are listed in order of increasing complexity:
  • Individual Vehicle Guidance. Moves the vehicle from origin to destination without concern for other vehicles or unexpected events.

  • Interaction with other Vehicles. Slows or stops as necessary depending on the position and speed of other vehicles.

  • Response to Unplanned Events. Stops the vehicle when necessary in response to unexpected events such as someone trespassing on the exclusive roadway.
In addition, the vehicle must be capable of certain low speed maneuvers which are not part of normal passenger service, such as putting itself in position to tow a disabled vehicle.

Microbus with magnets in center of laneIndividual Vehicle Guidance. Vehicles could be guided by permanent magnets buried every meter (3.3 ft) or so along the center of the lane. This approach was used at the famous 1997 event in San Diego, where automated highway technology was demonstrated to thousands of onlookers (in this writeup there is a photo halfway down the page of two hands holding a magnet and sensor; look closely to see another magnet embedded in the road). Magnets for guidance have been used more recently in the Toyota IMTS driverless bus and other systems. Other technologies, such as following signals from a continuous wire buried along the center of the lane, are also possible.

Each Microbus would know the route to take from every origin to every destination, and initial Microbus systems would be small enough that there would be only one feasible alternative. The individual-vehicle portion of the control system would be responsible for: 1) lateral guidance -- keeping the vehicle in the center of its lane, 2) controlling the motor and brakes so that acceleration/deceleration and jerk (the rate of change of acceleration/deceleration) are within predetermined limits, 3) choosing the correct branch at diverges, and 4) docking precisely at stations so the gap between vehicle and platform is within a preset limit. As a backup to the lateral guidance system, there would be a physical barrier about one foot (0.3 m) high along each side of the lane with a clearance from the vehicle of about 9 inches (23 cm).

Microbus using sensor to maintain separationInteraction between Vehicles. Vehicles in the same lane would maintain separation without central control by using either radar or laser sensors to determine the distance and speed of the vehicle ahead. This technology is currently mass produced for adaptive cruise control in automobiles. It has been available to the general public for high speed travel for several years, and is just being introduced for low speed operation as well. A long-recognized issue with this approach is following a vehicle around a curve. Since the Microbus knows the location and radius of every curve in the system, it will be able to angle its sensor to the right or left as necessary when approaching a curve. The two lanes of the roadway will probably have to be separated slightly through curves, so that a vehicle in the other lane doesn't block the line-of-sight to the vehicle ahead.

Two microbuses mergingIn addition to detecting the vehicle ahead, the on-board control system would handle merging without central control. This task is greatly simplified by giving one branch of every merge permanent priority over the other. Every vehicle will know the priority of each branch in the system, as well as its own location. If it's on a high priority branch, it will continue as if there were no merge. If it's on a low priority branch, it will use its sensors to detect vehicles on the high priority branch, and slow or stop as necessary. The diagram shows a low priority vehicle using a number of narrow-beam sensors, but a single scanning laser could be used instead.

If a vehicle were delayed too long on a low priority branch by a continuous stream of vehicles on the other branch, the central control system could direct a high priority vehicle to stop for a few seconds to create an opening. However this would not be a vital control function. If the high priority vehicle didn't get the message to stop, no accident would occur. The waiting vehicle would just experience additional delay.

Child running across Microbus roadwayResponse to unplanned events. The most difficult function of the control system is to respond to unexpected events. It's proposed that the fences isolating the Microbus roadway be about 4 ft (1.2 m) high. This will prevent anyone from inadvertently entering the roadway, and should be an effective barrier against very young children. In many situations, a 4 ft barrier is considered appropriate to protect the public from serious hazards, such as falling from a high balcony. Nevertheless, it must be recognized that adults and older children will be able to climb the Microbus' isolation fence if they choose (certain parts of the system, such as areas near stations, may require a higher fence.) The on-board control system must detect trespassers on the roadway, and should be able to detect someone in the act of climbing the fence. The on-board system must also detect an object on the roadway, such as a fallen tree limb.

Because it's assumed the entire Microbus system is completely known to every vehicle, it would be possible to take sensor readings and/or computer vision images in advance every foot (0.3 m) or so along the roadway. During operation, vehicles could compare these stored readings with real-time data to determine if anything was amiss.

If an anomalous situation is detected, the only function of the control system is to stop the vehicle, using the normal braking rate if possible and emergency braking if necessary. Each vehicle would have an exterior, forward-looking video camera that could transmit to central control. This would allow the central operator to assess the situation, and drive the vehicle remotely if necessary. It may also be desirable to equip vehicles with an external loudspeaker and microphone to communicate with trespassers and warn them to leave the roadway.