Automated Microbus: Vehicle Design
The Automated Microbus is a proposed 6-passenger Automated Road Vehicle with a top speed is 20-25 mph (32-40 km/hr), depending on the application. The Microbus cannot be considered in isolation, but is part of a complete system that also includes an exclusive two-way roadway, intersections, stations, and an operating policy with a quick response failure management strategy.
The Microbus passenger compartment, from front to back, consists of a two-abreast, rear facing bench seat, an open floor area about 68" (1.7 m) long by 51" (1.3 m) wide, and a forward facing, two abreast bench seat. Two sideways-facing "jump" seats are on one side of the open area, and are normally folded up. The front and rear bench seats are far enough apart to allow two strangers to share the vehicle without feeling crowded. The seats are arranged so everyone can see everyone else, which will increase the passenger comfort level when the vehicle is shared. A low roofline, needed for stability in a narrow vehicle, precludes adult standees. All passengers board from platforms about 12" (0.3 m) high, level with the vehicle floor.
The vehicle is intended to be fully compliant with the Americans with Disabilities Act (ADA). Despite the Microbus' name, it's believed that operation on an exclusive roadway calls for people mover, rather than bus, standards. APM Standards, Part 2, Section 188.8.131.52 states that people movers with passenger compartments less than 22 ft (6.7 m) long should provide a space of 30 by 48 inches (76 by 122 cm) for one wheelchair. The total length of the Microbus is 12.5 ft (3.8 m), and its open floor area provides the required space for a wheelchair facing either sideways or longitudinally, with room for at least two other riders.
As far as interior dimensions for maneuvering a wheelchair are concerned, a close analog to the Microbus passenger compartment is an elevator car. An elevator that's 68 by 54 inches (173 by 137 cm) with a 3 ft (0.9 m) door at one end of the long side is ADA compliant (see diagram (b) here). The Microbus is slightly narrower, but it's believed that its wide door opening more than compensates.
Center parting power doors on one side of the vehicle provide an unobstructed opening 5 feet (1.5m) wide. In addition, a hinged roof panel pops up to allow passengers to walk part way on board (the interior height is 5 ft). This door arrangement can be seen in an unusual concept van called the Mobile Terrace that was introduced by Suzuki at the 2003 Tokyo Motor Show. However, the proposed Automated Microbus is very different from the Mobile Terrace in that the Microbus has doors on only one side, as well as a lower floor and a different seating arrangement. The Microbus doors are on the side of the vehicle that faces the inside of the two-way roadway, the opposite of an ordinary bus. This is to allow easy evacuation of passengers to a vehicle in the adjacent lane in case of a breakdown.
The chassis of the Microbus could be purchased off-the-shelf. A number of Neighbor Electric Vehicles and extended length golf cars are suitable, including the new 6-passenger GEM NEV and the 6-passenger Club Car Villager. Some upgrades might be necessary to increase top speed and/or payload.
A number of alternative power sources are possible. Three possibilities are batteries, fuel cells, and compressed natural gas. Battery packs could be exchanged several times a day, to make vehicles continuously available. Fuel cells, like batteries, would provide zero emissions, and their lower weight should translate into at least a small benefit in terms of reduced construction and maintenance costs for the exclusive roadway. Currently, fuel cells are very expensive, and are not yet practical as a power source for automobiles. However fuel cell costs are roughly proportional to the peak power requirement. The Microbus would require much less power than an auto, perhaps one tenth as much (8 kW vs. 80 kW), because of its lower top speed and the fact that acceleration will be held to low levels suitable for standees. (Acceleration is limited because it's difficult to guarantee that children and short adults are seated, and wheelchairs would be unsecured as in large people movers.) A small battery or ultracapacitor could supplement the fuel cell during occasional hill climbing.
Compressed natural gas (CNG) would be an excellent power source if low, rather than zero, emissions are acceptable. Small, internal combustion engines that run on CNG are readily available, and in fact can be purchased as a factory option on certain parking patrol vehicles.
Finally, a lightweight fiberglass body would provide complete enclosure. Most applications would require air conditioning, but even batteries should be able to provide enough power for an efficient cooling system.