Comparison of Automated Microbus to Personal Rapid Transit
Automated Microbus vehicles and guideway are similar to some types of PRT, but the service concept is different
Personal Rapid Transit (PRT) was first proposed in the 1960's, and has had enthusiastic supporters ever since. While there is some disagreement on the details, it's generally described as a system of 3 or 4 passenger driverless vehicles running on exclusive guideways, which would be mostly aerial. All stations are on sidings, and all trips are non-stop, origin-to-destination. Individuals or groups traveling together get their own vehicle; there would never be sharing by strangers (however, there have been some suggestions that PRT vehicles be shared during peak periods).
No PRT systems are currently in service. There is a system called Personal Rapid Transit in Morgantown, West Virginia, but it uses larger, 21-passenger vehicles. Various PRT systems have been developed over the years, and the three closest to deployment readiness are ULTra, Vectus and the 2getthere CyberCab. An ULTra system is being deployed at Heathrow airport, London, and the 2getthere system is being installed in Masdar, Abu Dhabi.
The Vectus PRT system uses a custom guideway that provides lateral control mechanically. ULTra and the 2getthere vehicle are like the proposed Automated Microbus in that they use an ordinary electric vehicle chassis, which is guided along a flat surface by precise steering. This eliminates the need to develop custom mechanical components, and results in extremely low infrastructure costs for those sections that can be run at grade.
The following table compares the Automated Microbus with PRT systems in general.
|Characteristic||Automated Microbus||Personal Rapid Transit|
|Minimum Headway||5 seconds||0.5 - 3 seconds|
|Private vs. Shared Operation||Shared by strangers, although guaranteeing private vehicles (perhaps for a surcharge) during periods of low demand is possible||Private, although it has been suggested that PRT vehicles be shared by strangers during peak periods|
|Vehicle capacity||6 seated, typically no standees because of 5 ft (1.5 m) interior height. However there is nothing to stop individuals shorter than 5 ft from standing.||3 or 4 seated, depending on system. No standees.|
|Acceleration & Jerk Limits||Suitable for standees. A wheelchair would not be secured, which is also the case for large people movers.||Based on all passengers being seated|
|Typical system configuration||Hub and spoke||Grid|
|One way vs. two way roadway/guideway||Two way almost everywhere||Mostly one way|
|Transfers||Riders would sometimes need to transfer, usually at a hub station of a hub-and-spoke network. Most transfers would involve little walking and a wait of less than one minute. By requiring riders to transfer, the number of destinations for any particular origin station can be held to a maximum of about six. This allows much higher average vehicle occupancies.||None|
|Expected average occupancy, peak period, peak direction||5 passengers||1.2 passengers. This is based on observed peak period occupancy of cars on freeways; it might be greater if fares are high enough to cause passengers to "car pool".|
|Intermediate stops, other than transfers||Usually none||None|
|Response to vehicle failure||Transfer passengers to vehicle in adjacent lane. Then tow failed vehicle with any standard vehicle.||Depends on system.|
|At grade vs. aerial||Mostly at grade with short bridges or tunnels as necessary.||Either entirely aerial or a mix of aerial and at grade, depending on system.|
|Expected locations for systems||Mostly airports and suburbs. At particular locations where right of way happens to be available.||Airports, CBDs, eventually entire urban areas|
|Typical location for roadway/guideway||At grade along freeway or rail line (either operational or abandoned). In some cases routes could be run at grade on land taken from the edges of large parking lots or other open areas, with short tunnels under cross streets.||Aerial structure along arterial.|
|Typical station location||At grade at end of a short (perhaps 500 ft (150 m)) two-way, at-grade spur line. This allows the main roadway to be out of the way, while placing the stations in more convenient locations. For an example, see the possible North Bethesda system.||Aerial, on one-lane siding running parallel to aerial one-way line.|
|Relationship to conventional transit||Complementary -- solves "last mile" problem, although in some cases stand-alone Microbus systems could serve low-moderate demand.||Except for airport applications, PRT is usually presented as an alternative to a conventional system.|