Editing Personal rapid transit (section)

====Energy efficiency====
The [[energy efficiency in transport|energy efficiency]] advantages claimed by PRT proponents include two basic operational characteristics of PRT: an increased average load factor; and the elimination of intermediate starting and stopping.<ref>{{cite web|url=http://citeseer.ist.psu.edu/594390.html|title=CiteSeerX}}</ref>

Average load factor, in transit systems, is the ratio of the total number of riders to the total theoretical capacity. A transit vehicle running at full capacity has a 100% load factor, while an empty vehicle has 0% load factor. If a transit vehicle spends half the time running at 100% and half the time running at 0%, the ''average'' load factor is 50%. Higher average load factor corresponds to lower energy consumption per passenger, so designers attempt to maximize this metric.

Scheduled mass transit (i.e. buses or trains) trades off service frequency and load factor. Buses and trains must run on a predefined schedule, even during off-peak times when demand is low and vehicles are nearly empty. So to increase load factor, transportation planners try to predict times of low demand, and run reduced schedules or smaller vehicles at these times. This increases passengers' wait times. In many cities, trains and buses do not run at all at night or on weekends.

PRT vehicles, in contrast, would only move in response to demand, which places a theoretical lower bound on their average load factor. This allows 24-hour service without many of the costs of scheduled mass transit.<ref>{{citation
 | author = Anderson, J. E.
 | year = 1984
 | title = Optimization of Transit-System Characteristics
 | publisher = Journal of Advanced Transportation, 18:1:1984, pp. 77–111
}}</ref> <!--This article may be viewed using Google's cache at:
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ULTra PRT estimates its system will consume 839 BTU per passenger mile (0.55 [[megajoule|MJ]] per passenger km).<ref name="Lowson">{{cite web
 | last = Lowson
 | first = Martin
 | url = http://www.advancedtransit.org/wp-content/uploads/2011/08/A-New-Approach-to-Sustainable-Transport-Systems-M.-Lowson.pdf
 | title = A New Approach to Sustainable Transport Systems
 | year = 2004
 | access-date = August 30, 2017
}}</ref><ref>The conversion is: 0.55 MJ = 521.6 BTU; 1.609 km = 1 mi; therefore, 521.6 x 1.609 = 839</ref> <!-- #####I'm removing the below SkyTran section for now, because the reference link seems to be bad - I only get a page full of dead links. If that page is restored, we can restore this section. -ATren, April 2008.#####
SkyTran, a PRT concept using significantly smaller vehicles than other designs, may require only 11 horsepower (9 KW) to cruise at 160 km/h (100 mph), which translates to 151 BTU/passenger mile or 0.1 MJ per passenger km.  However, SkyTran's predicted energy usage is unconfirmed in real world practice, since no SkyTran system or prototype has yet been built. Also, Skytran's small vehicle does not permit disabled passengers, which would require accommodation using other, less energy-efficient modes.<ref name="Malewicki">{{cite web
 | last = Malewicki
 | first = Douglas
 | url = http://www.skytran.net/18EnergyEff/02Energy.htm
 | title = (doc) SkyTran's Super Energy Efficiency
}} Note that this page presents a comparison of seating arrangements; the actual numbers shown for the planned 2-passenger tandem seating arrangement are 10.65 horsepower and 8.85 kilowatts.  The English unit calculation is 8.85 kW / 2 passengers * 3412 (BTU/hour)/kW / 100 mile/hour = 151.0 BTU/passenger mile.  The metric calculation is 8.85 kW / 2 passengers * 3.6 (MJ/hour)/kW / 160 km/hour = 0.0996 MJoule/passenger km.
</ref>--> By comparison, cars consume 3,496 BTU, and personal trucks consume 4,329 BTU per passenger mile.<ref name="edbk">{{cite web
 | publisher = U.S. Dept. of Energy
 | url = http://cta.ornl.gov/data/chapter2.shtml
 | title = Transportation Energy Databook, 26th Edition, Ch. 2, Table 2-12
 | year = 2004
}}</ref>

Due to PRT's efficiency, some proponents say solar becomes a viable power source.<ref>{{cite web
 | year = 2003
 | url = http://www.solarevolution.com/solutions/presentations/ATRA20061118.xls
 | title = ATRA2006118: Solar PRT, p.89
 | publisher = Solar Evolution
 | format = Xcel Spreadsheet
 | access-date = 18 November 2006
 | archive-date = 30 March 2007
 | archive-url = https://web.archive.org/web/20070330035545/http://www.solarevolution.com/solutions/presentations/ATRA20061118.xls
 | url-status = dead
 }}</ref> PRT elevated structures provide a ready platform for solar collectors, therefore some proposed designs include solar power as a characteristic of their networks.

For bus and rail transit, the energy per passenger-mile depends on the ridership and the frequency of service. Therefore, the energy per passenger-mile can vary significantly from peak to non-peak times. In the US, buses consume an average of 4,318 BTU/passenger-mile, transit rail 2,750 BTU/passenger-mile, and commuter rail 2,569 BTU/passenger-mile.<ref name="edbk"/>