covers 23 km in 2 charges. Sinautec estimates that one of its buses has one-tenth the energy cost of a diesel bus and can achieve lifetime fuel savings of $200,000. Also, the buses use 40 percent less electricity compared to an electric trolley bus, mainly because they are lighter and have the regenerative braking benefits. The ultracapacitors are made of activated carbon, and have an energy density of six watt-hours per kilogram (for comparison, a high-performance lithium-ion battery can achieve 200 watt-hours per kilogram), but the ultracapacitor bus is also cheaper than lithium-ion battery buses, about 40 percent less expensive, with a far superior reliability rating. There is also a plug-in hybrid version, which also uses ultracaps. Future developments Sinautec is in discussions with MIT's Schindall about developing ultracapacitors of higher energy density using vertically aligned carbon nanotube structures that give the devices more surface area for holding a charge. So far, they are able to get twice the energy density of an existing ultracapacitor, but they are trying to get about five times. This would create an ultracapacitor with one-quarter of the energy density of a lithium-ion battery. Future developments includes the use of inductive charging under the street, to avoid overhead wiring. A pad under each bus stop and at each stop light along the way would be used. Drawbacks As with other electric vehicles, climate control and extremely cold weather will weaken the performance of electric buses. In addition, terrain may pose a challenge to the adoption of electric vehicles that carry stored energy compared to trolleybuses, which draw power from overhead lines. Also, compared to trolleybuses, battery electric buses have lower passenger capacity because the weight of the batteries increases axle loads in jurisdictions where there are legal axle load limits on roads. Even when conditions are favorable, internal combustion engine buses are frequently diesel powered, and diesel is relatively inexpensive per mile. High local utility rates (especially during periods of peak demand) and proprietary charging systems pose barriers to adoption. Makers and models School use North America In 2014, the first production-model all-electric school bus was delivered to the Kings Canyon Unified School District in California's San Joaquin Valley. The Class-A school bus was built by Trans Tech Bus, using an electric powertrain control system developed by Motiv Power Systems, of Foster City, California. The bus was one of four the district ordered. The first