Other Considerations
With increasing diesel fuel costs and problems caused by particulate matter and NOx emissions in cities, trolleybuses can be an attractive alternative, either as the primary transit mode or as a supplement to rapid transit and commuter rail networks.
It has been suggested that trolleybuses will become obsolete in a future hydrogen economy, but direct electric transmission is at least twice as efficient as the alternative, viz. conversion of energy into hydrogen, transportation and storage of the hydrogen and its conversion back into electricity by fuel cells.
Being electric, trolleybuses are very much quieter than diesel- or petrol-engined vehicles. While this is mainly seen as a benefit, it does also make it easier for unobservant pedestrians and other motorists to miss hearing a trolleybus when crossing a street and risk being struck. A speaker attached to the front of the vehicle can raise the noise to a desired "safe" level. This noise can be directed to pedestrians in front of the vehicle, as opposed to motor noise which typically comes from the rear of a bus and is more noticeable to bystanders than to pedestrians.
Trolleybuses can share overhead wires and other electrical infrastructure (such as substations) with tramways. This can result in cost savings when trolleybuses are added to a transport system that already has trams, though this refers only to potential savings over the cost of installing and operating trolleybuses alone.
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