Drawbacks of Trolleybuses

Because of the much higher cost of trolleybuses, and their need for costly overhead lines and electrical substations, trolleybuses are a more expensive option than diesel buses.

Diversions are not normally possible outside of city centres (where trolleybuses can be diverted along adjacent streets with overhead lines).

It’s impossible without additional overhead lines for trolleybuses to take short-cuts during less busy periods, or when running empty back to the depot, something which is possible with diesel buses. This is why trolleybus services are sometimes replaced overnight by diesel bus services. Passengers can find this confusing.

School and works trolleybus services are not possible if the school or factory isn’t located on the trolleybus route. Similarly, they cannot be used for class outings if the destination isn’t on the trolleybus route.

Diesel buses need to be kept in reserve to run an emergency service in the event of power failure, construction or road works blocking the route, maintenance work on the overhead lines, icing of the overhead lines, storm damage to the overhead lines, and accidents. If insufficient diesel buses are held in reserve, they have to be rented from other operators. If this is not possible, the service on the trolleybus route has to be restricted.

Trolleybuses cannot overtake one another unless an additional set of overhead lines is provided along with a switch, or unless the vehicles have off-wire capability. Because trolleybuses cannot normally overtake one another, it’s not usually possible to run an express trolleybus service.

Trolleybuses are unable to turn to avoid hazards, whereas a diesel bus can turn at any major junction. Furthermore, it’s not usually possible to supplement trolleybus services by adding additional vehicles in order to cope with extra demand, as the sub-station capacity can usually only cope with the demands of regular operation.

Should a transport operator desire fully flexible use of employees, then the entire pool of drivers must be trained to drive trolleybuses despite the additional cost.

Not every trolleybus line can be extended. Level crossings with electrified railway lines or low underpasses both prevent trolleybus lines being extended.

To prevent dewirements, trolleybuses have to slow down at turns and as they pass switches in the overhead lines. Trolleybuses which don’t have battery back-up are left stranded by dewirements. Dewirements can block a whole junction.

It’s not possible to have trolleybus systems with several branch routes connecting the suburbs to central lines owing to the cost of the additional infrastructure that would be required. Instead, passengers wishing to travel to the suburbs are required to change to diesel buses at the edge of the central zone. Broken journeys such as these make trolleybuses unattractive to many.

It’s often claimed that trolleybuses are more environmentally friendly than diesel buses. But this is only true where the electricity is derived from renewable sources such as hydro-electic. Where the majority of the electricity is derived from burning hydrocarbons, as is the case in most European countries, the diesel bus has a smaller carbon footprint.

Trolleybuses require twice the amount of overhead cable as trams, and this results in complex arrangements of cable at junctions. The proliferation of cable can create a webbed look which can seem to obscure the sky and spoil the view of historic or architecturally impressive buildings.

In narrow streets, the overhead lines required by trolleybuses can prevent the use of turntable ladders required by fire services to extinguish fires.

A trolleybus has a higher unladen weight than a diesel bus. This affects the number of passengers it can carry. A trolleybus with the same chassis as a diesel bus has a smaller passenger capacity.

Trolleybuses require high voltages and currents which increases the risk of fire. Lightning strikes cause voltage surges and these too increase the risk of fire. Lightning strikes can also damage cable junctions and trolleybuses close to the area of high electrical charge.

In winter, icing of the overhead lines can lead to higher resistance of the overhead lines and arcing. Old-fashioned trolleybuses with simple controls can sometimes continue to operate. But modern trolleybuses with sensitive electronic controls experience great difficulties due to arcing. Furthermore, the weight of ice can cause overhead lines to break. Special vehicles are required to scrape the ice from the overhead lines and spray them with anti-freeze. Sometimes the trolleybuses themselves are fitted with pantographs which can spray anti-freeze.

Snow chains cannot normally be used on trolleybuses as they can cause short circuits between the overhead lines and snow on the road or metal grates and other metallic elements bedded in the road surface. Instead, trolleybuses can be fitted with gritters which increase grip on slippy surfaces. Gritters are not as effective as snow chains.