In engineering terms, the Trolleybus is clearly the most efficient 'green' public service vehicle available.

The latest control technology for Trolleybuses use alternating current [AC] motors, controlled by inverters that create variable voltage and frequency AC for the motors, from the DC overhead line supply. The supply voltage is between 600v and lately, 750v.

AC motors and control systems have many advantages over traditional DC systems, including greater reliability, less maintenance, greater efficiency, sophisticated control over acceleration and jerk rates. The efficiency advantages should be substantial - up to one third less power consumption than DC systems. Maintenance and reliability advantages should also be substantial - at least ten times more reliable than previous generation installations.

Recent developments have permitted driving axle designs with an AC motor per wheel, or within the wheel, eliminating differentials and half shafts, permitting further simplification and greater flexibility in overall layout and facilitating low floors. Such designs, eg. the Neoplan N6121 and Irisbus Cristalis are just entering service.

Much of the engineering of Trolleybuses is, however, similar to diesel buses. Modern European Trolleybus designs e.g. the Van Hool A300 series are usually derived from proven diesel bus designs. Trolleybus electrical equipment is very flexible, consisting mainly of modules connected by flexible cables that need no special consideration for accessibility, cooling, or noise and vibration. Trolleybuses, therefore, present easier design challenges compared to diesel systems.

The energy generated by electric braking is either dissipated in resistors on the vehicle, or fed back into the overhead line, a system known as regenerative braking. Depending on the type of route and pattern of service, energy savings from regenerative braking can be substantial - up to one third less energy consumption.

Many Trolleybuses operate without any source of power other than the overhead wires. In modern traffic situations, some ability to operate from the overhead wires may be considered essential. Modern battery systems or auxiliary small [diesel] generator systems permit operation at 10 to 20 mph, for considerable distances, independently of overhead wires. Some new developments in battery technology, such as sodium chloride/nickel, might provide an off wire service abilty in sensitive 'heritage' areas. Specially designed flywheel units might provide acceleration 'buffers' that could reduce the overhead installation sizing.

While buses and Trolleybuses are normally manually steered, there are advantages in automatic guidance systems over parts of routes. Automatic guidance is valuable on private alignment [busways] as it reduces the width needed for the right of way. Automatic guidance is also very useful for automatic docking at raised platforms [level entry stops] Automatic guidance on current British busways is mechanical in nature and basically not compatible with other traffic. There are at least two systems of automatic guidance available, electronic in nature, that are compatible with other traffic. One follows a white line on the road surface, the other is a buried cable as used in the access tunnel for the main Channel tunnels.

There is no environmentally friendlier way of operating urban bus routes than with Trolleybuses.