Trams use electricity for propulsion which means that there are no emission of any harmful exhaust in the city environment. Public transport on rails also attracts drivers to a larger extent than other public transport, which means that the total amount of carbondioxide emissions is reduced.

The electricity used for the trams can be produced in many different ways. The best is to use renewable resources. But even if the electricity is generated through the burning of coal or oil, it's better that the electricity is produced at a single location where the process is more efficient, compared to for instance diesel buses each equipped with their own engine. The fact that electricity is transmitted to the trams via overhead catenary or in ground power supply, means that the trams don't have to carry their own energy with them in tanks or batteries, which means additional space can be offered to the passengers. For catenary free operations there are of course options for batteries too. 
 

Trams are energy efficient

Electric propulsion is very energy efficient, due to the thermal efficiency in electrical motors. Public transport on rail, using steel wheels on steel tracks has a low rolling resistance compared to vehicles on rubber wheels. The estimated energy use for a diesel bus is 0,080 kWh per place kilometer, while a tram only uses 0,017 kWh per place kilometer. Battery buses are better than diesel buses, but do not come near the efficiency of a tram.

When braking, modern trams can also feed electricity back in the grid, that other trams can use. Depending on how the system is designed, this electricity can also go out into the general grid. Lately, there has also been developments in other technologies such as super capacitors and flywheels, which can store electricity temporarily. This means that the energy consumptions on trams can be brought down with about 25%. Feeding electricity back in the system is especially useful in city traffic, where starting and stopping are frequent. Super capacitors can also placed on the tram, allowing for catenary free operations over a limited distance. For longer catenary free operations, batteries (and sometime diesel engines) are used instead. 

Modern trams are quiet

Under normal circumstances trams are quiet. A method commonly used to reduce noise further is to build tracks in grass, which lowers the noise with about 5 dB(A). As a bonus, the city also gets greener and have an easier way to cope with sudden heavy precipitation. Noise and vibrations, for example in curves, can be a problem but there are ways to mitigate this both during the construction of the tramway and in a later stage. The trams can also be modified to run quieter if specific problems are noted.