Trams can carry between 220 and 500 passengers. By contrast, a bi-articulated trolleybus can carry just 160 passengers. This means that trams are more economic to run than trolleybuses.
Trams can adapt to demand by adding more carriages during rush hour (and removing them during off-peak hours). This isn’t possible with trolleybuses.
Trams can be reversed, but trolleybuses require a wide turning circle.
Because they’re on rails, trams can turn tighter corners than trolleybuses.
Trams provide a smooth ride. But with trolleybuses, the ride depends on the road surface.
Trams provide a ride with none of the vertical oscillations associated with trolleybuses.
A tram requires just one overhead cable because the metal rail acts as an earth. But because trolleybuses have rubber tyres, they require two overhead cables. This doubling up of the amount of overhead cable significantly increases visual pollution.
Tram pantographs don’t become detached from the overhead cables, whereas trolleybus pantographs frequently do.
To prevent their pantographs becoming detached, trolleybuses cannot stray too far from their overhead cables. This means that they keep following the same “track” on the road, and thus cause damage to the road surface. And where there is level boarding at bus stops, they create deep ruts in the tarmac.
Tramways are narrower than trolleybus lanes. This saves valuable space on narrow streets.
Trams can share railway lines with trains.
Tram systems typically attract between 30 and 40% of their patronage from former car trips. With bus-based systems, the figure is less than 5%.
You can hear a tram coming, but because of their rubber tyres and electric motor, you can’t hear a trolleybus coming. This is why in the UK trolleybuses used to be known as “Silent Death” and “Granny Killers,” and why in Australia they were known as “Whispering Death.”