The monorail itself uses no carbon-based fuels and so does not pollute, unlike cars and buses. The electricity used to power the locomotive may come from an gas or coal-fired power station which does produce pollution, but as the use of alternative energy increases this problem will be reduced.
As monorails run around elevated tracks there is no risk of cars getting stuck on crossings. There is a reduced risk to pedestrians for the same reason. The monorail itself is also safer as there is no risk of the carriage derailing. This leads to fewer accidents and delays, meaning the system is a lot more efficient than a ground-based rail system or buses.
As there are fewer accidents and no friction between rails and wheels, the system requires less maintenance than a road or train track. This means fewer delays and less expensive maintenance.
Although monorails need less regular maintenance, they can be more expensive to build initially. This is because the system requires the elevated track and supports, which are more costly than a basic railroad. This is assuming that increased infrastructure is not required to build the railway, such as tunnels. There is also an advantage for monorails in that construction time is a lot less, as the construction process itself is relatively simple. This means fewer delays and less disruption for local people and businesses during building.
Perhaps the greatest drawback for monorails is what happens when something does go wrong, either with the track or train. On a standard railway there are many lines a train can travel on; on a monorail it is limited to one. If a section of track needs to be replaced, the entire system needs to be shut down resulting in no service rather than reduced service.
Monorails look impressive, modern and clean. A transit system suspended above the city is not only good for transportation, but can also be a tourist attraction. Despite the Seattle monorail being built in 1962, they are still seen as futuristic. Monorails are also practically silent, as opposed to trains which make a noise traveling along rails.
