[rob74]

However this study is about the impact of the noise on passengers, not people living beside the tracks. For passengers, I think a tunnel (which reflects the noise back) is worse than an above-ground track. Of course, for both avoiding tight curves during planning and good track maintenance help a lot...

The article you linked also mentions some of the disadvantages of rubber-tire metros:

> Rubber tires wear faster and must be replaced more frequently, meaning more waste. Trains on the Paris Metro – which pioneered the use of rubber tires and inspired Montreal’s design -- can run for 4,325,917 km for every $1 million in maintenance; Toronto’s steel wheeled trains can go for 8,991,405 km-- more than double. Montreal’s Metro requires approximately 2900 new tires every year – that’s a lot of old tires being discarded. When these tires break down, they also create airborne particulate matter that can remain in the environment for years, contributing to air pollution.

The friction between rubber and concrete is greater than between a steel wheel and steel tracks. This means that more energy is required to push Montreal’s cars forward than Toronto’s