What are the service advantages of a metro on tires?
A 1961 study comparing possible tunnel and train sizes for the subway explored the many advantages and disadvantages of rubber tires. Many of these benefits come from the frictional grip of the tires on their tracks.
The study authors showed, for example, that trains on rubber tires could accelerate faster than many subway trains that used steel wheels on steel rails.
According to one diagram, rubber-tyred (pneumatic) Paris metro trains were able to reach a speed of 25 miles per hour (mph) in 8.62 seconds, faster than trains in eight other cities around the world.
Although the steel-wheeled trains in Milan, Toronto and Chicago were able to accelerate faster than their Parisian counterparts, the study authors said it was “theoretically” possible that the rubber-tyred trains accelerated even more. quickly. Passengers, the authors suspected, however, would find such rapid acceleration “intolerable”.
Pneumatic trains in the French capital were also able to stop faster both when approaching stations (25 to 0 mph in 7.8 seconds) and in emergency situations (4.5 seconds) than metro trains of most of the other cities included in the study.
It took trains in Toronto, by contrast, 10 seconds to stop from a speed of 25 mph in normal service and 6.9 seconds with emergency brakes.
What are the disadvantages ?
They are needy and expensive.
Rubber-tyred trains had higher energy consumption and maintenance costs, the study authors found.
This friction between the tires and the track meant that the trains needed more power to start. This is another reason why the authors decided that it would be impossible to achieve maximum acceleration on rubber-tyred trains: “The costs of such acceleration rates in terms of electrical power consumption would make a such an unacceptable operation”.
The authors pointed to two reasons for the higher maintenance costs on rubber-tyred systems. First, they said, pneumatic trains simply require more parts, and more parts mean more to keep up. And second, the tires wear out.
Whereas for every million dollars in maintenance, the steel-wheeled train carriages in Toronto could travel 5,587,000 miles, the rubber-tyred trains in Paris could only travel 2,688,000 miles.
How do rubber tires affect construction?
What seemed to be the biggest advantage of pneumatic trains was their greater ability to climb. They could climb grades up to twice as steep as steel-on-steel trains. It also meant lower construction costs.
The slope-climbing ability of rubber tires allowed more subways to be built using trenches rather than digging tunnels in rock.
In a projection included in the study, building a hypothetical 14.7-mile subway in Montreal would have cost almost 10% less with a narrow-gauge rubber tire system (meaning the tracks are more close together) than a system with wider spacing.
Was there a political argument for rubber tires?
At least according to a French official.
In a 1961 reporta trade adviser at the French Embassy in Canada suggested that the use of French engineering techniques and metro technology, such as rubber tires, served Montreal Mayor Jean Drapeau’s goal of strengthening ties economic and cultural relations with France and to distinguish Quebec from the rest of North America.
Privately, the official said, the mayor expressed a “desire not to turn to the United States, because the province of Quebec is trying to free itself from the economic empire of this country which, however beneficial it often materially, seriously compromises the independence of Canada and the survival of its French part.
“The vast undertaking that is the construction of a metro”, declared the French official, would also promote “numerous technical, industrial and financial contacts between specialists of the same language who know each other too little at the present time”.