Why The Montreal Metro Has Rubber Tires

Montreal loves to trumpet its difference from other cities in North America. But why does that difference have to extend to the very components of our metro system?

A look back at discussions around the planning of the metro system in the 1960s offers at least some insight into the seemingly peculiar use of rubber tires on the Montreal metro.

What are the service benefits of a rubber tire metro?

Speed.

In 1961, Montreal metro planners published a study comparing possible tunnel configurations, train sizes and technology, including an assessment of the advantages and disadvantages of rubber tires. Many of their benefits derive from the frictional grip of tires on their tracks.

The study authors showed, for example, that rubber tire trains could accelerate at a faster rate than many subway trains that used steel wheels on steel rails.

According to one diagram, Parisian rubber-tire (pneumatic) metro trains were able to reach a speed of 25 miles per hour (mph) in 8.62 seconds, faster than trains in eight other global cities.

Though steel-wheel trains in Milan, Toronto and Chicago were able to accelerate faster than their counterparts in Paris, study authors said it was "theoretically" possible for rubber-tire trains to speed up even more quickly. (Though passengers, authors suspected, would find such quick acceleration "intolerable.")

The pneumatic trains of the French capital were also able to stop more quickly both in their approach to stations (25 to 0 mph in 7.8 seconds) and in emergency situations (4.5 seconds) than subway trains in most 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're needy and expensive.

Rubber tire trains had higher energy consumption and maintenance costs, the study authors found.

That friction between tires and track meant trains needed more power to get going. This was another reason why the authors concluded maximum acceleration on rubber tire trains would be unfeasible: "the costs of such acceleration rates in terms of electrical energy consumption would make such an operation unacceptable."

They outlined two reasons for greater maintenance costs on systems with rubber tires. First, they said, pneumatic trains simply require more parts, and more parts meant more to keep up. And second, tires wear out.

While for every million dollars of maintenance steel wheel train cars in Toronto were able to travel 5,587,000 miles, Parisian rubber tire trains could only go 2,688,000 miles.

How do rubber tires affect construction?

What seemed to be pneumatic trains' greatest advantage was their greater ability to climb. They could mount inclines as much as twice as steep as steel-on-steel trains. That also meant lesser construction costs.

The slope-climbing ability of rubber tires allowed metro construction using trenches rather than tunnelling through rock.

In one projection included in the study, construction for a hypothetical 14.7-mile metro in Montreal would have cost almost 10% less with a small-gauge (meaning the tracks are closer together) rubber-tire system than a larger gauge system.

Was there a political argument for rubber tires?

At least according to one French official.

In a 1961 report, a commercial advisor for 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 economic and cultural ties with France and distinguishing 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 that country, which, however beneficial it may often be materially, seriously compromises the independence of Canada and the survival of its French part."

"The vast enterprise that constitutes the construction of a metro," the French official said, would also foster "many technical, industrial and financial contacts between specialists of the same language who know each other too little at the present time."