Snow is synonymous with Canada, but this morning’s snow and the Canada Line did not mix. So why is snow and ice such a frustration with rapid transit lines?

The third rail is near the top with the yellow cover.

First of all, snow and ice can affect how the trains get their power. The Canada Line runs off a single third rail using a shoe that glides across the top. During inclement weather, snow and ice can build up causing trains to lose electricity and thus stop moving. The Expo and Millennium lines are not susceptible to this type of interference because the power rails are mounted horizontally over each other. The trains that operate on these two lines use collection shoes that collect electricity from the sides of the power rails, rather than the top.

There are multiple ways to mitigate the problem. Other systems, such as the Chicago ‘L’, use sleet scrapers which brush snow and other obstacles off the third rail ahead of the collection shoe. A deicing solution can also be  sprayed onto the third rail to prevent ice from forming and interfering with the electrical pickup. Alternatively, frequent use helps to lower the risk of build up. TransLink already does this by running “ghost trains” which are effectively empty trains around the system to assist in reducing the build up of snow.

Another common issue is that snow and ice accumulate between switch points which is critical at major junctions or turn-arounds. The Expo and Millennium Lines utilize a seamless type of switch, called a swingnose, that closes all openings to allow a smoother trip. The switch points must move all at once — snow and ice can get caught in the gaps and prevent the switch points from making full contact with the rails. This can be disastrous if a train crosses over where the points have not fully closed.

Frequent use should help keep the switch clear, but a switch heater may be employed to keep the rails warm so that snow or ice doesn’t build up. As a last resort, human intervention may be required.

There’s no perfect solution to prevent snow (or any type of weather) from making the trip troublesome. TransLink has posted a press release on their winter contingency plans for 2010. Besides, it could always be worse.