Editor:
Re: Look at the big transit picture, Murphy's Law, July 15
Ted Murphy is correct. We should consider the big picture.
There is a range of public transit technologies to choose from. They vary greatly in cost and capacity. At the lowest cost and capacity are busses, then rail transit systems, including light rail (street cars), intermediate capacity (SkyTrain), and the most expensive, heavy rail (subways). A separate category is commuter rail that refers to railroad passenger trains.
Rail transit systems vary in peak hour capacity, depending on technology selected, from perhaps 5,000 to 40,000 passengers per hour per direction. The design capacity is a function of system speed, headway, train length, and passenger density per unit of length.
SkyTrain's design capacity is 15,000. It achieves this with 90-second headways, 20-second station dwell times, and trains of either four or six cars depending on car length. Short headways are achieved by driverless (computer controlled) operation and segregated guideways, either at grade, elevated or below grade.
It is my impression that over the 25 years since it opened SkyTrain has proven an excellent choice for the communities it was selected to serve.
Other Lower Mainland communities, however, do not require a system of such capacity, and may be more economically served with lower cost technology.
One often reads that light rail can provide the same capacity as SkyTrain. This may be possible on segregated guideways that avoid all interference with automotive traffic, in which case the cost approximates that of SkyTrain.
Light rail cost savings are realized when they operate in mixed automotive traffic, in which case peak capacity drops to perhaps 5,000.
As a general rule-ofthumb, an intermediate capacity system such as SkyTrain is cost effective serving communities of perhaps one million people. Serving relatively much smaller communities south of the Fraser River, especially considering the high cost of a river crossing, argues for a much more cost effective bus system.
Ed Ries
