I often wonder, how does it know?
Street Scene will appear each week showcasing the illustrations of local artist Jerry Waese.
STREET SCENE: How does it know which track to follow?
By Jerry Waese
Read more articles by Jerry Waese
4 comments
Yes, I know this is supposed to be an artistic statement, an existential question about paths not taken, but for those of a more prosaic bent …
There are two types of track switch, manual and automatic. Of the latter, there are two flavours, working and not working, about which more later.
Manual switches are found (in theory) at locations not used very often, or where the TTC is too cheap to install one to assist in frequent short turn movements or diversions. These switches are set by hand by the operator using a switch iron, and they must be manually reset for the following car.
Automatic switches are found (generally) at locations where cars change route commonly, as well as at many of the left turns on the system where it is (a) more dangerous if the switch is left open and (b) more difficult for an operator to walk back through the intersection to reset it manually.
Before the longer cars (the ALRVs) were introduced, automatic switches were controlled through a contactor on the overhead wire and a separate contact on the trolley pole of the streetcar. This only works if all cars are the same length. After the ALRVs, the system was changed to use loop antennae in the pavement.
When a car approaches a switch, the antenna picks up a signal controlled by the operator telling the switch which way to turn. If everything works, the switch is locked in the desired direction and, where there are special traffic signal phases to assist the turn, these are added to the next cycle. The switch is unlocked when another transmitter at the back of the car passes over the antenna giving the “all clear”. When cars run in trains, only the transmitters at the front of the first car and back of the last car are active so that switches remain locked while the entire train passes over them.
This antenna system never worked very well, and the TTC has a project on the books to replace it, but I don’t know when that’s going to actually start. Meanwhile, because some switches are unreliable, all facing point switches operate on something close to a “stop and proceed” order resulting in slow, jerky operation through intersections.
In your choice of paths through life, I am not sure whether you have to deal with such complex, unpredictable technology.
2009?
steve munro: i genuinely hope that you never stop caring about streetcars and writing about them on the web — nice post!
super info!
re tech chaos
yes it’s everywhere
interfaces galore
like biblical babel towers