Tram control

[PGC]

I was recently pointed to this video on YouTube

 

 

and it got me wondering, how were (or possibly even, are) trams directed. Did or do they have signalmen as the railways did/do? If not, how did the trams get pointed in the right direction at junctions?

 

Thanks

 

Phil

[Edwin_m]

Tram signalling today is by systems similar to traffic lights, though they use white horizontal and vertical bars instead of coloured lights so as not to confuse other road users.  Not sure what system was used in the past but I would be surprised if the trams didn't just obey the normal rules of the road including traffic signals and police on point duty. 

 

Tramways have always used trailing or sprung points whenever possible.  In some cases staff were posted at junctions to operate facing points.  Another option is for the point to be electrically operated when the tram draws power, rather than coasting, when passing under a special insulated section of overhead line.  Rarely used points were and still are operated by the driver using a "point iron", a metal rod inserted in the flangeway or into a special slot and used as a lever. 

 

All light rail systems today have a transponder on each tram, which passes over loops laid between the rails anywhere the tram is likely to stop and at other places too.  When this happens the tram transmits information including its vehicle number, route code (programmed by the driver) and keystrokes the driver may operate.  These serve several purposes including allowing the control room to locate the tram and operating passenger information displays.  On the approach to a junction the system will recognise the route code, set the points appropriately and at most junction request priority at the traffic signals, though this is not always granted especially if another tram has already obtained priority.  Where there is a risk of people being stood on a point, it will not be operated until the tram is very close and sometimes won't operate automatically but the driver has to request it via a button in the cab when he can see there is nobody in danger. 

[BR60103]

In olden days, there were a couple of common ways of controlling tramway points.(In North America, anyways).

Manual worked with all of them, including the ones with electric gizmos.  Each car had a "switch iron" -- a large crowbar that was used to pry the switchblade over.

The common method of electric operation used some sort of motor/solenoid under the street. This was controlled by the trolley pole passing a contactor or something. If the car was drawing current as it passed, the switch went one way; coasting it went the other. In dense traffic the car might have to be operated with both brakes and motors on.

Toronto had a contact on the side of the trolley pole shoe or wheel that met a brass strip hanging beside the wire. There was a button on the dash that could power or not power the contact turning or straightening the switch. (Called Necessity Action -- the motorman had to take the necessary action).  There was another type called Self Restoring -- the point was turned manually but straightened automatically by the following car. If the following car also wanted to curve, the motorman had to get out and turn it.

 These switches were usually restricted to places where they were used frequently -- where routes diverged or cars were turned back.  It was rare for an intersection to have automatic switches going both ways.

 

Since the introduction of induction controls (Toronto now has 2 lengths of streetcars) the mechanisms have become extremely unreliable.

 

The point blades went over with snappy clunk.  If there was a puddle of water over it, it would shoot up in the air.

 

Let's see the "dummy overhead" boys 2-rail that layout.

[Londontram]

Have a look at this film from just before 1:50 and 6:15 (Actually the whole film is worth watching) the points man is reading the route numbers off the front of the trams and is directing them accordingly stood in the open in all weather in London most of the system stead manual operated until the end but some of the last built tram routes round Eltham in south east London had points operated by the overhead as described by the other members

 

[Gwiwer]

Trams were directed as discussed by various methods ranging from the crude to the hi-tech.  They still are.  Melbourne operates what is claimed to be the largest tram network in the World (some sources claim Russian systems  to be larger) with a fleet of over 500 trams dating from 1936 - 2013 delivery and with the majority dating from the 1970s - 1980s.

 

Across hundres of kilometres of route there are many junctionss including one of the few remaining "grand unions" which is a crossroads in the track with all four turns also available.  Try re-creating that in model form!

 

Many points are controlled by a simple induction-loop system with the driver selecting a direction (straight or turn) from the control panel and the command transmitted via a wire loop embedded in the track to the electric point motor.

 

Some are set manually as are any and all if the electric system fails.  A point bar is carried in all trams which is inserted into the tie-bar via a hole in the metal plate covering the mechanics.  The bar is then pushed (the rules specify pushed and never pulled) to change the points.

 

Some locations retain a single-blade point.  Those few which remain are at little-used crossovers and within depots.  A single swivelling point blade is moved by the tip of the point bar and the tram takes the route set.  In reality drivers will often kick the blade across which is not the official method.

Melbourne used to have a signal box in the city (which still stands as it is regarded as an historic structure) regulating the huge number of terminating and shunting moves at Swanston Street / Victoria Street.  Since the 1960s these moves have been progressively transferred farther north to the University which now has a semi-automatic three-siding arrangment under the control of the drivers but supervised by fleet operations remotely from their South Melbourne base.  The Melbourne box operated signals and directed drivers who still set the points themselves. 

 

These days signals are co-ordinated with motor traffic and under the management of VicRoads though trams in many cases have special white lights which when lit permit them to depart or to make an otherwise restricted turn.

[roythebus]

The Croydon system operates with induction apparatus under the cars.