Tram signalling

[Halsebee]

Whilst railways have a wide array of signals equipment and processes to prevent train running into each other or ending up travelling the wrong way on a track etc, a lot of trams seem to rely on purely line of sight driving. Why is this, and why, if safe for trams, can the principle not be applied safely to some slow speed rails lines? And what fail-safes are there to prevent trams ending up going the wrong way down a track?

 

[cool110]

The main thing to remember is that trams are much lighter and have track brakes for emergency rules. so their breaking distances are much shorter than a train at the same speed. So while it can as is also applied in other places it's not as useful with the speeds having to be even lower, leaving it mostly to be used only within depots or terminal stations. The main exceptions being on LU and HS1 where the rulebooks allow most signals that don't protect junctions to be passed at danger without needing to contact the signaller.

As for what stops trams going the wrong way, signals at junctions are ether interlocked with the points or separate point indicators are provided. In many cases trailing crossovers are sprung so that they always send a tram the right way unless locked in the other position.

 

[MarkyT]

The main thing to remember is that trams are much lighter and have track brakes for emergency rules. so their breaking distances are much shorter than a train at the same speed. So while it can as is also applied in other places it's not as useful with the speeds having to be even lower, leaving it mostly to be used only within depots or terminal stations. The main exceptions being on LU and HS1 where the rulebooks allow most signals that don't protect junctions to be passed at danger without needing to contact the signaller.

As for what stops trams going the wrong way, signals at junctions are ether interlocked with the points or separate point indicators are provided. In many cases trailing crossovers are sprung so that they always send a tram the right way unless locked in the other position.

Also single line sections, as in Croydon, have signalling to prevent conflicting movements occurring.

 

[Lemmy282]

As pointed out above trams are much lighter and as well as having wheel brakes also have magnetic track brakes and sanding equipment. They run mostly on roads with other traffic, so drivers have to be extra vigilant as a tram cannot swerve to avoid other road users. Line of sight driving has always been the case, even the first tramways had very little signalling, probably only for single line sections.
Sheffield Supertram was designed to be integrated with road traffic so the tram has priority at junctions, routes are set automatically depending on the destination of the tram and speeds over pointwork are low, so the drivers can see if the route is correctly set, and of course, being lighter vehicles they can accelerate much quicker than a train.

 

[Tim33160]

Manchester Metrolink works on line of sight with control signals at points/junctions - other than south of Timperley when the trams come under Network Rail on the single line towards Altrincham.
Historically the Manchester South Junction and Altrincham Railway ran out of money when it was built in 19th century so the last road over bridge was built at Timperley - with level crossings there after.
Today these are controlled by Network Rail signallers at Deansgate Junction box where two signallers work hour about fitting 10 trams an hour in each direction over the single line - with two level crossings - with the Network Rail single line of hourly Stockport - Chester diesels and assorted freight trains.

 

[blotred]

In Switzerland at least, some trams networks use a combination of "line of sight" and "fully signalled" operations, including the use of safety systems in the event of deviation from the shown signals.

Line of Sight is primarily used in cities, whereas fully signalled with the use of protection systems are used when the tram goes into the countryside or in certain tunnels.

For example, in Zürich Line 7 is line of sight except in the Schwamendingen tunnel where train protection and light signals are used. The train protection is quite basic (ie it's basically more of a train stop control if the signal is red, rather than speed control).

In Basel, BVB trams run in the city only, so are line of sight, and at complex points like Aeschenplatz or Barfüsserplatz, drivers must be vigilant to ensure the correct route has been transmitted by radio transmitter and the right route set*. I don't believe BVB trams are fitted with the Zugstop system.

Whereas BLT trams run in the city shared with BVB and the countryside, so they switch from Line of Sight to Fully Signalled (with train protection fitted at least on the newer Tango trams, not sure about the others) when they leave the city.

* Though during failures, I have seen drivers get out and manually set the points, or a member of BVB staff manually setting points using the manual lever.

 

[DeparturesBeck]

Manchester Metrolink works on line of sight with control signals at points/junctions

How are the points controlled in the city centre to avoid them moving with someone or something trapped between the moving parts? By the drivers?

 

[geoffk]

I always found Metrolink trams moved very slowly over facing points, often with a 5 mph restriction, e.g. at Shaw & Crompton coming into or leaving the bay platform, or approaching Newbold from Rochdale where the single line becomes double. Is this because tram points are not locked, as they would be on the railway, so could in theory move under a tram?

 

[507 001]

How are the points controlled in the city centre to avoid them moving with someone or something trapped between the moving parts? By the drivers?

The signalling system detects the tram on approach, reads the route code that the driver/the timetable has entered and sets the points accordingly. Tramway rules state that the points can only move as the tram approaches as the tram itself becomes a deterrent against people standing on the points.

A Points Position Indicator (PPI) is provided at all facing points (and some trailing points) to show whether the points are set correctly.

I always found Metrolink trams moved very slowly over facing points, often with a 5 mph restriction, e.g. at Shaw & Crompton coming into or leaving the bay platform, or approaching Newbold from Rochdale where the single line becomes double. Is this because tram points are not locked, as they would be on the railway, so could in theory move under a tram?

Into the bay at SHC is 10mph. Most facing points on Metrolink however have a 15mph speed restriction.

 

[geoffk]

Into the bay at SHC is 10mph. Most facing points on Metrolink however have a 15mph speed restriction.

10 or 15, then. Is this because of point locking?

 

[edwin_m]

The signalling system detects the tram on approach, reads the route code that the driver/the timetable has entered and sets the points accordingly. Tramway rules state that the points can only move as the tram approaches as the tram itself becomes a deterrent against people standing on the points.

A Points Position Indicator (PPI) is provided at all facing points (and some trailing points) to show whether the points are set correctly.



Into the bay at SHC is 10mph. Most facing points on Metrolink however have a 15mph speed restriction.

Are the points at the end of Market Street platform only set by the driver when they can see nobody is at risk? While the tram is approaching or stopped people can and do walk on the points, and if they were changed only as the tram started moving then they probably wouldn't be set before it reached them.

Line of sight operation is part of the definition of a tramway, and must apply if it shares road space with pedestrians or other vehicles anywhere except a railway-type level crossing. Because the driver must stop short of any obstruction, there is little point in providing signals as well, where they would only protect against tail-end collisions with other trams. Where there are junction or single line conflicts signals will generally be provided, but their logic and integrity may be more like traffic signals than the high integrity failsafe signals on the railway.

 

[507 001]

10 or 15, then. Is this because of point locking?

No, it’s usually due to a lack of flank protection.

Are the points at the end of Market Street platform only set by the driver when they can see nobody is at risk? While the tram is approaching or stopped people can and do walk on the points, and if they were changed only as the tram started moving then they probably wouldn't be set before it reached them.

Line of sight operation is part of the definition of a tramway, and must apply if it shares road space with pedestrians or other vehicles anywhere except a railway-type level crossing. Because the driver must stop short of any obstruction, there is little point in providing signals as well, where they would only protect against tail-end collisions with other trams. Where there are junction or single line conflicts signals will generally be provided, but their logic and integrity may be more like traffic signals than the high integrity failsafe signals on the railway.

No, MKT05P change on approach. You can only prevent them from changing by holding back from the loop a bit.

It’s worth noting that there are two types of line of sight signal on Metrolink.

1) TMS or Tram signals
2) Urban Traffic Control signals or UTCs.

The former is used to protect converging/diverging junctions and single line on segregated sections. These are subject to a higher grade of safety critical integrity and are usually interlocked with each other and any points that they protect, as with the big railway. They utilise axle counters for tram detection and will not give a proceed if the section that they protect is occupied, effectively creating small block sections.

UTCs are generally only found in street running areas, or areas where a segregated section crosses a road. These are tied in with and act more like traffic lights. They are generally not interlocked with points, although they obviously should be interlocked with each other. They use mass detectors for tram detection, but this is purely to tell the signal when to drop to a stop aspect. They can and and do therefore give proceeds even if there is a tram ahead, as they are generally only highlighting who has priority at a road junction.

At the delta junction for example, if a tram approaching from Market Street heading towards St Peter’s square stops across the junction, a second tram approaching from Piccadilly Gardens will still be able to get a proceed.

They can be told apart in a number of ways.

-TMS signals are a larger signal head.
-TMS signals are numbered, eg. CNK02S, OLD11S.
-TMS signal’s centre dots will not be illuminated until a tram is detected by the signalling system either on approach or by the driver pressing the ready to start button in the cab.

 

[miklcct]

What's the fastest operational tramway in the world which operates using line of sight? Are there any faster than 70 km/h?

Also, do Tyne & Wear Metro and Rotterdam Metro line E use railway signalling or line of sight? Both have level crossings and the latter shares track with trams as well.

 

[MCR247]

What's the fastest operational tramway in the world which operates using line of sight? Are there any faster than 70 km/h?

Also, do Tyne & Wear Metro and Rotterdam Metro line E use railway signalling or line of sight? Both have level crossings and the latter shares track with trams as well.

Nottingham used to be 80km/h but is 70 these days

 

[edwin_m]

Nottingham used to be 80km/h but is 70 these days

Croydon too. This limit is in the German BOStrab regulations, which many other countries have followed to some degree. This also means some vehicle designs aren't intended for use at higher speed either.

 

[507 001]

What's the fastest operational tramway in the world which operates using line of sight? Are there any faster than 70 km/h?

Also, do Tyne & Wear Metro and Rotterdam Metro line E use railway signalling or line of sight? Both have level crossings and the latter shares track with trams as well.

Manchester maximum speed is 50mph/80kmh. If it wasn’t for whatever regulation says 50mph (and of course the M5000 top speed), I reckon there’s places on our network where we could easily do 60+ on line of sight.

Tyne and Wear uses railway block signalling.

 

[dosxuk]

Nottingham used to be 80km/h but is 70 these days

I think Sheffield used to be 50mph (~80kmh) too - in the segregated section near Meadowhall at least - but I seem to recall that a PSR was applied?

 

[swt_passenger]

Manchester maximum speed is 50mph/80kmh. If it wasn’t for whatever regulation says 50mph (and of course the M5000 top speed), I reckon there’s places on our network where we could easily do 60+ on line of sight.

Tyne and Wear uses railway block signalling.

I would recommend taking the TW Metro completely out of any discussion about trams anyway. It has almost no similarities with tram systems, it has a completely segregated route way, and is regulated as a light rail metro system, not a tramway.

 

[507 001]

I would recommend taking the TW Metro completely out of any discussion about trams anyway. It has almost no similarities with tram systems, it has a completely segregated route way, and is regulated as a light rail metro system, not a tramway.

Correct.