Bi-directional line speed in "wrong" direction

[brad465]

Something I've seen on routes with the ability to travel wrong sided is the line speed is almost always lower where routing is as such. I suspect the main reason is lack of stopping distance with signal aspects being lower (2 aspect being most common), but wanted to be sure if this is the main reason, and/or are other common reasons involved?

Examples I know this to be the case are Tonbridge-Dollands Moor via Ashford on the SEML, which is 70/75mph in the wrong direction against 100mph for right routing. Another is the GWML between Swindon and Bath + Swindon to Bristol Parkway, which is 85mph vs 125mph for right routing at its top speed.

The SEML case though is to me confusing between Ashford and Dollands Moor, as both right and wrong siding are 4 aspect, but the wrong sided speed is lower so disproves my initial belief.

 

[The Lad]

Part of the northern ECML. BiDi has similar speed restrictions, at least in part because the signal spacing is longer.

 

[D1009]

There is a difference between full bi-di signalling and SIMBIDS (Simplified bi-directional signalling) which does not provide AWS for wrong direction moves. Signal spacing is probably the reason for different line speeds with the full bi-di.

 

[LNW-GW Joint]

Part of the northern ECML. BiDi has similar speed restrictions, at least in part because the signal spacing is longer.

SIMBIDS is deployed in several areas, including the ECML, and it does not have AWS fitted.
That may be another reason.

 

[MarkyT]

Another 'SIMBIDS' era trick to cut costs back in the 1980s was to only provide a single '3-aspect' distant signal for the reverse direction, when the parallel normal direction signalling had a full 4-four aspect sequence. The braking distance would thus be shorter, so could only support an approach speed lower than the normal direction. Reduced speed in the reverse direction was also claimed to be safer for track workers. Reducing the approach speed increases the warning time for 'unexpected' wrong direction movements. This is probably less critical today with increased green zone working.

 

[Senex]

The bidi section of the MML in the Leicester control area (as was) has had the same speeds in both directions since commissioning in the 1980s.

 

[edwin_m]

The bidi section of the MML in the Leicester control area (as was) has had the same speeds in both directions since commissioning in the 1980s.

That was and still is one of the few sections of main line with fully-fledged bi-directional signalling where every "right line" signal has a "wrong line" signal alongside. There were concerns about staff safety with trains arriving unexpectedly from the wrong direction and I'm not sure if the bi-di is available for use even today - certainly I've never been put wrong line in nearly 30 years of reasonably regular use.

A feature of bi-di lines is the wonderfully named PLOD - Patroller's Lock Out Device. Track patrollers walk the line facing oncoming trains and by use of this device they can inhibit the setting of routes that would result in wrong direction running while they are out on patrol.

 

[The Lad]

I have a memory that the MML BiDi was only used with prior notification, presumably because of this concern, which would limit its usefulness at times of service perturbation.

 

[Senex]

That was and still is one of the few sections of main line with fully-fledged bi-directional signalling where every "right line" signal has a "wrong line" signal alongside. There were concerns about staff safety with trains arriving unexpectedly from the wrong direction and I'm not sure if the bi-di is available for use even today - certainly I've never been put wrong line in nearly 30 years of reasonably regular use.

A feature of bi-di lines is the wonderfully named PLOD - Patroller's Lock Out Device. Track patrollers walk the line facing oncoming trains and by use of this device they can inhibit the setting of routes that would result in wrong direction running while they are out on patrol.

That was certainly true for most of it at first, though right from the start the section between Leicester station and Wigston N Jn was freely usable under BiDi, and I experienced and saw "wrong line" running on a good few occasions (including one interesting day when I was in a down HST that crossed to the up line at Wigston to pass a Birmingham-bound dmu on the down). I certainly experienced on a number of occasions other than Sundays (when it was frequently in use, but that of course was by arrangement for engineering works on the other line), but I think always either to get past a failed freight or because of signalling problems.

 

[louis97]

The bidi section of the MML in the Leicester control area (as was) has had the same speeds in both directions since commissioning in the 1980s.

Not since the line speed improvements though. The opposite to normal direction retained the same speeds.

That was and still is one of the few sections of main line with fully-fledged bi-directional signalling where every "right line" signal has a "wrong line" signal alongside. There were concerns about staff safety with trains arriving unexpectedly from the wrong direction and I'm not sure if the bi-di is available for use even today - certainly I've never been put wrong line in nearly 30 years of reasonably regular use.

Never traveled on a Sunday morning then? Regularly happens for the first 4 or 5 trains, i've been bi-di from Wigston (onto the slow then down main), to Kettering North a few times in the last few years.

 

[racyrich]

In a similar vein, are all points on bi-di lines locked then?

As opposed to just facing ones, since trailing ones become facing.

 

[edwin_m]

In a similar vein, are all points on bi-di lines locked then?

As opposed to just facing ones, since trailing ones become facing.

Where any of the various types of point machine is used, locking comes as standard whether the point is facing or trailing, goods or passenger.

 

[edwin_m]

Never traveled on a Sunday morning then? Regularly happens for the first 4 or 5 trains, i've been bi-di from Wigston (onto the slow then down main), to Kettering North a few times in the last few years.

I rarely travel on Sundays these days as I mostly travel for work. I used to do a lot more weekend travelling up until 2004 when family responsibilities intervened. Has the bi-di come into wider use in the last few years?

 

[alxndr]

Where any of the various types of point machine is used, locking comes as standard whether the point is facing or trailing, goods or passenger.

I know of one 63 machine without an FPL on a groundframe for the entrance to a yard (so solely freight, no need or chance of a passenger train being routed in there), so it is possible for point machines not to have FPLs, but certainly not standard.

 

[MarkyT]

Where any of the various types of point machine is used, locking comes as standard whether the point is facing or trailing, goods or passenger.

I know of one 63 machine without an FPL

Back when point machines were a white hot new technology, railways were able to save a few pennies by buying non-locked versions of the products from the various manufacturers for sites where the FPL was not legally required. The mechanisms were very similar, merely omitting a few components, so being simpler were probably a little more reliable too (theoretically). From the 1980s, maybe before, BR made it policy to only buy the FPL variants, and newer designs of mechanism such as the rail clamp lock and the HPSS under RT/Network Rail were developed with an FPL equivalent built-in by default from the start. With a typical machine lifecycle of around a decade before replacement by a new or refurbished example, most former non-FPL machines have been renewed by FPL examples under maintenance.

 

[QueensCurve]

Another 'SIMBIDS' era trick to cut costs back in the 1980s was to only provide a single '3-aspect' distant signal for the reverse direction, when the parallel normal direction signalling had a full 4-four aspect sequence. The braking distance would thus be shorter, so could only support an approach speed lower than the normal direction. Reduced speed in the reverse direction was also claimed to be safer for track workers. Reducing the approach speed increases the warning time for 'unexpected' wrong direction movements. This is probably less critical today with increased green zone working.

My understanding is that bidirectional signalling was opposed by those who inspected the track for fear that a train would come up behind them unexpectedly.

The issue was addressed by putting in a patrolman's lockout key in the lineside cabinets which would prevent bidirectional working.

To me, this is the wrong approach. The patrolman should have been able to lock out all train movements on the track he was patrolling by having a key to force bidirectional signalling on the other track thus creating his own "Green Zone".

 

[Tomnick]

My understanding is that bidirectional signalling was opposed by those who inspected the track for fear that a train would come up behind them unexpectedly.

The issue was addressed by putting in a patrolman's lockout key in the lineside cabinets which would prevent bidirectional working.

To me, this is the wrong approach. The patrolman should have been able to lock out all train movements on the track he was patrolling by having a key to force bidirectional signalling on the other track thus creating his own "Green Zone".

That'd take it from being an activity that could be carried out between trains whilst a normal service operated to being one that could (given the preference for daylight!) only be carried out on a Sunday morning. The ability to lock out wrong direction movements was a reasonable compromise to allow patrolling to continue safely without causing serious disruption.

 

[QueensCurve]

That'd take it from being an activity that could be carried out between trains whilst a normal service operated to being one that could (given the preference for daylight!) only be carried out on a Sunday morning. The ability to lock out wrong direction movements was a reasonable compromise to allow patrolling to continue safely without causing serious disruption.

Or between the peaks on a weekday perhaps (and additional weave time might be needed in the timetable).

 

[Tomnick]

Or between the peaks on a weekday perhaps (and additional weave time might be needed in the timetable).

On most main lines, especially nowadays, it'd be unachievable even between the peaks. I don't know how much red zone patrolling is allowed these days anyway, though. Where I was, it was all done under line blockages between trains.

 

[edwin_m]

The patrolman's lockouts I'm aware of were introduced during the BR era when red zone working was moreorless accepted as standard. Not sure what was done with more recent schemes - and I believe machine vision from the measurement train and similar vehicles has removed much of the need for track patrolling.

 

[Shrimper]

Even where full signalling and AWS/TPWS is provided on the bi-directional sections between Cheadle Hulme and Sandbach, speed is still limited to 60mph.

It's rarely used under normal circumstances as the service frequency in both directions is too high to enable it efficiently.

 

[Darbs]

I always used PLOD when Patrolling and Inspecting. If you didn't/couldn't use then you set up the appropriate lookouts for movements in both directions. Whilst there is a push to make everything green zone working it was always good to see trains passing over the track to give a view of voiding etc. Red zone working is not inherently unsafe as long as long as you do your job properly. In fact tour more likely to be more conscious of your safety when you know trains are running.

 

[CAF397]

With the resignalling works around Ordsall Lane Jn in manchester the Chat Moss lines because partly bi-directional. The Down Chat Moss is bi-Di in the Up Direction from Eccles all the way into Manchester Oxford Road. (Up Chat Moss is only bi-Di for one signal section in the Down direction).

The linespeed for the 'normal' direction is 75, and apart from a 15mph crossover at Eccles, Up direction running over the Down Chat Moss is also 75mph. Then both down to 50, and then 30.

 

[LAX54]

GEML Bi-Di in the Marks Tey / Colchester area is 70mph 'wrong' direction