Sunday, 31 July 2011

Thameslink ATO - I'm struggling

I'm struggling with the announcement, published in the latest issue of RAIL Magazine (No. 675 July 27th 2011), that Thameslink is intending to introduce Automatic Train Operation (ATO) on their core section, using the European Train Control System (ETCS), and to get up to 30 trains per hour per direction with it.   I'm wondering how they will do it.  RAIL reports that they will have station "dwell" times of 45 seconds and they are allowing 30s to arrive and depart, to give what we call a "platform re-occupation time" of 75s. This is, to be kind, very ambitious. In reality, it's a bit of a spin and, if they are think they will ever get 30 trains per hour, they are not being realistic.  Let's look at why.

First, we must make some assumptions.  We know the trains will be 12-cars long - that's 240m; and I doubt they will approach any of the inner area stations on the route at more than 35 mph, although some approaches might be less.

In considering the train's braking, we have to allow for rail conditions.  On metros that use ATO in tunnels, where the rails are dry, they can get a brake rate of 1m/s² but we have to allow for wet rails, so lets say 0.65m/s², to be safe.

Now, when calculating train throughput, you have to assume that all trains will run under clear signals.  If they don't, the service will slow down.  This means that the train approaching the station must not be shown a red or yellow signal, or the equivalent speed reduction command on the ATO system.  To ensure this, the rear of the train in front must be completely clear of the platform and of the starting signal, plus a safety distance, which in ATO circles is usually 50m.

In looking at how we do the calculations, a diagram might help.  It looks like this:

Here we see that Train 1 has left the station and, when its rear clears the 50m safety margin beyond the starting signal, the home signal behind it will clear and allow the following train (2) to run in unchecked.  Note that my diagram shows the front of Train 2 at 188m on the approach side of the Home signal as the point where the signal must clear.  This is because this is the closest Train 2 can get to the signal and stop at it.  If we left it later, the train would be automatically slowed down by the ETCS.

Now, the maths.  Our basic parameters are as follows:
Maximum train speed = 35 mph or 15.6m/s;
Train and platform length = 240m;
Signal safety margin 50m;
ATO brake deceleration rate = 0.65m/s²;
ATO brake distance (35mph to 0mph) = 188m;
Train acceleration rate = 0.9m/s² (generous but we can assume Thameslink will buy a powerful train);
ATO response time = 3s.

The calculation for the distance the train travels for platform re-occupation is:
188m (the home signal approach distance) + 50m safety margin at 35 mph; then the platform: 52m at 35 mph plus 188m braking to the stop.  Then, looking at the rear of the train, it starts and accelerates up to 35 mph.  This takes 136m.  The rear has to clear the rest of the platform (104m) and the Starting signal margin (50m) to clear the way for the following train which must be 188m on the approach to the home signal.

The time it takes to cover all this is (188m + 50m margin + 52m platform entrance @ 35mph = 18.6s) + (188m braking into station = 12s) + (136m acceleration to 35mph = 17.4s) + (the 104m remaining of the platform + 50m margin = 9.8s) to give a total of 57.8s.  Then we have to add in the standing time in the platform (the dwell) of 45s as suggested by Thameslink. This gives a total of 102.8 seconds between trains.  I've added 3s as an allowance for the ATO kit to respond to the signals and this gives 105.8 seconds.  I cannot decipher where Thameslink got 75s from.

Wonderful, you say.  This is equivalent to 34 trains per hour!  Plenty of room for more trains then. Well, no.  It's not as simple as that.  It never is, is it?  We have assumed that every train will arrive at the first home signal braking point at exactly at the moment the previous train has cleared the starting signal margin, but it never happens like that, as any commuter will tell you.  With trains coming into the central section of Thameslink from all over South East England, the chances of geting that sort of punctuality are zero.  A sensible, experienced operator will tell you that you should allow a large margin - at least 30% has been suggested by the UIC (the European-based Union of Railways).  This allows for time to change routes, variations in station stop time, higher speeds on outer sections of line, small variations in performance and minor delays.

The 30% operating margin will reduce our throughput to roundly 23 trains per hour.  Much more sensible and much more like what we will get.  Operators could do that, if they are on their toes and there aren't too many PIOTs (Passengers Ill On Train) incidents during the morning rush hour.

To go back to the Thameslink spin and their 75 seconds (I'm not sure where this figure came from but it must have been a rather grubby envelope), the problem is that it attempts to describe what's called the "signalled headway", not the "operating headway".  The signalled headway is the technical stuff we have calculated here but the operating headway includes the 30% margin and shows how frequently trains could actually operate.  They are quite different, as we can see.

Saturday, 30 July 2011

Diesel Page Update

I've updated the diesel locomotive page of Railway Technical Web Pages today. It has diagrams and descriptions of basic diesel locomotive technology.

This is the diagram showing diesel locomotive parts.  Each part is described in the text.

It's worth a look, even if you've seen it before.

Friday, 29 July 2011

Idling Diesels

People often complain about idling diesel locomotives in stations and railway yards.  They don't like the noise and they think that the emissions and fuel wasted should be reduced.  Like many things in the railway, there's lots of different issues so, in response to a recent question from Phillip, here's an overview of the problem.

Massachusetts Bay Transit Authority commuter train showing diesel-electric locomotive hauling passenger coaches.  The locomotive provides all the power for lighting, heating and air conditioning on the train.  The photo is by Michael Taylor.
The standard diesel locomotive is actually a diesel-electric machine as shown here and in the photo above.  The diesel engine inside the locomotive runs in order to drive alternators that generate electrical power for the train.  There are usually two alternators - one to provide power to drive the locomotive using electric motors on the axles, and a second to provide the locomotive and coaches in the train with "hotel power", like lighting, battery charging, heating and air conditioning.

A common reason for keeping a diesel locomotive idling is cold weather.  If the air temperature falls below 40 deg F, the engine will begin to freeze.  Diesel engines don't have anti-freeze so they have to be kept running to keep them warm.  Some locomotives are now being fitted with small diesel engines specially equipped with heating systems to keep them warm.

If the locomotive is providing "hotel power" for passenger cars, and the train is required to stand in a terminus or yard between trips, it will be necessary to keep the train warm to prevent it freezing (or keep it cool in the summer), so you have to keep the locomotive running to provide the power.  A way to overcome this is to provide a "shore supply".  A heavy duty cable has to be connected to the train to supply enough power to keep the heating/air con/lighting going.  However, not many yards and terminals have these and they are expensive to install and run.

As for fuel and pollutant savings in a modern locomotive, the Environmental Protection website describes the following example.  A reduction in commuter locomotive idling by even one hour per day per locomotive, together with modern ultra-low sulphur fuel fuel and a modern low-emission engine, could result in yearly carbon dioxide emission reductions of an estimated 800 tons, nitrogen oxides reductions of nearly 170 tons, carbon monoxide reductions of about 80 tons, particulate reductions of 23 tons, and sulphur dioxide reductions of 1-2 tons.

There's more information from MJ Bradley here.

Wednesday, 27 July 2011

Teach Your Children Railway Safety

Now the school holidays are here (again!), it's time to make sure your children are safe when they're out playing.  Network Rail has launched a campaign to show the terrible risks of playing on or near railway tracks.  A shocking, 2-minute video shows horrific injuries suffered by children who trespassed on railway tracks or tried to interfere with electrical equipment like overhead power lines or electric rails.

RAIL magazine has a copy of the video.  Every parent should see it and should teach their children about the dangers of messing with the railway.  It can be more dangerous than playing in the street.  Have you told your children?

Tuesday, 26 July 2011

High Speed Work

The report in the Journal of Commerce that the Norfolk & Southern Railroad in the US managed to upgrade a 100-mile section of track in an 8-day blockade, demonstrates just what can be done if there's a will and a way.  The journal reports that "They laid 29 miles of new track, resurfaced 69 miles’ worth, replaced three bridge decks and improved track signaling". Apparently, they needed 400 people working on the project.  I sometimes wonder if we have that many railway engineers available in Britain.

We don't know the exact circumstances of the project but, even if we could work at a quarter of that rate in Britain, we'd be doing better than we are now.  Network Rail, please note.

Monday, 25 July 2011

High Speed Rail in Brazil

I'm not surprised that the bidding for a new high speed rail line between Rio de Janeiro and Sao Paulo has been suspended due to lack of interest.  Anyone who thinks that you can build a new, electric passenger railway between two major urban areas across rugged and mountainous terrain for less than $80million a kilometre is dreaming¹.  In fact, it may cost even more if there are lots of tunnels.  The state bank BNDES (the state-owned development bank) suggested a price of about $60million per km.

The Latin American Herald Tribune, reporting the decision to suspend bidding, quotes the President of Brazil as saying, "I don’t believe the staff of the BNDES could have been so mistaken”.  Why not, Dear Sir? They were probably acting in good faith, but I suspect they ignored project, political or security risks and didn't count financing costs in the commercial money market.  What you might think the actual construction and equipment will cost and what a bidder, in the form of an international consortium, will charge in his price is quite different. In this case, 30% different.

This proposal for a Rio to Sao Paulo high speed rail link has been around for 10 years to my knowledge and it's always been regarded as a high risk project, with the stop-go politics of the region, local and international recessions and the construction and security problems of the area all worrying possible bidders.

If there is a consistent approach, political will at all levels and a commitment from the government to support the project, come what may, then you might get more interest from potential investors and bidders. Without it - no chance.

Footnote 1:  The Chinese quote a cost of $25million/km for their Beijing-Shanghai high speed line but they wouldn't include finance and risk.  The line was also very long, at 1302 kms, providing substantial economies of scale.

Thursday, 21 July 2011

"Kettled" Passengers

In the August 2011 edition of Modern Railways magazine, Alan Williams writes a great piece castigating the railway operators in Britain at the regular incidents of "kettling" passengers in trains due to failures and similar distruptions. Kettling is the word used by the police to describe how they contain people in street demonstrations and it seems that railway operators are doing the same to passengers, leaving them stranded for hours in trains with no information, no food or water and many of them standing.

Whatever happened to the "keep things moving" mentality of the railway? "Not any more, Guv", they will tell you. "We haven't got the authority/staff/safety case/equipment" (delete which not applicable). Why not? Surely the safety and comfort of passengers is top of the list and this includes safety from heat exhaustion, malnutrition, dehydration and physical collapse?

Alan, in his article, rightly suggests there needs to be a system in place for the timely evacuation of trains in such cases. There should also be training for staff on the ground as to how to move trains under failure conditions. The technology is available - it's not difficult to use it so, let's do it.

Wednesday, 20 July 2011

New Fleet on London's Victoria Line

There's a new fleet of trains on London Underground's Victoria Line. It's known as the 2009 Tube Stock and it's been built in England by Bombardier at their factory in Derby. A total of up to 43 x 8-car trains now provide the daily service in place of the withdrawn 1967 Tube Stock. Together with the new trains, a new Automatic Train Control (ATC) system, supplied by Invensys, formerly Westinghouse, has been installed to replace the original system. A great set of photos of both the new and old trains can be seen here.

The Victoria Line was designed and built for ATC and the first section opened in 1968. The 1967 Stock was the first new train in the world to be purpose-built for a new automatic railway. Now it has become history and, to tell the story, there's a new series on the history of the stock being written for Underground News. It's in preparation so, if anyone has a story to tell about the 1967 Tube Stock, please get in touch.

Tuesday, 19 July 2011

High Speed Rail in the US

There's been a lot of talk about high speed rail plans for parts of the US and there's a very useful map of the proposals on the Trains Magazine website. It includes the money allocated to each route.  It's not very big but I've uploaded a rather better version through the link here:

Not all the routes are "high speed" in international terms. Some are simply upgrades to existing routes to give 90-110 mph running (the taupe coloured lines) and others are described as "new conventional service" (green routes) or "upgrades to conventional service" (blue routes). In international terms, true high speed for trains means normal capability to run at over 125 mph (200 km/h).

There's a series of articles on the High Speed Rail situation in the US in Trains Magazine.

Wednesday, 13 July 2011

Level Crossings

There's an interesting article about "Airtrack" in RAIL magazine No. 673 by Christian Wolmar, one of Britain's leading rail journalists.  "Airtrack" is the name given to the scheme to provide a rail link to Heathrow Airport from the southern side.  It would run from a junction with the existing rail route between Staines and Chertsey into the airport.

The link is only 4 kms long and it uses an existing railway route for part of its length but the cost is estimated at £673million.  Why so expensive?  That's over £168million a kilometre - for a bit of tunnel and the rebuilding of an existing route?

His article can be read online here: How Airtrack was derailed.

There's a few things in it that are quite controversial.  The first is the cost, as I mentioned, but another is the problem of level crossings.  There are a lot of them - 15 all together - and they cover the three routes that would be used by the new service, from Waterloo, Reading and Guildford.  Christian writes that he was surprised when Phillip Hammond, the Secretary of State for Transport, "had a rant about level crossings".  I'm not.  They are a nuisance and dangerous because they cause frustration when car drivers have to wait long periods with nothing apparently happening, so drivers take chances with them, risking their own lives and those of train crew and passengers.  It's time there was a programme to remove them at the earliest opportunity.  It's expensive but worth doing.  This route would have been a good place to start.

Tuesday, 12 July 2011

The Big Issue

What is the biggest issue for the British railway system today?  Is it the new high speed line, HS2?  Is it capacity?   Is it on-time performance?  Is it the cost of running the railways?

What do you think?

Monday, 11 July 2011

The ATC Bump

Many metro systems use Automatic Train Control (ATC), where the train is driven automatically and has built-in collision prevention called Automatic Train Protection (ATP). The ATP part is the safety system, while the automated driving control, called Automatic Train Operation (ATO), sits on top of it and drives the train much like a driver would.  What ATO won't do, unless it is specially programmed to, is fine tune the stopping to make it comfortable for the passengers.  This leads to a phenomenon which I call "the ATC bump".

As one of my students pointed out to me this afternoon, the ATC bump is what you feel when the ATC controlled train stops.  It stops hard with the brakes on and there is very little adjustment to reduce the jerk you feel at the stopping point.  If you like, you could say that the jerk is not limited.  Well, it should be.  "Jerk limit" is incorporated in most traction and braking systems, the technology is available and, although it requires some effort to get it to work well, it can enhance passengers' comfort.  It also helps to demonstrate to taxpayers' that their money has been well spent.

All the ATC operated lines in London (the Central, Jubilee and Victoria Lines) suffer from this problem.  In the case of the Victoria Line, it's rather annoying, since the old fleet (the 1967 Tube Stock) has recently been replaced and, not many years before its replacement, it was given a modification to incorporate a smooth stop.  The new fleet (the 2009 Tube Stock) that has replaced it has brought back the ATC bump.  What a shame.

Sunday, 10 July 2011

Braking Curve

In railway engineering, you will sometimes hear talk of a "braking curve", often in connection with train performance, platform re-occupation times or signalling. A braking curve is used to calculate how long it will take a train to stop from a given speed. It can be used to determine both service and emergency braking distances and it can give braking times, if needed. Here we look briefly at the braking curve and what it means.

The braking curve is the shape formed on a speed/distance chart by a train as it slows down from normal speed to a stop.  A typical curve looks like this:

The curve begins when the driver applies the brake. The brake system take a few seconds to build up to the required braking rate (the "feed up" time) and then the train begins to slow down.

With a constant brake demand, as selected by the driver, the train slows down more rapidly as the speed falls. This is because, at the lower speed, the train has less energy to dispose of. If the brake is left on at the same level all through the stop, eventually the curve will get steeper and steeper until it ends vertically at the stop. If this is allowed to happen, the train will stop with a sharp bump and a lot of coffee will be spilt. To prevent it, a skilled driver will ease off the brake as the speed falls and this will allow him to stop the train gently. The effect of this can be seen on our curve as it nears the stopping point.

Our drawing also shows an "equivalent straight line" curve. This is a simple way of showing the stopping distance that we can expect a train to cover, given an equivalent deceleration rate. It can be used to calculate stopping distances for rough signalling calculations, for example, although today, computer programs make accurate and detailed calculations simple.

Saturday, 9 July 2011

The 3-minute Rule

It's time the railways in Britain got to grips with what passengers expect in timekeeping.  The present 10-minute threshold described as "on time" for long distance trains and the 5-minute one for local trains is ridiculous.  It is derided by passengers as a "lie" and "idoitic" and they're right.  When a train is advertised as arriving at 10:07, it should get there at 10:07.  10:16 is not "on time", it's 9 minutes late and we travellers all know it, regardless of what the railway company or the Department for Transport might say.

If there has to be some leeway in train timekeeping for performance monitoring purposes, there should, logically, be a 3-minute rule for all trains.  To understand why, we need to understand how a railway produces its product.  We have to get, at least, the basics - what the railway offers as a service and how it makes that offer work.  We should start by looking at the timetable.

A railway is a service provider.  It provides a travel service.  It provides the service by producing a stream of moving packages called trains, which are used to transport people along a production line called a track. The intervals between the the moving packages, the trains, are decided on (usually) according to the number of people who want to travel along that particular route at that particular time.

Since most railways don't have so many prospective passengers that they need to provide trains every few minutes they make it easier for passengers by writing a timetable¹.  The timetable sets out the times trains are due to appear at each calling point.

Now, there are limitations on the number of trains you can run along one track in one direction.  The limits are set by the trains' ability to stop safely.  Since trains are heavy, long and often move at quite high speeds they need lots of room to stop.  In fact, most trains need about 10 times the stopping distance needed by your car on the road.  So the intervals between trains are set for safety reasons, in much the same way as the wise car driver does when he leaves enough room between himself and the car in front in case he has to stop quickly.  Train drivers do the same but they are guided by signals.

Signals are provided so that trains drivers can keep their trains a safe distance apart.  Signals provide guidance on the state of the line ahead so that the driver can adjust the speed of the train accordingly. On most major routes in Britain, the signals will allow trains to run at about 3 minutes apart, that's 20 trains an hour.  In reality, it's slightly fewer trains per hour than this because a margin is allowed for different driving techniques, longer than normal station stops, different types of trains and variable local conditions.

So, our railway production line can send packages, our trains, along the line at 3-minute intervals and this is our basic performance criterion - a 3-minute service interval, or "headway", as we on the railway call it.  If we are going to judge our performance properly, we should examine our production line, our train service interval, our so-called headway.  If our railway is going to perform according to its capabilities, we should regard any deviation from our 3-minute headway, such as late running, as wrong, because it prevents our train "packages" from passing along our production line at the correct, 3-minute intervals.  Put another way, late running reduces our production capability and therefore reduces our performance.

So, any train that runs more than 3 minutes late is occupying the time² belonging to another train and we have therfore lost a unit of production.  This is how we should judge our performance - on our time within 3 minutes.  Any other value judgement is false, as it ignores the simple unit of production that is the basis of any railway operation, the train headway.

Footnote 1:  Generally, if a train service runs at less than 10 minute intervals, a full, published timetable isn't necessary.  Of course the railway will produce its own "working" timetable to ensure that trains are run at the correct intervals but it will give the passengers a service frequency of, say, "a train every few minutes" or "a train every 7-8 minutes", so that passengers know what to expect.
Footnote 2:  We call the time a train occupies a section of line as its "path".  Trains are given a "timetabled path" and many railways use a graphical format for timetables to show how the train paths fit on a time plan.

Friday, 8 July 2011

Why did Bombardier lose Thameslink?

Basically because of their financing.  The Thameslink deal was based on financing the order as well as building trains.  Their train-building skills are as good as Siemens in most respects but they do, according to The Daily Telegraph,  have a lower credit rating than Siemens.  This means that the finance behind their offer will be more expensive than Siemens because their cost of borrowing is higher.  The cost is so much more that it amounted to £700million over 30 years.

I know little about corporate finance but that seems a lot of money.  I wonder also if Bombardier's own risk profile was skewing their contract terms, and that these made them less competitive than Siemens.

See more here: