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.

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.

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.

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?

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.

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.

"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.