Friday, 9 May 2014

What is... Automatic Train Operation? (And Why Do We Still Need Train Drivers?)

I'm often asked... sometimes asked... well, somebody asked me once: what do train drivers do? How hard can it be? Why can't it all be automated?

First thing: driving a train isn't like driving a car. The key difference is in braking. When driving a car, you brake on sight - you see something in the way, be that a pedestrian in the road or a car ahead slowing down, and you brake. When driving a train, unless you're going no more than about 20mph you haven't a hope of braking on sight, because trains brake much more slowly.

More starkly: a car doing 70mph can stop in 75m (plus thinking distance); a train doing 125mph takes about 2,050m to stop - nearly a mile and a half. So if a train driver sees an obstacle in front of him, he's going to hit it.

More than that, though, if the driver doesn't know where the signals are, where the speed restrictions start, or exactly where the stations are, he's not going to know where to brake. As a simple example, a fast train heading towards Coventry station from Birmingham will typically start braking before it gets to Canley station (which is 1½ miles out from Coventry). If it's been raining, there won't be as much grip, so the driver has to brake sooner. There's no sign telling the driver where to brake; the driver has to know.

The term given to this requirement is route knowledge: before a driver can drive a train unsupervised on any railway line, they must have sufficient route knowledge for that specific route. A typical, reasonably simple, route might require about 60 journeys back and forth before the driver can "sign the route", meaning he has been assessed as having sufficient route knowledge to drive a train unsupervised on that particular route.

Some drivers will only sign one or two routes; some drivers will sign hundreds. As an example, drivers based at Oxford sign the Great Western Main Line from London Paddington to Oxford, as well as the branch lines to Banbury and Great Malvern; in total, about 150 route miles. That may sound like a lot, but that means an Oxford driver can't drive a train to Swindon, Bristol or Newbury, all common destinations for a train from Paddington.

As a result, timetabling trains isn't just a matter of planning where the trains themselves go; it also involves ensuring that it's driven by a driver who signs the route. This isn't too hard to plan in advance, but it makes life complicated when things go wrong: if the controllers at Paddington want to send a train to Bristol and the only people around are Oxford drivers, they're stuffed.

So surely it would make life a lot easier if all the trains drove themselves automatically? In theory, yes, and we are at the stage where the technology is there that would allow almost all passenger trains to be driven automatically; this is generally called Automatic Train Operation (ATO). However, ATO does have its drawbacks: it's neither easy nor cheap to install the technology, and it involves modifications to both the tracks and the trains.

The modifications to the trains are particularly tricky: while it's easy enough to build trains with ATO equipment, retrofitting older trains with ATO equipment - even if they're just a few years old - can be a nightmare. It's not nearly as simple as, say, adding an after-market CD player to your car. A reasonable analogy would be converting a manual gearbox car to an automatic gearbox: it's technically possible, but for the amount of trouble it would be to convert the old one, it's often easier to just buy a brand new one.

Moreover, since one of the advantages of automating the driving of trains is more efficient braking, ATO requires every train on a route to be converted (or replaced) before there's any tangible benefit over human drivers. The capacity of a line is determined by how closely you can run trains together, and that's determined by how well a train can brake. When there's more than one type of train on a line, the capacity is generally limited by the worst-performing train on a given line.

For example, the line between Coventry and Birmingham has 7 passenger trains an hour in each direction, plus two extra that just run between Birmingham International and Birmingham New Street. Trains can (and do) run as little as 4 minutes apart, so in theory the line could take several more trains. The catch is that they'd all have to plod along as slow as the train stopping at all nine intermediate stations: currently the fast trains take just 20 minutes, while the stopping trains can take 35 minutes.

Now, ATO might manage to improve that a little, by safely allowing trains to be closer together; but it would require all the trains that run on the line to be converted. However, the trains that run between Coventry and Birmingham aren't self-contained: trains can start their day in Birmingham and end up as far away as London, Liverpool, Exeter or Edinburgh. I estimate there are 250 passenger trains which could, in the course of a week, run between Coventry and Birmingham. (Never mind freight trains, which are even more complicated.)

However, on self-contained networks with a dedicated fleet of trains, ATO can work wonders. Three London Underground lines have ATO: the Victoria line has had ATO from when it opened in 1968, and was in fact the first railway line in the world worked entirely by ATO. The Central line was converted to ATO in 2001, shortly after the introduction of a new fleet of trains. The Jubilee line was converted to ATO in 2011; in this case the existing trains were modified to work with ATO.

On the London Underground, the advantages of ATO can be seen very clearly. ATO's principal advantage is that it can stop the train at a station much more precisely: human drivers tend to be a bit cautious, since delaying people a few seconds is much better than crashing into something. Freed from human inhibition, the ATO system knows exactly where to brake, saving vital seconds.

Once the Jubilee line had been converted to ATO, the previous maximum frequency of 24tph (a train every 2½ minutes) was increased to 30tph (a train every 2 minutes). Now, 30 seconds may not sound like much, but that 30 seconds means a 25% increase in capacity (and, incidentally, a significant reduction in journey times as well).

The Central and Victoria lines operate at 33tph in the rush hours - about 110 seconds between trains - and are currently the most frequent lines in London; but such is the need for greater capacity that most other LU lines are being gradually converted to ATO: next will be the Northern line, which should be converted by the end of 2014.

That said, all the LU lines running under ATO still have drivers: although they can drive the train in an emergency, or when the ATO fails, their principal job is to open and close the doors. On the Docklands Light Railway (DLR), which has been completely driven by ATO since it opened in 1987, the doors are opened and closed by "train captains": they don't sit at the front of the train, but they are also available to drive the train in an emergency.

Truly unattended train operation, while technically feasible, often leaves passengers somewhat uneasy; the efficiency of ATO cannot be denied, but knowing that there's someone on board should everything go wrong affords a peace of mind - both for the operator and the passenger - that cannot easily be dismissed. Nonetheless, it does exist elsewhere in the world; Paris Metro Line 14 is completely driverless (and, incidentally, runs at 40tph - a train every 90 seconds!).

If you want to read more about the debate as to whether the London Underground should go "driverless", I highly recommend this post on London Reconnections.

What of Crossrail and Thameslink? In both cases the aim is for 24tph through the core. While many London Underground lines run at 24tph or more without ATO, it was decided to install ATO on Crossrail and Thameslink, with a brand-new fleet of trains brought in to operate the enhanced service from 2018. Due to the complexities of the National Rail network, ATO will only be used on the central core sections: on Crossrail, between Stratford, Abbey Wood and Paddington; on Thameslink, between London Bridge and St Pancras.

In a sense these are the only parts of the line which justify ATO, since further out the frequency of services is less; nonetheless, having part of the journey run by manual driving and part by ATO is an extra layer of complication, and it remains to be seen how it will work in practice. Crossrail, with only two branches to east and west, should work well. Thameslink, though, will have many more branches and has a much shorter core section; one late train could have significant ripple effects.

Thameslink will be served by a fleet of 115 trains (designated Class 700), which will be built by Siemens: of these, 55 are 12-car trains and 60 are 8-car trains. While the core will be capable of taking 12-car trains, there will be too many stations (particularly those on the Wimbledon loop) which cannot be lengthened beyond 8 cars. It will be interesting to see how the ATO system copes with different train lengths; all ATO operation in the UK so far is confined to a single type of train.

For Crossrail, 65 9-car trains (designated Class 345) have been ordered from Bombardier, with the option of a further 18 trains for future extensions. Although built by different firms, the two fleets will look quite similar internally: both will have fewer seats and lots of standing capacity, with full-width gangways between carriages to maximise capacity.

Of course, Thameslink is already served by a large fleet of about 110 4-car trains, most of which (the class 319s) date to the late 1980s and have plenty of serviceable use left in them. Once replaced by the new class 700 trains, these will be surplus to requirements for Thameslink and will be available for use elsewhere. Similarly, once Crossrail opens, it will displace a number of trains from existing services on the GWML and GEML.

The ideal solution is for these trains to move to another line to replace some of the oldest trains on the rest of the network, which can then be retired: this kind of "rolling stock cascade" means that more than one line benefits when new trains are introduced. There's just one slight problem: the class 319s are electric trains.

With the arrival of the new trains for Thameslink and Crossrail, the supply of electric trains will exceed the demand from electrified lines for them to run on. In the next post, I'll look at how electric railway lines work, and the benefits and disadvantages of electric operation; I'll also explain the programme of lines planned for "electrification" to rectify the imbalance.

One day, no doubt, automation will take over from human drivers in almost all aspects of driving trains. For most of the railway network that won't come soon; Crossrail and Thameslink are but the first tentative steps into automating the entire railway network. In the meantime, the cascade of rolling stock resulting from the new fleets for Thameslink and Crossrail will have more immediate impacts across the country: in the next post I'll begin to explain exactly where the ripples will be felt.

Previous post: What is... The Thameslink Programme?
Next post: What is... Electrification?


  1. That's a nice post, Dave. That is indeed a question that I had never thought to ask you. I look forward to your post on Electrification. Regards, Tom.

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  5. A much bigger differece between driving any rail vehicle and driving a car is, well, trains can't swerve.
    When driving any manually streered (road) vehicle (MSV for short), one also swerves on sight.
    When seeing something in the way, M.S.V drivers might not stop or slow down but rather swerve if there is room, stopping behind the other vehicle, for example, would be the next resort.
    On a road with more than one lane, it is possibile (and likely permissible) to change lanes anywhere along a road. It's my understanding that a tractor-trailer, for example, doing a typical highway speed, can change lanes within a shorter distance than it can stop. So if a M.S.V is going faster than another M.S.V ahead, it might actually overtake rather than reduce speed.

    But rail vehicles, be it trams or trains, can only change tracks at crossovers, which are likely few and far between.

    So need to know where to start braking is more critical with any rail vehicle (including trams) than with road vehicles (including buses).