The Status Quo.
Trains are a nineteenth century invention. They use tracks with a gauge that is based on the wheel spacing of a Roman chariot. (The Romans made the best roads but they fell into disrepair when the Romans left. All later wheeled vehicles had to have the same wheel spacing as the ruts that had developed in the Roman roads. When rails were introduced, the coach builders who built the trucks used the wheel spacing that they were used to.)
Locomotives were expensive to build in the 19th century so they were made large and powerful. There was little cost saving in making them smaller. One large locomotive could pull a large number of unpowered coaches or trucks. This arrangement continued with steam trains until fairly late in the 20th century. The concept of the long train of many coaches became so well established that hardly anyone has considered that another way of using the tracks is possible.
Trains Cannot Stop Quickly
Early trains had very poor brakes and the trains used today are not much better. Research shows that a passenger train using maximum safe braking can only stop at a rate of around 1 ft per second per second. (1/32.2g) 1g = 32.2 feet per second per second.
The braking efficiency of road vehicles in Britain is measured as a percentage where 100% is a deceleration of 1g. A road vehicle's brakes must be at least 50% efficient by law. Most road vehicles can decelerate with an efficiency of 80% or 0.8g. A Formula 1 car can decelerate at 2g or more.
These rates of deceleration have a large effect on the distance it takes to stop. The metric figures are direct conversions from the Imperial figures. 1,292 yards is just short of 3/4 of a mile and 5166 yards is nearly 3 miles.
|F1 Car||2g||60 mph||20 yards||120 mph||80 yards||96.5 kph||18.3 metres||193 kph||73.3 metres|
|Car||0.8g||60 mph||50 yards||120 mph||200 yards||96.5 kph||45.7 metres||193 kph||183.2 metres|
|Bus||0.5g||60 mph||80 yards||120 mph||320 yards||96.5 kph||73.1 metres||193 kph||293.2 metres|
|Train||0.031g||60 mph||1,292 yds||120 mph||5,166 yds||96.5 kph||1.181 km||193 kph||4.724 km|
The stopping distance is the critical factor that decides the minimum safe spacing of vehicles. Formula 1 cars, ordinary cars and buses can stop easily within the distance that the driver can see ahead but train drivers cannot. A bus or car driver will assume that the vehicle in front cannot stop much more quickly that he or she can so the following driver usually drives at less than the stopping distance behind the vehicle in front. Train drivers have no choice. Trains are usually spaced at much greater distances than the stopping distance. This is obviously very wasteful of track space.
It is not practical to improve the braking efficiency of conventional
trains because the track could not withstand the force needed
to stop a train much more quickly without being damaged. The energy
that needs to be dissipated when stopping a vehicle is proportional
to the square of the speed and half its weight or mass. A typical
train weighs around 400 tons. A typical bus weighs around 8 tons.
A typical car weighs one ton.
Shorter Trains or Single Rail Coaches?
It is clear that the rate of deceleration for a train could be improved significantly if it weighed a lot less than 400 tons. For example, if a 12 coach train was split up (without a standard locomotive) into 12 separate self powered coaches weighing around 30 tons each, the deceleration could be increased to 12 times the rate of a standard train without damaging the track. (This is assuming that an emergency stop by a 400 ton train does not damage the track now.) If railway coaches did not have to be built to withstand the compressive forces that arise in the event of a crash, they could be built much lighter than 30 tons. Then it would be possible to have brakes that grip the track. These would be one-sided versions of the calliper brakes fitted to bicycles. Track brakes would have rollers to prevent wear on the inside of the track to maintain the gauge. If the weight of a rail coach could be reduced to around 12 tons it would be possible to achieve a deceleration rate of 0.5g to 0.6g without damaging the track.
Track Wear and Power Consumption
Wear by a rolling wheel is approximately proportional to the sixth power of the axle weight. In other words a coach that weighs 30 tons causes 64 times as much wear as a coach weighing 15 tons. The electric current drawn by an electric train is roughly proportional to its weight when travelling at a constant speed on the level. The power lost in the electrical distribution system is proportional to the square of the current drawn. The power lost in the distribution system is reduced to one quarter if electric rail coaches are reduced to half their current weight.
A Possible Future for Trains
From the point of view of the commuter it is much more preferable to have a single rail coach that leaves every five minutes to a 12 coach train that leaves hourly. Terminus rail stations would have to be rebuilt so that all tracks are loops. There would be no need for long cul-de-sac platform arrangements with single rail coach vehicles. Most of the current signalling would become unnecessary because the points would be changed by a computer in the driver's cab. The computer's data would be updated frequently from a master computer using the mobile telephone network. The mobile telephone network electronics can locate a mobile telephone within a 50 metre radius. This information can be sent to the rail coach computers to ensure that correct spacing is maintained. The driver would be able to stop the rail coach well within the distance that he or she can see ahead. This would prevent accidents like the one that occurred on 28th February 2001 at Selby/Great Heck in Yorkshire (where a Land Rover fell onto the track) and the accident that occurred at Nocton near Lincoln on 28th February 2002 (where a van fell onto the track). The ability to stop quickly would permit rail coaches travelling at 120mph to be spaced 15 seconds apart while allowing a good margin of safety. The track resource would be used more effectively and efficiently and would cost a lot less in maintenance.
A Go-Anywhere Service?
A further gain in efficiency would be the ability to re-route rail coaches to suit a wide range of situations. The earlier approach (supervised by Lord Beeching) was to cut down on unprofitable lines to attempt to improve the overall profitability of the service. This has resulted in a general shrinkage of the rail service that cannot be easily undone. It has been shown that buses cannot provide a satisfactory replacement for trains. With the clarity of hindsight it can be seen that in almost all cases where a Beeching cut rail service was replaced by a bus service, the bus service was eventually discontinued. The result was that the business that the rail service had gained from the "unprofitable" feeder services for the "profitable" services was just thrown away. The rail service became even more London centred than it had been previously. If some of the cut lines were restored it would be possible to run rail coaches on routes like Cambridge to Bedford. Disused railway "Halts" could also be restored so that the rail service would be more accessible in rural areas. This would be quite practical if a rail coach could stop and start as quickly as a bus.
An Automatic Stopping System
There is a proposal in Britain to make trains safer by using a method of stopping trains automatically if the signals are at red. It is estimated that it will take until 2008 to complete the installation of the system at a cost of three billion pounds. Even when the automatic stopping system has been installed in every train it will not prevent the sort of accident that occurred at Great Heck on February 28th 2001. The existing and planned train control systems assume that the only obstacle that may be encountered by a train is another train that is not derailed on the same track.
The two reasons for having any sort of automatic stopping system
1. Trains are still using what is basically 19th century technology. In other words, the brakes are so poor that a driver cannot stop a train within the distance that he or she can see ahead.
2. A driver may suffer from sleepiness or otherwise lose concentration and fail to observe stop signals.
Electronics Can Help Make Existing Trains Safer with Television
Alongside most railway tracks are a series of posts. These may be telephone poles or the supports for the overhead electrical power supply cables. These posts are close enough to the track so that anyone who was on one of them would have a very clear view up and down the track for half a kilometre or more in most cases. A television camera could view the same length of track quite easily - particularly if it had a zoom lens fitted.
Ordinary television cameras are very cheap nowadays and the humble web camera is even cheaper. Mobile phone technology has reached an advanced stage so that it would be possible to use the GSM system to transmit slow scan television pictures from the cameras to the train drivers and the signalling staff quite easily. JPEG compression could reduce the bandwidth needed to a low enough figure to suit existing GSM channel widths. A slow scan system would enhance the cameras' sensitivity in dim light.
Seeing Ahead by TV
I suggest that a driver's look-ahead video screen is fitted into every train driver's cab. The screen would normally display the next (say) nine sections of track in sections of the screen. The identification of each section would show the driver the sequence of views from the closest to the most distant. The driver could select any section at will to enlarge it temporarily to the full screen size. The driver could also use the camera's zoom lens (using the GSM system to control it) to see a more distant view more clearly. The same information could be relayed to the signalmen covering the same track sections.
Infra Red Could Help
If the cameras have an infra red sensitivity as well as normal (human) vision, it would be possible to identify objects in view that were warmer or cooler than the track more easily. (A false colour version of the view could easily be arranged.)
A Frame Store to Detect Changes
A further addition would be a frame store that could be used to compare the standard view with the view currently showing. Any changes in the view would be a reason for an alert or warning that something unusual has occurred.
This system could work on its own in daylight in the absence of fog. It would enable drivers to see that the track in front of them is clear for several miles. This alone would mean that nearly all accidents that might occur in daylight would be avoidable. This would at least halve the likelihood of serious accidents occurring. In practice, the likelihood of accidents occurring is higher during daylight hours because more trains run during the daytime and there is a greater possibility that a road vehicle is stuck halfway across a level crossing.
A further improvement that would be fairly cheap to implement is radar. Low power radar is used extensively (and relatively cheaply) for road speed traps and the control of traffic lights.
Traffic light radar could be used to monitor any changes that occur within its range on a section of railway line. It would also work well in dark tunnels. Most of these changes would be caused by trains so the information thus gained could be relayed to signalmen to check the progress of scheduled train services. If a change is observed when a train is not expected, the signalling staff would know that something unusual and possibly dangerous has occurred. This could be anything from an animal or some other obstruction that has appeared on the line or that a landslip has occurred. The speed trap type of radar could be used to check that passing trains are travelling at the correct speed. For practical reasons it would be triggered by approaching trains (because trains are usually long vehicles). This would be the opposite of that used for road speed traps that check the speeds of departing vehicles.
As GSM is a two-way system, it could be used to relay snapshot views taken by a digital camera mounted on the front of the train. The camera could be triggered by the reception of a radar signal from a proximity (traffic light) radar transmitter mounted on a rail signal gantry. Such pictures could be used to check the visibility (or otherwise) of the rail signals as the train approaches them.
There are several rules that can be used to reduce or eliminate the problem of driver sleepiness or inattention. I suggest that the first one must be included.
1. If a train driver feels sleepy he should be able to report the fact by mobile phone without having to worry about his job or being paid for his shift. A relief driver should be found to replace him at the next safe stopping place. No driver should ever be sacked for reporting sleepiness. If no accident occurs, a driver who passes a red signal without reporting sleepiness beforehand should be transferred to a lower risk job at a reduced salary.
2. There must always be two (or more) rail staff on every passenger train. The other person could be a guard, a ticket collector or a dining car attendant. The person concerned should be instructed how to stop a train quickly and safely. (There have been true stories about a passenger who has landed an aeroplane safely when the pilot became disabled. Stopping a train would be much easier.)
3. The drive power must be reactivated every (say) twenty seconds, otherwise the engine shuts down. If the train starts to slow down without an apparent reason, the other employee would be duty bound to find out why. An intercom connected to the the driver's cab would enable a quick check to be made. If the driver does not reply immediately, the other staff member could use a mobile phone to report the situation very quickly. A member of the train staff who travels on the same route regularly would be likely to realise that something was wrong if the train started to slow down where it had not done so previously. If two reactivations are missed, an automatic message can be sent to the signal control centre.
4. The nine (or more) view video display could be equipped with a touch screen that would cancel the view of each section of track after it had been traversed. A failure to cancel the view would be treated as if an engine reactivation had been missed.
5. A driver should report his or her status and position by phone whenever asked to do so by the signalling staff.
6. The driver should be tested for his or her reaction time periodically to check that he or she is alert. This could be a visual or audio signal that has to be cancelled by pressing a button.
7. A video camera in the cab may well discourage a driver from falling asleep. A driver is less likely to fall asleep with "Big Brother" watching.
A Complicated System
The British automatic train stopping system when implemented would have to be operated so that a train would be stopped within the appropriate safe distance for the train in question - assuming that it was travelling at the correct speed. The correct permutation of train types, normal running speeds, safe stopping distances and signal positions would have to be chosen by a computer in the signals control centre - when a red signal is passed. The cost and complexity of the planned system is mainly designed to deal with just one human failing - sleepiness.
Would a TV System be Cheaper?
I cannot say how much it would cost to implement the TV and/or radar systems but I doubt if they would cost more than three billion pounds. Even if these systems cost more, they would be much more effective and could be implemented much sooner than 2008. They would overcome most of the limitations imposed by 19th century technology and driver sleepiness.
Trains are currently controlled by signals that are not vastly different from the signals used 100 years ago. The mechanical links to signals have now been replaced by electric cables and motors, and electric lights have been added. The signals offer three indications - Go, Caution and Stop. Two successive signals may be used to provide a small amount more information than a single signal but this relies on the driver remembering the status of a signal that he or she has passed some time earlier.
Signalling largely relies on anticipated events. As a train passes over a track section its wheels and axles connect the two rails together electrically. This connection sends a signal back to the signalling staff to indicate the position of a train. It cannot give any other indication about the state of the track. In other words the amount of information communicated between the signalling staff and the train is minimal in both directions.
If GSM is used there can be several sorts of information transmitted. Firstly, the states of (say) five signals can be displayed on the drivers look-ahead screen. These can be represented as small images of the actual signals on one side of the screen. The images would move downwards as the train progresses. A fixed pointer would show the relative position of the train with respect to passed and upcoming signals. This would be particularly helpful at the entries and exits of large stations and junctions where there are a lot of parallel tracks and big gantries crowded with signals. Sometimes drivers cannot be sure which signal applies to which track. Images of the signals that only apply to the train that receives them could save a lot of confusion.
Voice and Text messages
This basic signal state information could be supplemented by voice or text messages relating to any aspect of the train's operation. The driver could be told to slow down because of a delayed train ahead or to speed up to catch up a bit on lost time. If a different platform to the usual one has to be used at the next station, the driver can be warned so that the message can be passed on to the passengers and other staff on the train. The driver could also use the GSM phone system to report any problems with the train or track to the signalling staff in an emergency.
The GSM system uses ten frequencies in a pseudo random order to provide security and to ensure good communication with a mobile phone. The frequency hopping overcomes the problem of a lost signal due to a dead spot where reflected waves at one frequency cancel each other. The audio signal is compressed in time digitally to allow ten different phones to share the same channels. The base station has to tell the mobile phone which channel to use next on a continuous basis. However, there is always a time delay between the base station's transmission and its reception by the phone. All the time that the phone is switched on it is interrogated periodically by the base station with a request for its identity. The time it takes for the base station to receive the identification signal after it has requested it is noted. Information about frequency changes can be sent to the phone in advance to compensate for the time delay between the base station and the phone. The time delay indicates to the base station how far the phone is away from it. Normally a mobile phone will be interrogated by two and maybe three base stations. Each base sation will know how far away the phone is. The information from two or more base stations can be used to locate the position of of a mobile phone within a 50 metre circle. This information can be relayed to the signalling staff to show a train's progress.
A Dedicated GSM Network for Railways
The present GSM phone networks in Britain leave very little room for expansion. I envisage a dedicated GSM network for the rail service. The coverage of the base stations could be directional along the tracks to make it simpler to find a suitable frequency band for the special network. GSM base stations use very low power transmitters to cover relatively small areas. The power needed for the rail network base stations could be very much lower than for a normal telephone network. The train could have a much more sensitive antenna than is used on a normal mobile phone. On the other hand the power used by a train's mobile phone could be somewhat higher than that provided by a portable mobile phone. (There would be no need to depend on a small and portable battery supply.) These two factors in combination would make it easier to find suitable sites for base stations along a length of track.
The two approaches in this essay offer ways to make a train service safer. The single rail coach idea would make it possible to to reduce the need for timetables on many lines. If a traveller could be sure that another rail coach would appear within a few minutes, there would be less incentive for him or her to use a car for the journey. Rail coaches could be run very closely spaced on busy commuter routes to avoid overcrowding. It would be easier to make more efficient use of the existing railway tracks because there would be no need for a commuter train to wait until an express train had passed on a shared section of line. Single rail coaches would cause much less track wear so maintenance costs would be lower.
An article that includes much of the above text appeared in the November 2001 issue of Electronics World. This version includes feedback from train drivers who read that article.
wilf dot james at ntlworld dot com