15march2007

Rail safety and rail privatisation

Privatisation of the state-owned British railway system was com-pleted in 1997. The following 6 years saw four serious fatal train accidents, leading to 49 deaths. These were the train collisions at Southall in 1997 and Ladbroke Grove in 1999, each caused by trains passing red signals, and the derailments at Hatfield in 2000 and Potters Bar in 2002, each caused by defective track. Has safety been compromised by the sell-off of the railways? Andrew Evans looks at the evidence and asks has privatisation led to more accidents?

a safety experiment, so we have observational, not exper-imental, data by which to judge the safety consequences of privatisation. Th e problem with such data is that simple comparisons of accidents or accident rates before and after privatisation do not provide good estimates of the eff ect of privatisation, because some changes be-tween the before and after periods could be expected to occur anyway. Th erefore, the statistical task is to pro-duce estimates of the numbers of accidents and fatalities that could have been expected in 1994–2005 if BR had continued—the “counterfactuals”—for comparison with the numbers that actually did occur.

Two factors commonly taken into account in inter-preting ‘before and after’ observational accident data are (a) changes in the scale of activity giving rise to accidents and (b) changes in accident rates due to general trends or other safety measures. Scale is here taken into ac-count by assuming that the mean numbers of accidents are proportional to train-kilometres; the eff ects of other safety measures are taken into account by assuming a time trend in accident rates. Accident rates have fallen substantially over the long term.

Accident data

Railway accidents are classifi ed into three types: train accidents, movement accidents and non-movement ac-cidents. Train accidents are those in which a train is damaged and casualties may occur; movement accidents

In 1994 as the fi rst major step in the privatisation of the railways, Railtrack took over the track, signalling and infrastructure from the state-owned British Rail (BR). At the same time, all BR’s other activities, includ-ing train operation and track maintenance, were divided into about 100 separate units, and these were privatised, one by one, over the following 3 years. Railtrack was ini-tially publicly owned, but was privatised in May 1996. Because of the four serious accidents in the following 6 years, many journalists, railway professionals and mem-bers of the public believe that the government’s objec-tive of maintaining safety during privatisation was not achieved, and that safety got worse. Is that belief justi-fi ed? Do the statistics back it up?

It was clear from the start that privatisation could aff ect railway safety, and that safety would require care-ful management. Infrastructure provision and train op-eration were to be separated for the fi rst time in Britain, and the safety responsibilities of the many diff erent new railway organisations might be ill defi ned. Safety-critical information might be attenuated across organisational boundaries—the so-called “interface risk”. New compa-nies with little previous experience of safe railway op-eration might enter the industry. Changes in working practices would almost certainly follow.

What in fact did follow? Here we look at the safety record of the privatised railway in the 12 years since pri-vatisation, using railway fatal accident data from before and after privatisation. Privatisation was not designed as

It was clear that privatisation could affect rail safety. Privatisation was not designed as a safety experiment.

16 march2007

are those in which a person is killed or injured due to the movement of a train but the train itself is not damaged, such as when a person is struck by a train; non-movement accidents are other fatalities or injuries on railway property.

Table 1 shows the numbers of fatal ac-cidents and fatalities (excluding trespassers and suicides) on the main line system in the 39 years from 1967 to 2005, derived from HM Railway Inspectorate reports. We treat 1967 as the beginning of the modern era on the railways in Britain—it coincides approxi-mately with the end of steam traction. Table 1 shows that there were a total of 2295 fatal accidents, causing 2687 fatalities. Th e major-ity of fatalities occur not in high-profi le fatal train collisions and derailments, but in largely unreported movement and non-movement ac-cidents, most of which are single-fatality ac-cidents.

Th ere were 80 fatal train collisions, derail-ments and overruns in the period 1967–2005, with 320 fatalities, giving an average of four fatalities per accident. Th ese account for 3.5% of the fatal accidents and 12% of the fatali-ties. Th e distribution of fatalities in such ac-cidents is skew: most accidents have a small number of fatalities, but a few are much more serious. Th ere were three train accidents with more than 15 fatalities in the period: at Hither Green in 1967 with 49 fatalities, Clapham Junction in 1988 with 35 fatalities and Lad-broke Grove in 1999 with 31 fatalities.

Th e other important type of train acci-dent is collisions between trains and road vehi-cles, mostly at level crossings, but occasionally elsewhere. Th ere were 176 such fatal accidents in the 1967–2005 period, with 249 fatalities. Most of the fatalities are road vehicle occupants and most accidents involve small numbers, but a few are more serious, such as the collision at Ufton Nervet level crossing in 2004, in which six train occupants were killed as well as a car occupant. Table 1 also has a residual miscel-laneous category of “other” train accidents. We disregard these in the analysis; they are too few to aff ect the conclusions.

Fatal movement and non-movement accidents

Figure 1 plots the numbers of fatal movement and non-movement accidents per million train-kilometres for each reporting year 1967–2005. Th e full data points are for the British Rail (BR) era up to 1993–1994; the empty points are for the privatised era from 1994–1995. Th e full fi tted curve is the mean number of ac-cidents per million train- kilometres, estimated from the 27 BR data points on the assumption that accidents occur as a Poisson process with mean proportional to train-kilometres, and with an exponential trend over time. Th e bro-ken line is the extrapolation of the BR trend to 2005.

Figure 1 shows that BR achieved a long-term reduction in the movement and non-movement accident rate, estimated at –3.6% per year, though the data are somewhat more scat-tered about the trend than would be expected of a Poisson variate. Th e right-hand side of the fi gure shows that, if we take the extrapolation

of BR’s favourable trend as an estimate of the numbers of fatal accidents to be expected if BR had continued, the privatised railway has bet-tered that trend in every subsequent year. If we test for a change in accident rate by introducing a step change in the accident rate at the date of privatisation, the estimated step is downwards, and is signifi cantly diff erent from zero. It does not necessarily follow that privatisation actu-ally caused an improvement in safety, because the improvement could have other causes, but it is powerful evidence against the opposite hy-pothesis that privatisation worsened safety.

Table 2 compares the actual number of fatal accidents in 1994–2005 with the number that would have been expected on BR’s trends. Th e table also shows the corresponding num-bers of fatalities. Minus signs in the bottom row indicate that the performance of the post-privatisation railway was better than expected. Plus signs indicate that it was worse.

Fatal train collisions, derailments and overruns

If fatal movement and non-movement accidents did not become worse, what about train colli-sions, derailments and overruns? Because the numbers of these accidents are small, the annu-al data are scattered, and the data are easier to comprehend if they are combined into longer periods. Figure 2 plots the number of accidents in (mostly) 5-year periods. Table 3 shows the data on both accidents and fatalities.

Figure 2 shows a similar pattern to that of movement and non-movement accidents. BR

Table 1. Fatal accidents and fatalities: main line railways, 1967–2005

Number of accidents Number of fatalities

Movement and non-movement accidents 2007 2070

Train accidentsTrain collisions, derailments, overruns 80 320Train–road vehicle collisions 176 249Other train accidents 32 48

All fatal accidents 2295 2687

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1965 1970 1975 1980 1985 1990 1995 2000 2005Year

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trai

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Figure 1. Fatal movement and non-movement accidents per million train-kilometres, 1967–2005

17march2007

achieved a signifi cant downward trend in the train accident rate in 1967–1993, estimated to be –5.0% per year. If this trend is extrapolated, the number of accidents that actually occurred in 1994–1998 is about on the trend, and the number in 1999–2005 is below trend. Th ere-fore, the number of train accidents was some-what smaller than would be expected from ex-trapolating BR’s favourable trend, as shown in Table 2. In this case the reduction in accidents

from 1994 is not signifi cant, but again it is evi-dence against the hypothesis that the accident rate increased, notwithstanding the four high profi le accidents in 1997–2002.

However, the plus sign in the bottom line of Table 2 shows that, although the number of post-privatisation train accidents was smaller than expected, the number of fatalities was greater. Furthermore, the right-hand column of Table 3 shows that the average number of

fatalities per accident was 6.6 in 1994–2005, compared with 3.7 in 1967–1993. However, because of the high variability in the numbers of fatalities in individual accidents, and the small number of accidents in 1994–2005, the two means are not signifi cantly diff erent. More spe-cifi cally, the high mean in 1994–2005 is largely because of the high number of fatalities in the Ladbroke Grove accident in a period when train accidents generally had become infrequent. It would not be reasonable to infer that privatisa-tion had caused accidents to become systemati-cally more severe, not only because the increase is not signifi cant, but also because privatisation could be expected to aff ect accident frequencies rather than accident consequences.

Collisions between trains and road vehicles

Th e third type of accident included in Tables 1 and 2 is collisions between trains and road vehicles. BR achieved reductions in these ac-cidents, but at a relatively slow rate. Table 2 shows that the privatised railway again bet-tered the extrapolation of BR’s performance, both in accidents and fatalities.

Conclusion from accident data

BR achieved downward trends in the accident rates from 1967 to 1993 for all the main class-es of fatal accident. Nonetheless, these trends were bettered in 1994–2004 for all classes of

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1965 1970 1975 1980 1985 1990 1995 2000 2005Year

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1967-1971

1972-1976

1977-1981

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1994-1998

1999-2005

Figure 2. Fatal train collisions, derailments and overruns per billion train-kilometres, 1967–2005

Table 2. Actual and expected accidents and fatalities: Great Britain, 1994–2005

Fatal movement and non-movement accidents

Fatal train collisions, derailments and overruns

Fatal train/road motor vehicle collisions

Accidents Fatalities Accidents Fatalities Accidents FatalitiesActual 259 267 9 59 35 55Expected from BR trends 407 420 12.5 46.1 52.3 71.9Actual – expected −148 −153 −3.5 +12.9 −17.3 −16.9

Table 3. Fatal train collisions, derailments and overruns: 1967–2005

Period Years Train-km (billions) Accidents Accidents per billion train-km

Fatalities Fatalities per accident

1967–1971 5 2.25 25 11.1 109 4.41972–1976 5 2.18 14 6.4 39 2.81977–1981 5 2.13 10 4.7 27 2.71982–1986 5 1.99 11 5.5 28 2.51987–1993 7 3.00 11 3.7 58 5.31967–1993 27 11.55 71 6.1 261 3.7

1994–1998 5 2.22 6 2.7 17 2.81999–2005 7 3.61 3 0.8 42 14.01994–2005 12 5.83 9 1.5 59 6.6

18 march2007

accident. Only one indicator is adverse: the number of fatalities in train collisions and de-railments is higher than expected because of the severity of the accident at Ladbroke Grove in 1999. However, it is not reasonable to con-clude that accidents tended to be more severe after privatisation. Th e conclusion from the analysis of the accident data is that there is no evidence for the hypothesis that railway safety, as measured by accidents, has become worse since privatisation.

Why is it believed that safety became worse?

Nevertheless, it is widely believed than safety did get worse. Why is it? Th e principal argu-ment is based on detailed accounts of specifi c accidents, particularly the four high-profi le train accidents in 1997–2002. For each acci-dent, the question is asked “Would this acci-dent have happened under BR?” In most cases, the answer off ered is “no”, and the inference is then made that, therefore, there would have been fewer fatal train accidents without priva-tisation. Wolmar1 makes a persuasive case for this argument.

Th e arguments that specifi c accidents would not have happened under BR are, by their nature, not provable, but they are plausi-ble for at least some of these accidents. How-ever, to accept that specifi c accidents would not have happened in other circumstances is not to accept very much, because most accidents would not have happened in diff erent circum-stances. Most accidents are the outcome of a chain of events involving several people, and diff erent actions by any one of a number of people would normally have been enough to prevent them. People’s actions are conditioned by the organisations in which they work, and therefore it is certainly possible that changing the organisational structure (such as privatis-ing the railways) aff ects the occurrence of ac-cidents.

However, this argument works in both directions. It is possible that the change in the organisational structure associated with pri-vatisation has had positive as well as negative eff ects. Th us, it is possible that the change has led people to take actions that prevented ac-cidents that otherwise would have occurred. Furthermore, if that were so, we would not know about them from accounts of specifi c accidents, because prevented accidents are non-events, and not recorded. Not even those who had prevented accidents would necessar-ily know that they had done so. Th erefore, ac-counts of specifi c accidents are biased in the

direction of leading to the conclusion that changes are for the worse: we know about the accidents that occur, but we do not necessarily know about the accidents that are prevented.

Another reason why it is believed that safety has become worse since privatisation is what Newman2 labels “the power of stories over statistics”. Most of us comprehend stories more easily than statistics, and accounts of railway accidents make exceptionally compelling and tragic stories. Newman notes that accounts of accidents are particularly persuasive when they come from those who were directly involved. Th ese include, not only the bereaved and in-jured, but also others such as staff and rescue workers. Th e stories are given added power by the fact that they sometimes do indeed dem-onstrate mistakes or incompetence by railway organisations.

Th e ease with which the high profi le ac-cidents are recalled, and the frequency with which they are publicly revisited, lead people to overestimate their probabilities. Th e origi-nal accounts of the major accidents remain in people’s minds, and these are amplifi ed by the fact that the accidents may be the subject of inquiries and legal proceedings stretching over

several years. On each occasion, the story of the accident is recounted, and it then seems almost as if another accident has occurred.

Th e fatal train accidents have also pro-vided a focus for more general dissatisfaction about railway privatisation. Th ey are the public events that have come to encapsulate a wider range of concerns than safety, and in doing so have made the safety performance seem worse than it is.

Th is article is based on Evans (2006)3, where more information can be found.

References1. Wolmar, C. (2005) On the Wrong Line:

how ideology and incompetence wrecked Britain’s rail-ways. London: Aurum Press.

2. Newman, T. B. (2003) Th e power of sto-ries over statistics. British Medical Journal, 327, 1424–1427.

3. Evans, A. W. (2006) Rail safety and rail privatisation in Britain. Accident Analysis and Pre-vention, doi: 10.1016/j.aap.2006.09.007 (in press)

Andrew Evans is Lloyds Register Professor of Risk Management at Imperial College. He is also Chairman of the Rail Safety Working Groups of the Parliamentary Advisory Council on Transport Safety.