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Presented by Name HereJob Title - Date
Monitoring national casualty trends in Great BritainJeremy Broughton16 November 2009
Page 2
Contents
Background
Casualty forecasts for 2010
GB Casualties in 2008
1
2
3
4
5
Monitoring casualty trends
Car Secondary Safety
Background
Page 3
In the late-1990s the British Government began to prepare for the next road accident casualty reduction target, the target year would be 2010
The context for the target was provided by forecasts of the number of casualties in 2010- The forecasts needed to take account of the effects of national policy
where it could be established reliably
- They should also take account of the changing volume of road travel
The presentation will describe how the forecasts were prepared
Progress towards the target has been monitored annually, which has allowed the reliability of the forecasts to be checked
The implications of the 2008 data for the forecasting procedure will be examined.
Approach to casualty forecasting
Page 4
The approach is based on analyses of past casualty rates per billion veh-km of traffic
Previous research (in GB and other countries) had found that national casualty rates declined exponentially
This model had provided useful forecasts, but needed to be improved to take account of road safety policy
4.0
4.5
5.0
5.5
6.0
1978 1983 1988 1993 1998
ln(K
SI p
er b
illio
n ve
h-km
)
Casualty forecasts
Page 5
Most road safety measures affect different groups differently so the forecasts are disaggregate, with five road user groups:- car occupants
- motorcyclists
- pedestrians
- pedal cyclists
- others (mainly people travelling by bus, coach, van or lorry)
The casualty rates are adjusted to take account of the DESS measures:
- Reducing Drink/Driving
- Road safety Engineering
- Improved Secondary Safety (crashworthiness) of cars
The adjusted rates estimate what would have happened without the DESS measures.
Idealised illustration of the forecasting model
Page 6
1988198919901991199219931994199519961997199819992000200120022003
1980 1985 1990 1995 2000 2005 2010 2015
casualty rate (arbitrary scale)
Adjusted rate, 1983-98, showing what might have happened without the DESS measures
A What might happen in 1999-2010 with the Core program but no further DESS measures
B
Fi
Assumed effect of new policies
Actual rate
Baseline forecast
Final forecast
An actual forecast
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This example is for car occupants KSI (Killed or Seriously Injured)- The red line is fitted to the
adjusted rates from 1983 to 1998
- This is extrapolated to 2010 to forecast the rate
- The forecast rate is multiplied by the volume of car traffic forecast for 2010 to estimate the number of casualties
- The traffic volume comes from a ‘transport scenario’
3.9
4.2
4.5
4.8
1983 1988 1993 1998 2003 2008
log
(KS
I rat
e)
The outcome
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The actual rates have been added to the previous slide for car occupants KSI- The outcome matched the
forecast for the first four years
- From 2003 the rate has fallen below the forecast, indicating that new policies have taken effect
- These falls are independent of the benefits of improved secondary safety of modern cars (considered later)
Different patterns are found with the other road user groups
3.9
4.2
4.5
4.8
1983 1988 1993 1998 2003
log
(KS
I rat
e)
Transport scenarios
Page 9
There is uncertainty about traffic growth, so a range of ‘transport scenarios’ was defined, based on official (DfT) forecasts for 2010
Each scenario consisted of a growth prediction for each of the 5 road user groups
Implausible combinations were excluded (e.g. car use and walking would both grow strongly)
This left 36 scenarios, and a set of forecasts (KSI, slight casualties) was prepared for each
New measures
Page 10
These include innovatory measures that might be taken, also substantial expansion of existing measures
The ‘Safety Targets and Accident Reduction’ Group was set up to consider the new measures that might be included in the future road safety strategy
The outcome was a list of 9 possible new measures, and the potential effectiveness of each was assessed using available evidence
The casualty forecasts depend upon which of these measures are assumed to be implemented
A review in 2007 concluded that by 2010 about 75% of the predicted benefit would have been achieved
Final forecasts for 2010
Page 11
KSI and slight casualty forecasts were prepared for each of the 36 transport scenarios
Each pair of forecasts is plotted as a point on this figure (100%=no change from 1994-98 baseline)
Attention focussed on the more plausible scenarios
Fatality forecasting
Page 12
Trends for Killed and KSI had been very similar until 1998, so no specific target was adopted for Killed
The trends have since diverged, so attention has focused on forecasting fatalities
The same approach had proved successful60
80
100
120
140
1990 1995 2000 2005
10
0=
19
94
-98
ave
rag
e
Killed KSI
Fatality forecasting: 2007 and 2008 data
Page 13
The number Killed fell by 7% in 2007 and by 14% in 2008
These sudden changes call into question the approach to casualty forecasting
Some preliminary results will be presented
60
80
100
120
140
1990 1995 2000 2005
10
0=
19
94
-98
ave
rag
e
Killed KSI
The casualty trends for pedestrians did not change
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There is no sign of a trend change for pedestrians in 2007 or 2008, so the pedestrian casualty forecasts are not affected.
The same is true of pedal cyclists and of motor-cyclists.
2.2
2.7
3.2
3.7
4.2
0.2
0.7
1.2
1.7
2.2
1983 1987 1991 1995 1999 2003 2007
Log(
seri
ous r
ate)
Lo
g(f
ata
lity r
ate
)
Pedestrians
Killed Serious
…but the fatality trend for car occupants did
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The trend for serious car occupant casualties was unchanged in 2008, so the forecast is not affected
The trend for fatal car occupant casualties fell sharply in 2008, following the precedent of the previous recession in 1990
The same is true of "Others”, the great majority of whom travel by bus, coach, van or lorry.
Why are the responses of the fatal and serious trends different?
3.0
3.5
4.0
4.5
5.0
1.5
2.0
2.5
3.0
3.5
1983 1987 1991 1995 1999 2003 2007
Log(
seri
ous r
ate)
Log
(fat
alit
y ra
te)
Car occupants
Killed Serious
Improved Secondary Safety of cars
Page 16
Secondary safety (crashworthiness) refers to the protection offered by a vehicle involved in an accident, whereas primary safety refers to systems such as steering and brakes which should help to avoid accidents.
Changes in secondary safety can be assessed by studying the proportion of injured car drivers who are Killed or Seriously Injured
Cars are grouped by their ‘year of first registration’. In any one year of accidents, drivers of newer cars tend to be less seriously injured
A statistical model is used to identify the effect
Some results
Page 17
Separate analyses are made for Killed and seriously Injured on Built-Up (urban) and Non Built-Up (rural) roads
In each case, results show that secondary safety began to improve about the 1990 model year, and progress since then has been steady
Future benefits can be estimated, conditional upon an assumption about how much longer this progress will continue
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
pre-1976 1980-81 1986-87 1992-93 1998-99 2004-05
log
(re
lativ
e s
eve
rity
pro
po
rtio
n)
Killed, NBU
model_1
model_2
Summary results
Page 18
These detailed results can be summarised by comparing cars first registered in 2006-07 with those first registered in 1990-91
About 2/3 fewer injured drivers of the more modern cars were killed , and about 2/5 fewer were seriously injured
A problem for the future: how to assess the benefits of advanced primary safety features such as Electronic Stability Control?
Reduction in the proportion of casualties who were killed or
seriously injured
KilledSeriously injured
Urban roads 67% 42%Rural roads 59% 43%
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Thank you
Presented by Jeremy Broughton16 November 2009Tel: 01344 770879
Email: [email protected]