The Accidents Sub-Objective
TAG Unit 3.4.1
June 2005 |
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 Unit
3.4.1 |
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1 The Accidents
Sub-Objective
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1.1 Introduction
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 1.1.1 |
There are methodological differences in the
way that accidents are appraised for road schemes and other
modes. The approach described below should be used for appraising
changes in the number of road accidents. Where proposals are
expected to have a significant impact on railway accidents,
these should be noted. Further advice on how these impacts
should be appraised should be sought from the SRA, see Appraisal
Criteria (SRA, April 2003)
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| 1.1.2 |
Transport accidents impose a range of impacts
on people and organisations, including: |
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- medical and healthcare costs*;
- lost economic output*;
- pain, grief and suffering*;
- material damage†;
- police and fire service costs†;
- insurance administration; and
- legal and court costs†.
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| 1.1.3 |
Those impacts marked (†) are closely
related to the number of accidents, while those marked (*)
are related to the number of casualties. Therefore, numbers
of accidents and numbers of casualties are the key quantitative
indicators for the assessment of proposals. Combining these
numbers with values for the prevention of casualties and accidents
provides a monetary estimate of the accident benefits of proposals.
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| 1.1.4 |
The impact of casualties
differs according to the severity of the injuries sustained.
Three groups are usually differentiated; these are defined in
the following way: |
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- fatality = death within 30 days from causes arising out
of the accident;
- serious injury = casualties who require hospital treatment
and have lasting injuries, but who do not die within the
recording period for a fatality; and
- slight injury = casualties whose injuries do not require
hospital treatment, or, if they do, the effects of the injuries
quickly subside.
More detailed information on classification of particular
types of injury can be found in Hopkin and Simpson,
1995.
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| 1.1.5 |
Values for the prevention of a casualty should
be those currently used for road appraisal, contained in the
latest DfT advice (DMRB Volume 13, Section 1 and Highways
Economics Note 1, 1999f).
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| 1.1.6 |
The impact of accidents
varies also according to severity. For road accidents, the
accident-related costs to be used should again be those specified
in the latest DfT advice (DMRB Volume 13, Section
1, 1996 and HEN1, 1999f).
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| 1.1.7 |
Standard processes exist for forecasting
the numbers of accidents and casualties and the accident reduction
benefits arising from changes to the road network.
For most major proposals, forecasts should be generated using
the methods and accident rates contained in the COBA Manual
(DMRB Volume 13, Section 1) and embodied in the computer program
COBA. The techniques used to measure the change in the number
of accidents (with differing degrees of severity) are based
on established parameters for the number of accidents per
million vehicle-kms on different types of road. As the number
of vehicle-kms on the network change as a result of the introduction
of an intervention, so the number of accidents will also alter.
Thus, if the impact of an intervention is to reduce the number
of vehicle-kms travelled, then this will tend to reduce the
number of accidents on the network. Similarly, if the intervention
causes a reduction in the number of vehicle-kms on one type
of road but an increase for a second type of road, then the
net impact on the number of accidents will depend upon the
relative accident rates for the two types of road.
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| 1.1.8 |
Application of the guidance set out above will
provide estimates of the change in the numbers of road user
accidents and of the monetised present value of accident reduction
benefits. These values should be reported in the AST, for
all options, whether they include road or public transport
components or combinations of the two. This will ensure consistent
comparison of impacts between options.
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| 1.1.9 |
However, when assessing the likelihood that
public transport options will qualify for subsidy or grant,
accident reduction benefits will need to be adjusted to comply
with the different assumptions specified in the appropriate
guidelines. For further guidance, see Detailed Guidance
on Major Scheme Appraisal in Local Transport Plans (Tag
Unit 3.9). Analysts should ensure that their assessment
of accident reduction benefits are sufficiently disaggregate
to enable these adjustments to be made.
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2 Application
of TAG to Highway Schemes
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This section provides advice on the links between
TAG's treatment of the accidents sub-objective and the advice
given in Volume 11 of the Design Manual for Roads and
Bridges (DMRB), which deals with the environmental assessment
of highway projects. An explanation of the correspondence
between the advice set out in TAG and DMRB is given in Applying
the multi-modal new approach to appraisal to highway schemes
(TAG
Unit 2.6).
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2.1 Methods
and Worksheets
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| 2.1.1 |
The methodology for accident calculations is given
in the COBA manual (DMRB Vol 13, Section 1, 1996). However,
the parameters used in calculations in the Volume 13 are superseded
by those given in the Interim COBA11 Guidance. Changes have
been made to: |
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- Accident rates, severity splits and costs have been revised
in accordance with latest data;
- Unit values. These are now expressed in 2002 market prices; and
- Accident rates and severity splits now change over time,
in order to be consistent with observed trends and likely
policy developments.
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| 2.1.2 |
The quantitative entry is the change in number of total personal injury accidents, and casualties by severity, over the 60 year period. The Present Value of Benefits for accidents should be expressed in 2002 market prices, discounted to 2002.
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| 2.1.3 |
TUBA does not include calculation of the PVB
of accident savings. The COBA11 program should be used to
calculate the PVB of accidents for traffic forecasts using
both fixed and variable trip matrices.
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| 2.1.4 |
COBA can be used to assess the safety impacts of both fixed and variable trip matrix appraisals. |
| 2.1.5 |
QUADRO may be used to perform calculations for accidents during construction and accidents during maintenance. An updated version of the program will be available in Spring 2001.
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3 References
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Department of the Environment, Transport and
the Regions (DETR), Design Manual for Roads and Bridges:
Volume 13 Economic Assessment of Road Schemes, The Stationery
Office: London.
Department of the Environment, Transport and the Regions
(DETR) (1999), Highways Economics Note 1 (HEN 1),
DETR: London.
Hopkin, J M and Simpson H F (1995) Valuation of Road
Accidents, TRL Report 163, Transport Research Laboratory,
Crowthorne.
DETR Mobility Unit (1998b), Secure Stations Scheme,
DETR: London.
SRA (April 2003) Appraisal Criteria |
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4 Document
Provenance
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This Transport Analysis Guidance
(TAG) Unit is based on Chapter 5, Section 2 of Guidance
on the Methodology for Multi-Modal Studies Volume 2 (DETR,
2000).
Technical queries and comments on this TAG Unit should be
referred to:
Integrated Transport Economics and Appraisal (ITEA) Division
Department for Transport
Zone 3/08 Great Minster House
76 Marsham Street
London
SW1P 4DR
itea@dft.gsi.gov.uk
Tel 020 7944 6176
Fax 020 7944 2198 |
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