Prediction, appraisal and evaluation of road pricing schemes

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Prediction, appraisal and evaluation of road
pricing schemes
What can we learn about Prediction, Appraisal and
Evaluation?

• Professor Anthony D May
• Institute for Transport Studies
• University of Leeds

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The State of the Art Report

• First version now approved by the Commission and
  published
• A web-based version proposed
• Four sets of reviews by international experts
• Australia, Hong Kong Korea, Singapore, US
• Second version in draft for completion in January
• Updates to all chapters
• Reflecting comments received and new results
• New chapters on Technology, Environment
• What focus for Technology? Should we add Business
  Models?
• Fact sheets being prepared for each chapter
• Two drafts available for Acceptability, Economy
• Comments welcome!

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The SoAR structure
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Prediction

• Prediction enables us to assess what the likely
  impacts of a proposed scheme might be
• And is hence the key input to Appraisal
• Methods of formal prediction are essential
  because
• It is very difficult without them to assess the
  complex impacts of road pricing
• There is very little empirical evidence on which
  to base simpler assessments
• But the lack of empirical evidence makes it
  harder to establish reliable prediction methods
• Prediction was ranked second in the Use Needs
  Assessment Questionnaire

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What do we need to predict?

• The direct impacts of different designs on demand
  and supply
• The demand effects on different types of user,
  including those exempt or charged at different
  levels
• Changes in mode, route, time of travel,
  frequency, destination . . .
• The supply effects on different parts of the
  network
• Private and public transport networks
• Capacity, flows, travel times, waiting times,
  queues, reliability . . .
• The impacts on different objectives
• Including distributional effects
• The short and long run impacts

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Types of predictive model

• Micro-simulation models (e.g. VISSIM, DRACULA)
• Detailed interaction of vehicles, principally for
  detailed impacts
• Tactical network models (e.g. SATURN)
• Re-routeing impacts of charging, and simple
  demand responses
• Strategic transport models (e.g. EMME2, TRIPS)
• Broad demand responses, high level network
  impacts
• Strategic land use/transport models (e.g. MEPLAN,
  MARS)
• High level demand responses, relocation impacts
• General equilibrium models (e.g. TRENEN)
• High level economic impacts

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Gaps in our ability to predict

• Area-based schemes
• Exemptions, discounts and season tickets
• Trip chaining, motorcycles, vehicle occupancy
• Park and ride, park and walk
• Waiting times and reliability
• Distributional impacts, particularly for
  exclusion issues
• Longer term impacts on location and economic
  activity
• Hence impacts on certain objectives
• Equity, Economy
• Which might bias the design and assessment

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Appraisal and Evaluation

• Appraisal involves ex ante assessment of the
  predicted impacts
• And helps guide the decision on whether to
  implement
• And how to improve the design
• Evaluation involves ex post assessment of the
  measured outcomes
• And is essential for improving our ability to
  predict and appraise
• And for increasing acceptability, enhancing
  transferability
• Both should be based on the full list of agreed
  objectives
• Ideally evaluation should also consider
  objectives of interest to other cities

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Appraisal methods

• Conventional approaches
• Cost Benefit Analysis and Multi-Criteria
  Appraisal
• CBA provides a simple aggregate assessment
• But misses distributional impacts and those
  difficult to value
• MCA provides a disaggregate assessment by
  objective
• But can involve questionable weighting procedures
• And may still not address distributional impacts
  well
• Useful guidance in HEATCO very detailed,
  prescriptive guidance in UK WEBTAG
• Several examples of more or less good practice

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Evaluation examples

• London and Stockholm have both provided very
  detailed information on what has happened, and
  what impacts this has had on objectives
• London has now provided over three years of
  time-series data
• Which shows the impact of changes in
  specification
• And raises the question of whether the impacts
  are being eroded
• But even London has had difficulty with
  evaluating some impacts
• And both have been subject to re-interpretation

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What have we learned from London?

• Congestion is difficult to measure, and
  influenced by other factors
• Reductions in road space road works
• Reliability also difficult to measure and
  different for private, public transport
• Benefits sensitive to values of time assumed
• Safety benefits are more easily measured than
  predicted, but are we sure about cause and
  effect?
• Economic impacts are even more difficult given
  the wide range of other factors which affect
  performance
• Distributional impacts depend on identifying the
  right impact groups and being able to measure the
  impact on each of them
• Charge payers compliance is difficult to
  predict, but important for performance

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Two evaluations of Stockholm
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Critical differences

• P/K attribute the costs of additional suburban
  buses to the congestion charging scheme. Is this
  right? Are there no benefits to existing PT
  users?
• E calculates additional rail capacity costs of
  63m SEK/yr plus 15m SEK/yr in overcrowding costs.
  P/K calculate a fragile estimate of
  overcrowding costs of 222m SEK/yr. But is it
  right to apply the changes in standing to the
  whole of the traffic for the whole of their
  in-vehicle time?
• These differences account for 1383m SEK out of
  1451m SEK (95) of the difference between P/K and
  E

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Gaps in our ability to appraise

• Overcrowding and unreliability
• Qualitative environmental impacts such as
  streetscape
• Distributional impacts impact groups and
  measurement
• Economic and other long term impacts
• Interactions with administration and enforcement
• Treatment of uses of revenue
• Scope of the appraisal or evaluation
• The scheme itself
• The scheme together with complementary policies
• The scheme together with uses of its revenue