Urban Road User Charging Online Knowledge Base
What Is The Importance Of The Theme?
What do we mean by appraisal?
Appraisal is the process of assessing, in advance of implementing a policy such as a road pricing scheme, whether it will be effective in meeting the city’s objectives and, where appropriate, whether it will satisfactorily avoid any constraints which the city places on the scheme. Appraisal should be based on the full list of objectives of the road pricing scheme, as discussed in Chapter 2.
At its simplest, it can be applied to one proposal, and used to answer the simple, but often challenging question: should we implement this scheme? However, with as major a change as the implementation of road pricing, it is common to develop a number of policy options and compare them to produce a shortlist of possible schemes. As an example, the London Congestion Charging study of the 1990s considered over 40 possible design options, and appraised them against a common set of objectives (May et al, 1996). Less commonly, but equally importantly, appraisal can be used at an early stage in the development of options to identify weaknesses in them which can be overcome. For example, if a given design is effective in reducing congestion, but adversely affects a particular group of users, they could be provided with an exemption.
Thus appraisal can be used to answer three types of question:
• Does this design option have weaknesses which could potentially be improved?
• Which of these design options performs best against our objectives?
• Should we implement the best design option?
How important is appraisal to decision makers?
Appraisal, considered independently in the UNAQ results, was only ranked 5 out of the 9 themes. It is difficult to determine why this was. It may be that most cities answering the questionnaire were at too early stage in considering design options to have given much thought to appraisal. However, prediction was ranked second and, as noted below, it is difficult to enter into the process of prediction without considering the types of answers which are needed, as input to the appraisal process. It may be that respondents were implicitly grouping prediction and appraisal together in their responses. In practice, the importance of appraisal to decision-makers cannot be overestimated, as the outcomes are critical to decisions about whether to implement a given scheme and are often the primary basis for choosing between alternative options.
What should we appraise?
The answer to this question may seem obvious: we should be appraising the set of options for road pricing. But it is important to define carefully the boundaries of what is appraised. As noted in Chapter 3, a scheme can be the road pricing cordon or area itself, with the set of charges, discounts and exemptions applied. Even at this level, the appraisal should extend to consider the performance of the technology (Chapter 4) and the administrative and enforcement processes (Chapter 5).
But one of the principal purposes of a road pricing scheme may well be to generate revenue. If this is the case, should the appraisal simply assess the level of revenue generation, and the possible benefits of having access to that revenue? Or should the package be the road pricing scheme and the enhancements which that revenue has financed?
Looked at another way, road pricing will typically only be successful if it is implemented as part of a package of measures, which will include public transport improvements, and will probably also include traffic management measures to facilitate diversion and to enhance environmental benefits. Had the road pricing scheme been implemented (or designed) without these complementary measures, it would have performed differently. Thus there is a strong case for specifying the boundaries to include the full package of measures and appraising or evaluating that package. This makes the scale of the appraisal task greater, but it will substantially improve the understanding of what might happen.
How does appraisal relate to the objectives of road pricing?
As noted above, appraisal should assess whether a scheme will meet the city’s objectives, and evaluation should assess whether it has met them. As noted in Chapter 3 it is essential that cities enter the process of road pricing scheme design with a clear understanding of their objectives, and of the relative importance of them. In some cases, less direct objectives can be expressed as constraints; for example: “to reduce congestion and enhance the environment, subject to not adversely affecting the economy”. These same objectives and constraints should be used in the appraisal and evaluation processes. Some appraisal procedures permit the objectives to be weighted to express their relative importance (see Section 11.3).
How does appraisal relate to prediction?
For most of the objectives listed in Chapter 2, it will not be self evident how a particular scheme would perform. Instead it will be necessary to carry out a formal process of prediction to estimate how travel patterns might change, and what impacts these would have on outcomes such as congestion, accidents, air pollution and the economy, as discussed in Chapter 6. Thus the prediction process informs the appraisal, and should be designed to provide the information which the appraisal process requires. In practice, therefore, it is better to specify the appraisal process first before finalising the prediction methods.
As noted in Chapter 6, outcomes for some objectives, such as impacts on the urban economy, will be harder to predict than others. There is thus a danger that they will be overlooked. An effective appraisal process should be aware of these weaknesses in prediction, and take steps to allow for uncertainty in such impacts.
As mentioned in Chapter 15, a comparison between appraisal and evaluation can indicate how well the prediction process has worked and this knowledge can be used to enhance the prediction process.
No information on this theme is currently available from the case studies