Students of evaluation have classically identified two major different kinds: pre-(or prior) and post-evaluation. Prior evaluation is inevitably associated with decision making — where we are faced with a choice between options, which option is preferable? The development and application of appropriate methods to assist with this task has a long history in land-use and transport planning. The transport field is characterized as one involving substantial public expenditure, which then provides a mixture of benefits and, indeed, disbenefits. A major factor necessitating a rethink of transport policy was the impact of increasing congestion on European cities, caused largely by the steady increase, in daily private car commuters. The possible transport alternatives were to be considered against two objectives: To provide relief from the anticipated effects of increasing traffic on the M4 Motorway around Newport; and To appraise options on the basis of acceptable environmental, financial, economic and safety criteria.