The Green Book identifies six specific classifications of project type, each with different Optimism Bias uplift factors. These are: standard buildings; non-standard buildings; standard civil engineering; non-standard civil engineering; equipment/development; and outsourcing.
Careful consideration must be given to the characteristics of a project when determining its project type. The majority of transport projects will be classified as either standard or non-standard civil engineering projects. For example, the building of new roads and the up-grading of existing roads will usually be classified as standard civil engineering. Meanwhile, more unique projects such as building a tunnel for a railway would be classified as non-standard civil engineering. Comparing these two types of projects, the evidence suggests that the Optimism Bias for non-standard civil engineering tends to be higher than for standard civil engineering. For further information on the upper and lower bounds of Optimism Bias for the different classifications of projects, reference should be made to Mott MacDonald's report on large-scale public procurement in the UK.
Table 13.2 illustrates the typical project categories specifically for transport appraisal, derived from the Bent Flyvberg (2004) work.
Table 13.2: Project Categories
|
Category |
Types of Project |
| Roads | Motorway Trunk roads Local roads Bicycle facilities Pedestrian facilities Park and Ride Bus lane schemes Guided buses on wheels |
| Rail | Metro Light rail Guided buses on tracks Conventional rail High speed rail |
| Fixed Links | Bridges and tunnels |
| Building Projects | Stations and terminal buildings |
| IT Projects | IT system development |
Source: Flyvbjerg (2004)
For ferry schemes, it should be noted that the cost of purchasing ferries is not considered an infrastructure investment, and therefore is not subject to Optimism Bias. Practitioners may wish, however, to perform sensitivity tests to their cost estimates. The costs of building ferry infrastructure such as slipways should be subject to the standard building projects Optimism Bias levels.
