The key variables of financial viability for any major project are costs (investment, financing, operations and maintenance) and revenues (mainly tolls in the case of transport projects). For each variable, forecast values may be different from actual values as documented above. Ar isk therefore exists that actual project viability may be substantially different from forecast viability.

The difference between forecast and actual viability may be so large that if the actual viability had been known for a given project, decision makers might have resolved:

1. (i) not to implement the project;

2. (ii) to implement the project in another form; or

3. (iii) implement another project.

In other words, non-viable projects, or projects that are less viable than forgone projects, may be implemented not because they are viable but because their viability was inaccurately predicted. The result would clearly be an inefficient use of resources.

Channel tunnel, Great Belt and Øresund

For the Channel tunnel, original estimates of viability have been rendered irrelevant by actual developments which have taken the project on a rollercoaster ride from expected high profitability to several near-bankruptcies. Most observers today consider the commercial viability of the Channel tunnel unproved and the prospect uncertain for original investors making a satisfactory profit.

After being issued at £3.50 per share on 9 December 1987, by mid-1989 initial optimism had spiralled Eurotunnel share prices to more than three times this value, above £11.00. Then delays and cost overruns hit the project, resulting in capital shortage and crisis.