But this dores not mean that other costs should be ignored. The concept of generalised cost can be extended further to include other elements such as comfort, convenience, reliability, safety, etc. It is quite common to include the value of accidents within the cost benefit format as part of the quantified total generalised cost. It is less common to include the other elements in monetary form. Reductions in travel time variability, associated particularly with the reduction of congestion, may in practice be valued even more highly than reductions in the average or expected travel time.
Generalized cost is important both in forecasting and evaluation.
For example, at the forecasting stage, an assumption that users are simply aiming to minimize their money costs, when in fact they attach great significance to time saving, may lead to serious errors in forecasting changes in traffic levels associated with transport improvements. By the same token, however, if individual consumer decisions are heavily determined by elements of the total cost other than monetary outlay, it is illogical to treat those elements as of no value in the social evaluation process as they plainly affect individual welfare. It should therefore be the rule, rather than the exception, that all elements considered in determining consumers choices should be included in the evaluation of projects at prices calibrated on the behaviour of individuals concerned in making the choices.