Economic versus financial analysis: differences and interaction 
A confusion is often observed between economic analysis and financial analysis. Although the definitions may vary and some concepts attached to each of the two topics be not so easy to tackle, a rough distinction can be established:

The financial analysis consists in comparing revenue and expenses (investment, maintenance and operation costs) recorded by the concerned economic agents in each project alternative (if relevant) and in working out the corresponding financial return ratios ;

The economic analysis aims at identifying and comparing economic and social benefits accruing to the economy as a whole, setting aside for example monetary transfers between economic agents.

This may give rise to some confusion may arise: although tolls do not directly take part in the economic computation of total benefits (except in the case of generated traffic, but this would require further explanation) they are nevertheless a key factor of the economic analysis because the level of tolls will affect the transport demand and thus the economic ratios of the project, and in particular the economic rate of return (depending on the gap between the economic optimum and the actual pattern). 

There is in fact a double trade-off when trying to set up a toll rate:
the economic optimum does not necessarily correspond to the financially preferable solution (see development of this point in Influence of tolling on transport demand; - it must be remembered that without congestion, the economic optimum toll rate is zero!
the toll level balancing economic and financial constraints may not correspond to the willingness-to-pay of the road users. 

Finally, it must be remembered that economic and financial analyses are not self-contained topics: they are used to verify the economic and financial sustainability of the projects likely to be implemented. 

Going back to the examples quoted above, the financial sustainability of a given project may not be compatible with the economic sustainability, and the value of key parameters like tolls must be adjusted in order to cope with both economic and financial constraints (see also willingness to pay).