Measuring affordability
In considering whether or not to grant a fare increase application, many authorities take into consideration a measure of affordability. There is unfortunately no internationally agreed method of measuring affordability when applied to bus services.

However the normal approach is to divide the price of a number of standard journeys by some measure of income. While conceptually this is a simple measure, it is not easy to measure either parameter. The cost of a journey can vary significantly depending on the distance travelled and whether monthly passes are used or not. Equally, income is also difficult to measure on a standard basis.

Unless there is reason to select a specific journey, it is probably best to take the average fare paid by all passengers as the measure of the fare, and either the average income of all groups or the GDP per capita if available. The figures are usually compared on a monthly basis, and therefore the cost of a standard number of trips, e.g. 50 per month, is usually compared with the average monthly wage.

This measure is most useful when used to compare a fare/income ratio in a particular city over a period of time as incomes change.

Average fare paid per boarding
This indicator may be used in conjunction with information on income levels to assess the affordability of bus fares.

Unless there is a flat fare structure, it is also useful as a guide to the average distance travelled by passengers. The lower the average fare, the shorter the average distance travelled; a very low average fare may also indicate that there is a problem of pilferage or fare evasion, principally through over-riding, which should be investigated.

The average will be influenced by average distance travelled, and also by the number of passengers in different fare categories, such as students and other passengers paying fares at concessionary rates.

Average monthly wage
The average monthly wage for the population of the area served by the bus system is useful in determining affordability of bus fares. This information is not always available. In some countries the figure is calculated for the country as a whole; but urban incomes are usually significantly higher than average incomes for the country as a whole.

Percentage of monthly wage for 50 average boardings
This is a measure of affordability. A typical urban bus user will make approximately 50 boardings per month. The lower this percentage, the more affordable the bus fare.