The emission performance of the buses has improved a lot the last 20 years. The gradual decrease of the emissions from Euro I to Euro V, that will be introduced in a few weeks, has contributed to the improved air quality in our cities.
In many areas the bus fleet is of varying age. The old buses cause increased cost for society in many ways (health, hospitalisation, absence from work, acid rain, corrosion etc.).
Knowing the impact we now ask: How old should we allow the buses to get before we should replace them?
To calculate the environmental load of hazardous emissions I have been using the key values of the public procurement directive. The result is plotted in the graph below. In the first column you will find the environmental load of a bus fleet where the age of the buses is evenly distributed from 1995 to 2009, 10 buses purchased each year giving a total of 150 buses. In the second column the bus fleet is not allowed to have any buses older than 10 year giving 15 buses each year distributed from 2000 to 2009. In the third column all 150 buses have Euro V status and in the last column we compare to a fleet with hybrid buses.
In the next blog I will include the cost for carbon dioxide and energy use in the calculation to show total cost efficiency for society.