ABSTRACT
The stock-flow-service nexus approach is used to analyse the interactions that occur between energy/material flows, material stock and energy/material services. The latter identifies the functions that energy and materials contribute to society. Using a Colombian bus rapid transit operator as a case study, this nexus is applied to a corporate setting in order to evaluate environmental performance via five nexus indicators. During the 11 years studied (2001–2011), the bus company’s fuel efficiency increased by 5%, going from 1.851 to 1.948 km/kg. Stock efficiency improved 35%, going from 5.7×104 to 7.6x104 km/bus. The interquartile range of stock evolution, which is the variance between the first and third quartile of the distance travelled by each bus, reduced from 40,426 to 22,070 km. This demonstrates improved fleet management practices. However, this came at the cost of increased waste generation. In fact, service provision per unit of waste outflow decreased by 47%, going from 65 to 34 km/kg. Similarly, the annual fraction of waste relative to a unit of vehicle stock went from 10% to 25%. These opposing trends highlight the difficulty of improving overall environmental performance and shows the considerable value and challenges of using a nexus perspective as part of a management system.
