Using a multi­period optimization model based on lineal programming, which integrates energy, economy and environment dimensions (MARKAL – Standard version), some economic and environmental impacts due to five different technological choices for the omnibus fleet of the Rapid Bus Transit (Metroplus System) which will operate at the metropolitan area of the Aburra Valley (Medellin – Colombia) were estimated. The technological choices compared are: (1) a fleet powered by compressed natural gas, (2) powered by diesel, (3) powered by EuroDiesel III imported from the Mexican Gulf, (4) powered by a mixed fleet 50% compressed natural gas and 50% diesel, and (5) a fleet powered by hybrid diesel vehicles. Results outstand the economic and environmental benefits associated to the use of an omnibus fleet powered by compressed natural gas.