The lack of funds has also complicated the introduction of cleaner vehicle technologies. While the entity would ideally have substituted a higher percentage of buses run on compressed natural gas (CNG), only 72 of the fleet of 1 360 buses have this kind of engine. Expansion towards the suburban areas in the State of Mexico has become increasingly necessary, and transport services need to provide a denser network, with alternative itineraries for corridors that are close to or above capacity.