Here’s why some fleets choose propane autogas over their CNG cousin:
An autogas station has an environmental footprint that is about a tenth of the size of a CNG station due to the electricity required to store and pump CNG.
Natural gas (methane) generates fewer greenhouse gas emissions per British thermal unit (BTU) than propane, but methane is chemically stable when released into the air and produces a global warming effect 25 times that of carbon dioxide. Propane’s short lifetime in the atmosphere and low carbon content distinguish it from other fuel sources as an important energy option in a carbon-constrained world. (Source: PERC Propane Reduces Greenhouse Gas Emissions: A Comparative Analysis 2009)
For even more advantages see below: