Nowadays natural gas is one of the most used alternative fuels. With the putting into operation of technical vehicles with the Compressed Natural Gas (CNG), an ecological project starts in Prague, whose aim is to gradually replace the diesel propelled vehicles for ecologically propelled vehicles. The new CNG propelled vehicles are used for street servicing, garbage collection and cleaning. Except for the ecological propulsion, these vehicles are equipped with the dust catcher for the particulate matter (PM-10). All these vehicles will be used mainly in the most polluted areas, which is the centre of the City. The advantages of this fuel are the reduction of emissions and a lower noise in traffic. The security of the traffic is fully guaranteed. The operating cost of CNG is half of the cost of petrol or diesel.