They have also estimated that apart from these fuels being less hazardous, they are environment friendly, help in reducing the levels of pollutant emissions and are cost effective. Their extensive use in automobiles will lessen the country's excessive dependence on petroleum imports. They have called for rectification in government policies towards these alternate fuels vis-a-vis petro fuels.

According to a study by K K Gandhi of the Indian Institute of Petroleum (IIP), the high cost of dual fuel i.e. CNG-diesel conversion of a bus or a truck can be recovered in three years for an average substitution level of 50 per cent with CNG and hence this system has proven to be economic.

While arriving at this conclusion, Gandhi has taken note of the fact that the current cost of CNG is more than that of diesel by Rs 1.50 and the cost of converting adiesel bus by CNG mechanical kit is about Rs 1.2 lakh and that by CNG electronic kit is Rs 5 lakh. The cost of manufacturing a fully CNG-run vehicle is expected to be more than two times than that of an ordinary diesel bus.

Despite heavy duty on CNG vehicles, it can be used as a cost effective emission control strategy in regions with low to moderate natural gas prices and moderate to high emission control costs. If improvements in CNG vehicles efficiency is effected it could significantly lower the net cost of its use.

Gandhi, in his paper, further suggested that if CNG carried no tax, there would be circumstances where it would be advantageous, albeit strictly from a net user cost perspective.

Apart from this, Gandhi stated that the savings in pollution abetment cost by use of a CNG bus is Rs 36,345.33 per year causing an annual reduction in pollutants by 837.45 kg. The pollution damage cost in Indian conditions is Rs 43.40 per kg of pollutants.

Similarly, S Sarkar, general manager of Gas Authorityof India Ltd (GAIL), in a separate study, estimated that the conversion of a gasoline-run car to a CNG-run car, which costs Rs 30,000, can easily be recovered within nine months to 15 months based on 30,000 km annual operation and depending upon the fuel consumption of the vehicle on gasoline. He has stated that maintenance costs of dedicated vehicles running on CNG as well as those retrofitted with CNG kits is much less.

Regarding LPG-run vehicles, Gandhi has estimated that the conversion cost for switching over from gasoline to LPG in vehicles can easily be recovered within a period of 18 months in case of three-wheelers and about three months in case of cars and taxis. A reasonable pay-back period is achieved over an average service distance of 50,000 km per annum in case of buses.While arriving at this conclusion, he has taken note of the fact that the cost of LPG is Rs 17 per kg as against gasoline which is Rs 12 per litre. The conversion kit costs Rs 16,000 for three-wheelers and Rs 18,000 for cars.The fuel cost saving is 50 per cent per km. The cost of LPG bus is 10 per cent higher than a diesel vehicle and also the maintenance cost is slightly higher.

Gandhi also stated that alcohol-gasoline blend in scooters, three-wheelers and cars do not require any design change or retrifiment.

In case of buses and trucks using 15 per cent substitution of diesel by alcohol, the conversion cost will be at diesel cost of around Rs 13 per litre for ethanol conversion and diesel cost of Rs 17 per litre for methanol conversion based on ethanol plus additive cost of Rs 11 per litre and methanol plus additive cost of Rs 14 per litre.