RE: The price differential between If it's the case, it makes economical sense to replace old diesel trucks by new Natgas ones at a rate of 15% per year. Then there is the issue of development of a Natgas supply stations network on the highways and the safety issue to deal with (EPA).
After all, if Natgas usage is not more widely spread across the US, I suspect foul play. Would it be possible the EPA, known to be bought by the oil industry, is blocking the development of Natgas usage in the auto industry?