Diesels are freely available in UK.
They do get much higher mileage - sorry, I don't know the price difference between diesel and petrol (gas) for a relative cost comparison. If it is something that saves the individual motorist some money, Gordon Bennett will probably increase the tax on it.
Unsure about the environmental impact, in the old days diesels were notorious for belching black smoke and being very noisy - this does seem to have been cured.
I suspect that all emissions, whether diesel or petrol, are harmful to us.
I was intrigued about this "auto industry lobby" - is it another of those protectionist dinosaurs that "brown bags" senators and representatives for their clients?
If it is, the result of that protectionism is IMHO a bit of a two edged sword:
1. in the short term, it keeps the underperforming senior management and union leaders (who have failed to keep up with the market) in their highly remunerated jobs at the expense of the consumer and modernisation.
2. in the long term, it kills off the industry and loses most (if not all) the senior management and the union members their jobs because the industry was not kept up to date and competitive in the market place - and even worse, the country takes a big hit in its foreign trade balance of payments and ultimately the value of its currency.