2 questions about Diesel in U.S.A.

[Colly0410]

My brother-in-law who's a taxi driver refuses to have a diesel car, he tried one but it cost so much to get through the taxi roadworthy/emissions test every year that his next car was petrol/gasoline. Doesn't get so many miles per gallon as a diesel but less costly to maintain. The annual taxi test is much stricter than a normal cars annual MOT test, slightest defect that would pass or be a minor advisory notice on an MOT test will fail the taxi test...