I dealt with a company in the UK once that had CNG in their plant and they installed a refueling station. They worked out that they would need a fleet of 30 trucks running on CNG to justify the cost of installing the station. I can't remember if they were running on one or two shifts though. There's a company called gaspoweruk that do the conversions. They maybe able to give you some figures?
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.