[doikor]

> If there's 400,000 new commercial driver's licenses every year then how many existing commercial driver's licenses expire / die / move to a different job / whatever?

I don't know how the licenses work in US but here in Finland a lot of people have truck drivers licenses and the permits to do it commercially (2 different things here) but do not actually work in trucking in the traditional sense.

For example got a friend who has those as he works construction as a crane operator. He needs the licenses/permits to be able to move his crane which is classified as a truck when driving on the roads to move it from site to site. Another one works in selling earth/dirt. He needs the licenses to drive his own truck to move stuff around the quarry (required as it is not fenced and gated off from public roads). Also loads his loader on the truck to move it between the sites he owns as needed.

Also a lot of people go into the field for a year or two and quit as it is hard work with long/bad hours and thus miss out on family life etc.