Is a driver who misses congregational prayer due to his work considered a traveler [for whom concessions apply], or is he obligated to leave this job?

Congregational prayer in the mosque is obligatory for every able-bodied man. If the time for prayer comes, perform it in the nearest mosque, unless doing so would cause harm to your livelihood, in which case you are excused from attending. You are not considered a traveler unless you have covered the distance for qasr (shortening prayers), which is 83 kilometers or more from the edge of your city or place of residence. There is no blame upon you for remaining at your work, but you must perform the congregational prayer in the mosque unless attending it would result in a legally recognized harm that permits you to be absent from it.