What is the test for hiring a 40 year old bus driver?

In Hodgson v. Greyhound, 499 F.2d 859 (7th Cir. 1974); cert. denied, 95 S.Ct. 805 (1975) the two pronged test was approved in safety related cases and referring to the nature of the occupation at page 863; ... (a) public transportation carrier, such as Greyhound, entrusted with the lives and well-being of passengers, must continually strive to employ the most highly qualified persons available for the position of inter-city bus driver for the paramount goal of a bus driver is safety. Due to such compelling concerns for safety, it is not necessary that Greyhound show that all or substantially all bus driver applicants over forty could not perform safely ... Greyhound need only demonstrate however, a minimum increase in harm for it is enough to show that elimination of the hiring policy might jeopardize the life of one more person than might otherwise occur under the present hiring practice.