Now, for someone with a CDL license, idea of engine braking shouldn't be foreign. I thought it is part of a CDL test (a practice test I just found had that as question #3).
I think we can take it for granted (though of course this should be checked, just to ensure that due diligence is done) that at some point, as part of the CDL A licensing process, the driver would have been required to demonstrate knowledge of engine braking on a
written test. But:
* There is a difference between showing knowledge of something on a written test and being willing to apply that knowledge on the road, either in a driving test setting or once licensed.
* Experience applying engine braking on one type of vehicle does not guarantee that the driver will know how to use it on another type of vehicle, even if both vehicles are covered by the same license category or by the same endorsement within a given category.
In regard to the latter point, the example that comes to mind for me is a friend of mine who, like me, had a Kansas noncommercial class C driver's license. By many criteria he is a better driver than I am--he learned on a manual and has much greater motor fluency, so he is able to handle higher speeds safely, and achieves vehicle sympathy naturally while I huff and puff at it. Yet, on a family vacation in the early noughties, he smoked the brakes on a minivan going down the 10% grade on US 14 Alternate in the Big Horn mountains in north-central Wyoming. I expressed consternation that he didn't downshift, explaining that I had gone down the same grade twice in low gear without having to tap the brakes except for hairpin curves. He told me that he would have done so in a manual, but the minivan was an automatic and he had not known downshifting for engine braking is also possible in automatics.
In order for having a CDL A license with the correct passenger endorsement to improve the driver's chances of negotiating the NY 30 hill with engine braking, I think the following would have had to happen:
* Passenger endorsement requires both a written and practical test (not just a fee)
* Practical test can be taken only at a CDL testing center near steep hills, over a testing loop that involves a hill descent for which the candidate is expected to demonstrate knowledge of engine braking
* Candidate is required to take the practical test in the specific vehicle he or she will be driving with the endorsement, if it is granted
New York is not a flat state, but even there I think it would be difficult to channel all CDL applicants through a testing process that requires actual demonstration of engine braking. In a state with very restrained topographical relief like Kansas or Florida, it would be well-nigh impossible.