[spookthesunset]

> In many places alternate routes were created for people towing heavy things.

That, uh, sounds pretty inconvenient!

So without engine brakes if you downshift in an older diesel does the engine just rev right up and the car doesn't even bother to act like it is slowing down? That has to be pretty weird....

[mcguire]

Eastbound on Interstate-40 on the eastern slope of the Appalachians the truck speed limit at the top of the pass is 35mph and there are very, very many warning signs including radar-activated lights. There are also three or four runaway-truck ramps (filled with loose gravel) that are somewhat frequently used, and often trucks pulled over to the side to let their brakes cool.

(The Rockies have even more of this sort of thing, but I haven't been out there in quite a while. :-( )

[BenjiWiebe]

It very much slows down. Just not quite as much as a gas engine. You still have friction losses (especially as you get higher rpm), losses from alternator, water pump, engine fans, oil pump, etc.

One of my vehicles is a VW Jetta TDI (diesel, ALH engine).

[frosted-flakes]

TDIs have turbos.