My long-term, and perhaps incorrect, impression is that they were Emergency brakes when they were capable of stopping the car from at least at a relatively slow to moderate speed. They got called Parking brakes when they were less effective and basically only effective at holding at rest an already stopped car.
They may be called parking brakes, but Iâll use it if I have hydraulic brake failure.
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There are not two brakes. The emergency/parking brake is a hand lever or foot pedal that applies the rear brakes using a cable, even if the hydraulics go out (hence the emergency name); the thing in the transmission (automatics only) is the parking pawl, which locks the transmission once you are stopped; it will not stop a moving vehicle, and damage may result if you try it.
For several years, it has become fairly common for new cars to come equipped with a simple push button that applies the e-brake electrically via small motors adjacent to the rear wheels. No more hand lever, foot pedal, or cables leading from the cabin to the rear wheels.
You can lock a manual transmission vehicle also. Put it in 1st. Or if facing downhill, put it in reverse.
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I guess you either donât know anything about bigger trucks and or motor homes or you have no idea what I was talking about⊠Try reading what I said again a little closerâŠ
I have built transmissions off and on for over 30 years, I think I might know what a parking pawl (and for the smart ass that called me out cause I didnât hit the L last time this one is for you 
) is thank you⊠
Any more question as to what I had said now or do you understand what I meant by it???
âI guess if you wanted to really break it down a parking brake is used on the back (end) of a transmission on a larger vehicle (motorhome big truck etc) and an E-brake is used in the rear brakes somehowâŠâ
BTW: The reason for using a Parking brake on the back of a transmission instead of a built-in Parking Pawl (look I did it again) is due to the weight of the vehicle, you would never be able to get it out of gear only using the parking pawl, if you have ever gotten a heavy car stuck in park on a hill and could not get it out if park then you will understand this betterâŠ
Of course, but letâs not forget that Chryslerâs e-brakeâat least up through the '50sâwas installed on the drive shaft. It was actually very effective, even thoughâI thinkâthey may have been the only car company still using that technology by the '50s.
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Effective, yes, but it has some ugly failure modes. Such as; Broken driveshafts, differentials or axle shafts (full-floaters) means you have no e-brake. If you have an open differential and one wheel is on dirt, gravel or ice and the other on pavement, you have no brakes either. Thatâs why most migrated to brakes at the wheels.
The trans brake was a common foot-brake operated basic early braking system. Used on cars from Model Ts to Rolls Royce. Supplemented by a hand brake.
And then there was Saab⊠Emergency/parking brakes on the FRONT wheels! Like my 1971 99E (with electronic fuel injection!) Yes, little drum brakes inside the disk rotor. Saab figured (correctly) theyâd be stronger and safer on a FWD car than on the rear.
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I was in that situation. Bad brake repair at the shop; I returned having to use the hand brake while driving. This was a 1966 Chevy: cable to the rear brakes. In these Modern Times, I have been in the situation with a locked e-brake and a dead battery. Go and push it to the side of the road!
Also, âpawlâ guy: you have made your point. Just trying to tow the line.