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Here on the internet people just explain the difference between the two and how you should also apply the handbrake when it gets steep, but why is there even a parking gear in the first place when you can just use the handbrake?

Peter
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    Interesting question. Especially from the point of someone one from Europe where most cars seem to use regular gears instead of automatics and the park position does not even exists. – Hennes Jul 08 '19 at 15:59
  • @Hennes It's so bloody flat around here, we just park in neutral and on the handbrake. Only on hills do we park in the gear reverse to the hill (if pointing upwards, in first, if pointing downwards, in reverse). And yes, that's assuming stick-shifted cars, there's not a lot of automatics around. – Mast Jul 09 '19 at 07:25
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    I'm in New Zealand, where automatics are pretty much the standard (as per the US), and everyone I've just asked puts their automatic in park and applies the handbrake. They all thought it was dumb to just put it in park and not apply the handbrake. Thought you'd might like a view from a different country where automatics are the norm. – Moo Jul 09 '19 at 10:03
  • @Hennes: In a manual parked in (low) gear, the motor is directly connected to the wheels, and so can hold the car quite well. but in an automatic in D, the motor is connected via the torque converter, which is not a mechanical link. So, the motor itself can not hold the car. Though, todays automatics have a clutch for better fuel efficiency, but I don't know if it is engaged when the car is parking. – sweber Jul 09 '19 at 21:19

3 Answers3

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Putting the transmission into "Park" engages the "parking pawl" - essentially a metal pin that locks the output shaft of transmission (and thus the driven wheels) in place.

As to why it exists - it is intended as additional roll-away protection that complements (rather than replaces) the handbrake (which, as the name implies applies actual brakes - usually to the rear wheels). The idea being that if either the handbrake or the pawl fails there's still something to prevent the car rolling away.

Handbrakes, like regular ones wear and thus become less effective with repeated use - and this isn't always immediately apparent to the driver so an extra safety net isn't a bad idea.

motosubatsu
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  • But a manual car can also park with the handrabke while being in a gear. Should the park gear be considered as a perk of automatic gearboxes or is it there to make up for something a manual gearbox would have? – Peter Jul 08 '19 at 16:36
  • @Peter You can achieve a similar result by putting a manual 'box in gear when parked - although IMO "Park" has the advantage here since you aren't risking forgetting to take it out of gear and unexpectedly lurching/stalling. – motosubatsu Jul 08 '19 at 16:54
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    @motosubatsu complement not compliment - the handbrake is not polite to the gearbox... just for info, plus 1 from me... – Solar Mike Jul 08 '19 at 17:54
  • I have often seen the "parking pawl" described, as in this answer, as a "metal pin". And ever since I saw it so described I've wondered how damn strong this metal pin is? Because sometimes, on a hill, when I shift to park and then take my foot of the brake the car shifts and there's definitely a shock as the "pin" takes the weight of the car - and I wonder: Will it ever break? Can it wear out? – davidbak Jul 09 '19 at 00:57
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    @Peter An automatic transmission will never be secure while in gear with the engine off like a manual will. That's because of the torque converter. The pawl is the only way to lock the transmission in a fixed position. – Logarr Jul 09 '19 at 02:29
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    @davidbak yes those pins can shear through, and have done before... This is why the handbrake is the primary system and pointing the steering wheels appropriately is also advised. – Solar Mike Jul 09 '19 at 05:40
  • @Peter: The general advice for manual cars in my experience has been that if you park on a hill, you're still suggested to put the car into (forward/reverse) gear, which achieves the same effect as the Park gear on an automatic. It's not a requirement, just a matter of safety net. – Flater Jul 09 '19 at 08:43
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    @davidbak indeed..the "shock" you mention is the reason why the handbrake should be applied before engaging Park if you are on a slope. – motosubatsu Jul 09 '19 at 08:51
  • @SolarMike good catch! I've corrected the spelling. In my defense I'm a little under the weather this week! :D – motosubatsu Jul 09 '19 at 08:57
  • With manual cars I have always learnt that when it's freezing, it's better to not use the handbrakes, but instead brake using the transmission. Are there similar considerations with automatic cars? – JAD Jul 09 '19 at 09:54
  • The argument that the handbrake will wear with regular use seems a bit nebulous when manual-orientated countries like the UK have no problems using the handbrake many times a day (UK drivers are taught to apply the handbrake in regular driving situations, such as when stopped at lights, pulled over or such, so that any normal trip will include proliferic use of the handbrake) and don't have a problem with wearing them out? – Moo Jul 09 '19 at 10:07
  • @SolarMike I've never heard a handbrake being rude to the gearbox, though. – David Richerby Jul 09 '19 at 10:11
  • @Moo they do wear though, albeit not particularly fast compared with the regular brakes. Hence why the MOT incorporates a check for the efficiency of the parking brake (an absurdly low 16% IIRC), on cars where the pads/shoes are fully distinct from the main brakes it's rare to have to replace them (the cable is a more common maintenance item) but it does happen.The wear is small but it does happen. – motosubatsu Jul 09 '19 at 10:30
  • @JAD While it can happen for a handbrake to freeze on (and an automatic would be no different in that regard to a manual) I tend to think that at least on (relatively) modern cars the risk is overblown - I've certainly never had it happen in nearly 20 years of driving. Relying on the pawl alone if parked on a slope isn't something I'd advise so would err on the side of putting the handbrake on personally. – motosubatsu Jul 09 '19 at 10:41
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    @motosubatsu fair enough. I live in the Netherlands, where slopes don't exist :P – JAD Jul 09 '19 at 10:49
  • @motosubatsu: I've had a frozen handbrake (fortunately when not engaged). What happened was that salty moisture from the road crept in between the cable/sheath and froze when temp dropped to somewhere around -15°C. No way to move that cable. I'd still keep away from using the handbrake for parking (for a longer time, say, over night) in such conditions and rather use wheel chocks. Over here (Germany) this usually happens mostly in hilly/mountainous regions because that's where it gets sufficiently cold. – cbeleites unhappy with SX Jul 09 '19 at 11:34
  • @JAD: OTOH, I expect that it rarely gets sufficiently cold in the Netherlands: the moisture that freezes is usually not pure water but mixed with salt from the road, so the risk of the handbrake cable freezing is much lower around 0 °C than, say, below -10 °C (and the handbrake being fine at -5°C doesn't guarantee that it cannot freeze at -15°C) – cbeleites unhappy with SX Jul 09 '19 at 11:37
  • @cbeleites wheel chocks are an excellent work around where that's a concern :) – motosubatsu Jul 09 '19 at 11:51
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Modern car systems also talk to each other - in more recent cars its impossible to start the motor while the car is in gear. So the gearstick has to be in Park or perhaps Neutral, perhaps with the brake pedal pressed or some other combination.

This is another safety interlock to stop a driver rolling on engine-start because the gearbox was left in a gear.

Of course there are very rare situations you might need to move/bump the car on the starter alone, which is now impossible. The classic Driver's Ed example was "stalled on a railway level crossing with a train coming and motor won't start"

Related How can I move my push-to-start car with the starter?

Also, by putting the transmission into park you're also telling the car its not going to move for a bit, so the computer may choose different courses of action for the engine compared to if you were simply stopped at a red light.

Criggie
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    Well if the systems have learned to talk to each other perhaps is is possible that the gearbox really does -- as motosubatsu says -- compliment the handbrake. – A. I. Breveleri Jul 09 '19 at 00:56
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    @A.I.Breveleri so a possible message could be "piss off, I'm not ready", it would make the codes much more fun to read... :) – Solar Mike Jul 09 '19 at 05:41
  • For manual transmission cars: they often require the clutch pressed to start now, but don't care about gear. – cbeleites unhappy with SX Jul 09 '19 at 11:21
  • @cbeleites thats a design choice from somewhere. A simple manual gearbox should be in neutral and clutch out to keep flywheel engaged to add mass and help turn the engine over. My old landy likes that on cold starts. – Criggie Jul 09 '19 at 12:52
  • @Criggie: first time I wanted to drive such a car I had to ask how to start it - I had automatically made sure the gears are in neutral and didn't even get to the idea that I should clutch (my experience with clutch in/out is mixed: mass vs. turning more stuff in cold transmission oil)... Anyways I think the design decision is OK for cars that automatically shut down the engine when standing (traffic light etc) - then taking the clutch as signal to start the engine again is quite intuitive. – cbeleites unhappy with SX Jul 09 '19 at 13:10
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The two options enable two completely different systems -- in principle, at least,

Putting your car in "Park"

This locks your central transmission into a fixed state, by mechanically freezing the clutch. (Exact approach on how that works depends on the specific model of car.) That means that your wheels are still free to roll -- even on a steep hill -- and you're relying on that transmission-locking mechanism to resist moving.

If you're on anything but a steep hill, then putting your car in "Park" is just fine. Period. Engaging the hand-brake is completely redundant. (And if your car is less than 20 years old, there's a good chance it wouldn't make any difference at all.)

Using the Parking/Emergency Brake

This is basically just a second brake pedal. Pulling on it engages the brake pads on each wheel, as if you were stomping on the brake. Locking it in place is pretty much the same as if you stomped down like that, and then just sat there like that for a couple of hours. (Again, the exact implementation completely depends on the specific model of car.)

If you're actually on a steep hill, then engaging the hand-brake is -- again, in principle -- a more reliable option, since you're now relying on your brake pads to stop your wheels from spinning at all. Those pads are designed bring your car to a screaming stop from 50+mph to zero in a matter of seconds. Asking them to resist the force of slowly rolling down any slope, no matter how steep, is trivial.

Key Considerations

Given all that, there are still some important points to keep in mind...

  1. The underlying concepts of how a car "works" for these are so outdated that they're almost completely irrelevant. All of this guidance stems from a time that "cars" were purely mechanical systems, and questions of how to balance one system against another (like this one) really made a difference in the longevity and performance of a car. Modern cars are such complex, automated entities that this is all very likely moot for any car manufactured in the past 20 years -- I'd be pretty shocked if "putting the car in Park" and "pulling on the handbrake" aren't really just the equivalent of pushing the same button, two different ways, in most modern cars.

  2. None of this is really valuable, compared to the most important single piece of advice for parking on a steep hill...

Curb Your Wheels.

Curb Your Wheels.

CURB YOUR WHEELS.

Laurent Stanevich
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  • I'm pretty sure that on my car (a 2016 Honda Civic LX), the "Park" setting affects only the front wheels, and the parking brake affects only the rear wheels. In particular, on an ice-covered surface, it is possible (but probably a bad idea) to drive with the parking brake set. The front wheels will propel the car forward as normal, and the rear wheels will remain locked. I don't have any particular evidence that the "Park" setting does not affect the rear wheels, but I think it would be awfully weird if it did. – Tanner Swett Jul 09 '19 at 03:06
  • So much waffle, so much wrong. Did you even read the pages you linked to? Because even a cursory glance shows that they contradict your own inaccurate information. – motosubatsu Jul 09 '19 at 09:02
  • How, @motosubatsu? – Laurent Stanevich Jul 09 '19 at 20:29
  • Well, you're wrong that park "freezes the clutch", wrong that the handbrake is redundant except on steep hills, wrong that it's the same as as second brake pedal, wrong that it applies to all the wheels, wrong in your stopping-from-50mph comparison, and wrong that engaging park is the same as pulling on the handbrake. You're correct in the usefulness of curbing your wheels I suppose. – motosubatsu Jul 10 '19 at 08:39
  • Then care to explain your view on how things actually work, @motosubatsu, rather than just yell at other people that they're wrong? – Laurent Stanevich Jul 10 '19 at 11:44
  • I apologize if I've come across a bit harsh - I'm a bit ill this week and it's making me a little waspish. The first link in your own answer does an adequate job of explaining how "park" locks the transmission. And you can see here for an explanation of what a handbrake (or e-brake) is and how it differs in functionality from the main brakes in a car. – motosubatsu Jul 10 '19 at 13:01