Leaving car in gear while parked- yes or no?

It is quite an entertaining subject this, and just shows how wide a spectrum of skill and in understanding of the mechanics there is amongst the licensed driving public!

There is of course no right answer for everyone. There may be a more consistent answer if we were discussing just one make and model.

I have driven so many different cars that I long ago lost count. Thesedays I hire a different one almost every week and they vary quite a bit in the handbrake department. Some are manual, some are auto. Some are an interesting mix or something else! I am thinking of a 9-tronic Merc at one end, and a Toyota hybrid at the other. The Merc I would generally trust to sort itself out as its onboard computers are the business. The Toyota I would set the handbrake in most cases.

Fairly obviously, automatics should be left in "Park" but many modern ones do that automatically when they recognise you have switched off. Whether you use the handbrake depends on whether you are a letter of the law fanatic, or can make a reasoned judgement based on your knowledge of whether the car can possibly move on the slope you leave it on.

Older manual cars are probably the main thing we are talking about in the thread. I almost always leave those in first gear on the flat with no handbrake if I am leaving it for any length of time. I add modest tension handbrake if there is any noticeable slope. If it is a very steep slope I also give an extra notch on the handbrake, steer into the kerb, and I might even select reverse gear instead of first.

Some handbrakes, even on more modern cars are very mickey mouse ... not so much long levers with buttons, but silly switch-like controls (but nevertheless mechanically operating). I am thinking of a Citroen I used to own moons ago which "let go" when the missus parked it on a steep slope. She always made sure it was left in gear too when parking after that.

I too am conscious of the possibility of a less conscientious driver jumping into a manual car after me. If I know it is a possibility e.g. when returning a hire car or handing over a car to a neighbour, I do not leave it in gear (to avoid exactly the sort of accident that MataNui describes). In that case, if I have to leave the vehicle on a slope, I might give it an extra notch on the handbrake.

I would never leave my own car for any length of time with handbrake yanked on needlessly. As has also been said, many brake mechanisms can get semi-locked on/stuck on especially in damp cold winter conditions.

And just to add an alternative not yet discussed, I have another vehicle which is long term stored in a large building with other vehicles. In that case I leave it out of gear and no handbrake on so that third parties could push it or tow it out of the way if there was a fire for example.