Emergency braking - eh?

[Pica-Pica]

Driving on a dual carriageway, absolutely clear, a pelican crossing light goes amber. Nothing in front, and I knew nothing was behind, so clear all round. I could have legitimately gone through, but decided to stop (as I said, clear all round).

So a sharpish stop. Then I can hear the indicators clicking. I then realised that the sharp stop had triggered the hazards. I know this happens (and brake lights flash), I was just somewhat surprised that it occurred at what felt a sharp but not fierce stop. It could be that the car was actually stopping sharply, but felt very secure and safe doing so, and therefore seemed slower than the stop really was. I feel I want to practise a few quick stops to check it out at various levels of deceleration.

Anyone experienced this? This was a 335d.

[Pica-Pica]

Max_Torque said:

Pica-Pica said:

Driving on a dual carriageway, absolutely clear, a pelican crossing light goes amber. Nothing in front, and I knew nothing was behind, so clear all round. I could have legitimately gone through, but decided to stop (as I said, clear all round).

So a sharpish stop. Then I can hear the indicators clicking. I then realised that the sharp stop had triggered the hazards. I know this happens (and brake lights flash), I was just somewhat surprised that it occurred at what felt a sharp but not fierce stop. It could be that the car was actually stopping sharply, but felt very secure and safe doing so, and therefore seemed slower than the stop really was. I feel I want to practise a few quick stops to check it out at various levels of deceleration.

Anyone experienced this? This was a 335d.

What triggers the system is not just the rate of deccel, but the speed at which you stop braking! If that is bellow about 20mph, the system triggers at a lower deccel threshold, because you have become a 'stationary Hazard' in the road. You can do a full threshold brake (1g) and as long as you stay about roughly 20mph the brake lights wont' come on (so the systems doesn't generally trigger on track etc)

Hmmm. I shall have to experiment on a clear road. As I said it was not an uncomfortable stop, I stopped firmly because it was safe to do so. I don’t recall feeling a harsh stop at the end, as I eased off the pedal. I will experiment some more!

[Pica-Pica]

Byker28i said:

It was your BMW running a systems check to see if the indicators were working as they hadn't been used for a while. It ensured noone was around before it performed this test so as not to embarrass you.

I assure you, I make all necessary signals (and no unnecessary ones), unlike many police cars whose drivers seem to have forgotten to think about the need for informing other road users of their intentions. Sorry to spoil your ‘joke’.

[Pica-Pica]

Fastdruid said:

Max_Torque said:

What triggers the system is not just the rate of deccel, but the speed at which you stop braking! If that is bellow about 20mph, the system triggers at a lower deccel threshold, because you have become a 'stationary Hazard' in the road. You can do a full threshold brake (1g) and as long as you stay about roughly 20mph the brake lights wont' come on (so the systems doesn't generally trigger on track etc)

I thought one of the triggers was the time taken to go from accelerator to brake. ie if it is planned you take a leisurely move from one to other (or going from fully off the throttle), if it's unplanned (emergency) then you're straight off the accelerator and then on the brakes...

I think mine is meant to only trigger hazards at motorway speeds (its a 2008 Mondeo so doesn't have all the low speed avoidance etc that more modern cars have).

I know I've triggered mine inadvertently in a "full bore, straight to hard brakes" move before.

I assume that if you are on cruise control, and foot off acc pedal, the system will recognise that as being 'under power'