First experience with the Pre-Collision System

So I thought I'd chip in my experience with the Pre-Collision System... first thing's first, no I didn't crash and no it didn't auto-brake for me (i.e. it wasn't an "omg I'm gonna have an accident" scenario).


Scenario:


Two lanes of traffic, I'm on the left lane and we're heading to an underpass (very short. It just goes under a railway bridge).

It's bright and sunny but kinda dark under the bridge (Road dips under a railway bridge that's level with the ground). I was doing about 60km/h give or take. As I emerged from the underpass, I was distracted (can't remember what I was looking at). When I looked forward again, I noticed that the car in front had brake because there was a car attempting to turn left. I had enough time to brake but given that I wasn't looking forward prior to the vehicle ahead of me braking, I kinda panicked so I quickly pressed the brake.


1. Car sensed an emergency stop because my foot came off the accelerator quickly. Brake Assist kicked in


2. Car came to a very quick stop (I'm impressed!!) with a quick tyre squeal and ABS kicking in. I didn't come to a complete stop because, like I said above, I had plenty of space. I just had a reflex action to the brake lights ahead and the vehicle ahead of me nearly stopped so I did release the brake pedal when I realised that the Prius was stopping a lot shorter/faster than I needed to.

3. PCS kicked in (no "BRAKE!" warning or beeping or anything like that). The seatbelts tightened (I heard the electric motor whirled as the seatbelt held me right against the seat but honestly, it didn't click in (no pun intended) until I came to a smooth stop behind the car. I was thinking, (whoa, the seatbelt's a little tight. On a normal car, the ELR [emergency locking retractor] would've released the tension the moment I returned to my position but I'm sitting right now in my normal driving position and my seatbelt's still tight)

4. A few seconds after I stopped, I heard a whirl and the seatbelts released the tension.


What did I learn from this?

1. Don't be distracted cause things change in a split second (i.e. the car in front moving at 60km/h to coming to a full stop)

2. Trust the Prius' brakes. They WORK and they work really well.

3. PCS is always looking out for you and works even without the auto-brake or "BRAKE!" warning.



It'll also be interesting to test if the seatbelts tightened because the car sensed there was an object in front or whether the seatbelts will tighten whenever you do an emergency stop (regardless of whether there's a car in front).


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Edit: It will activate even if there isn't an object (e.g. car) in front. All you need to do is do an emergency stop.


Disclaimer: I'm not responsible for any injury you may incur during this experiment. Attempt at your own risk and preferably not on a full stomach or if you're pregnant.


1. Bring your Prius up to a constant speed on an empty road (I chose 60km/h).

2. Check your mirror to ensure there's no vehicles behind you. Lift off the accelerator quickly and press the brake pedal (doesn't matter how hard you press the brake pedal. The key is lifting off the accelerator quickly to make the car's cpu think it's an emergency brake and thus activate Brake Assist. You could do a full ABS stop if you wish but it's not necessary).

3. Depending on the speed you're travelling and how hard you're braking and a whole host of other variables that I can't possibly list, the PCS may activate earlier or later (we're talking split seconds here). I did two attempts earlier this evening and they activated at different times (i.e. the first I was leaning forward a bit before the seatbelt caught me, the 2nd time, it caught me before my back left the seatback)

4. If you didn't realise that PCS activated, you should by now as you release the brake pedal (you don't have to come to a complete stop. You'll know what I mean once you see it in action). You should hear a motor whirl/buzz noise in your left ear as the seatbelt tension releases.


Again, be prepared (and forewarned)... it does pull tight.


Like the video that XMAN LIVE made (found here), it feels like someone's doing CPR on you.

 

It does apply the brakes automatically but at that point, you're gonna crash anyway (we don't have the latest and greatest PCS that will come to a complete stop *before* the object)... It will reduce the speed of the impact though.

+1. A safety feature definitely worth getting. Just like airbags, you wish you'll never have to use it but it's nice to know it's there (and that it works in more than just the depicted scenario in the video)

Yes. It's more sensitive if the car ahead is moving. If the car ahead is stationary, it'll take longer to recognise cause it can't tell if the object ahead is a car or just a metal railing (e.g. an offramp)

Did it hit the styrofoam?

. Hopefully Toyota can bring the price of the technology down even further (and soon) so that others benefit from this.

 

Edited the first post. I did try it again on an empty road. PCS will activate the seatbelts even if there isn't a car in front of you (and definitely without DRCC). Instructions above if you want to try it for yourself.