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When my brake pedal travels to the floor...

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In my current car (automatic transmission), if I step on the brake and the pedal goes to the floor (yikes!), I can grab the handbrake and pull it, also shifting into 1/2 for additional engine braking.

What do I do in the S? No handbrake, no emergency footbrake. Where's the backup brake in the Model S? Not sure if regen is enough to qualify...
 
Shouldn't happen in the first place. Cars have two independent hydraulic systems going to opposite corner wheels. If this happens you've probably been ignoring a nice big red warning light on your console for far too long.
 
Thanks. I'm feeling a bit stupid now. How long have cars had independent hydraulic braking systems?

The Model S actually has a completely separate hydraulic e-brake that is separate from the dual opposing-corner system. It even has it's own caliper and pads. It is activated by a control on the touchscreen. I have a similar concern about how you modulate the amount of e-brake you want to apply. For example, is the touchscreen control a large button or a slider control?
 
Thanks. I'm feeling a bit stupid now. How long have cars had independent hydraulic braking systems?

Longer than I've been driving cars. Here's a typical "dual diagonal" system (diagram from here):

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The Model S actually has a completely separate hydraulic e-brake that is separate from the dual opposing-corner system. It even has it's own caliper and pads. It is activated by a control on the touchscreen. I have a similar concern about how you modulate the amount of e-brake you want to apply. For example, is the touchscreen control a large button or a slider control?
Are you sure it's hydraulic? I'd guess its operation is binary, rather than something you can modulate.
 
I once had the brakes go completely unresponsive in my prius (pedal all the way down doing nothing -- felt like all the pressure went out of the pedal). turning off the car and back on brought it back, and luckily when it went out I was going uphill at an off-ramp that naturally slowed me enough to have time to think. (of course engine break mode and emergency brake near at hand there too...)
 
It's electric, not hydraulic.

I was told by a Tesla tech (which may or may not make it accurate) that it is hydraulic. The hydraulic system is activated by an electric actuator of some sort. He also said they have to flush the e-brake lines along with the regular brake lines at prescribed intervals. Accurate? Don't know. But this I know to be true: You can definitely use it at any speed as it is designed to be used as an emergency brake, not just a parking brake. This was confirmed by Tesla in public comments to the NHTSB.
 
Ah, that looks like the same sort of servo actuated parking brake as on newer Audi's.

At a high performance driving school I had an instructor pull up on the electric e-brake on my S4 while I was turning on the skid pad, hoping to lock up the rear wheels and induce a spin on me. The car just slowed itself down quickly to a stop, perfectly controlled while still turning. :)