When you use your left foot, your stopping distance is dramatically shorter
I want to be clear here: the No. 1 factor in stopping distance at a given speed is reaction time, and by far the best way to cut down that time is to pay complete attention to the road around you. But even with zero distractions and a quart of coffee pumping through your veins, using your left foot to brake will save you valuable time (and thus distance) in an emergency.
A brilliant study from the University of Iowa establishes total driver reaction time as 2.2 seconds, and finds that the average driver will begin lifting his or her foot off the accelerator 0.96 seconds after the need arises. That means that the act of moving your foot over to the left, then pushing down on the brake pedal, requires an additional 1.24 seconds for that 2.2-second total. That's huge.
Meanwhile, it takes 1.64 seconds until drivers start to steer. Total. I'm willing to grant that it will take a fraction of a second to push down on the brake pedal even with your left foot, and I'll even go high here for the sake of argument, and allow that it's the same 1.64 seconds (total) to push on the brake with your left foot as it is to start to steer. Most people brake before trying to steer, so this actually skews the numbers, but the result -- saving 0.68 seconds -- is still absolutely convincing when you look at the distance that saves you over right-foot braking.
At 70mph, you cover 102ft, 8in per second. Over the course of the 68 hundredths of a second that a right-foot braker wastes, his or her car travels a full 70ft. Amazingly, that number (in feet) is going to remain tied to your speed in miles per hour. Going 45mph? You're saving 45ft with your left foot in an emergency, etc. Pretty cool, right?
Going back to our example with Rocky, when I missed him by around 5ft, I was going just over 40mph. He's welcome.