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No way. When I was 15, my father taught me never to trust my mirrors and
always to turn my head and look before changing lanes. It's always worked
for me -- not gonna stop now.
That's how almost everyone else was taught too. As I said in an above post,
I have driven with my side mirrors angled out ever since I started driving.
I also do not shoulder check at all, there is no need.
You may be singing a different tune if either one of two things happens to
you:
1) Someone in front of you on the highway decides to slam on their brakes a
split-second after you decide to look backwards going 70+ MPH (IE, trying to
pass them). You get a big surprise when you start looking forward again.
With the technique mentioned, you never have to take your eyes off of the
road in front of you, this is much safer. While moving your eyes to either
side mirror (which can be done a lot faster than the fastest of shoulder
checks), your peripheral vision will still allow you to notice brake lights,
speed differences, objects in roadway, etc.
2) In any kind of emergency situation in which a lane change would be the
only way to avoid an accident, you will either have to shift lanes quickly
without shoulder checking and pray no one is in that lane, or you will have
to hit whatever is in front of you. In a lot of situations, you won't have
time to do both. Shoulder checking takes way to long.