I can drive 55 because it's more
efficient and safer right hey there
grandma drivers this is big rig science
Pappy trace for dnews what's your 20
old cars and highways often have a speed
limit of 55 because of efficiency it
started in 1973 when the US was under an
oil embargo to conserve resources
Congress tied the state speed limits to
federal highway funding basically
forcing states to adhere to 55 or else
they'd lose millions and highway money
they picked 55 because the Argonne
National Laboratory do a lot of traffic
research found that that was the speed
most cars would get the best miles per
gallon
once the embargo ended Congress was
reluctant to lift the limit until 1995
afterward states went on a tizzy
trying to pick new speed limits most
chose 70 but some chose 65 or 80 yes
Texas I know you got a little bit of 85
up in there you get a cookie whatever
but how did they decide on those numbers
well firstly exceeding the speed limit
or driving too fast for the conditions
is the primary cause of auto crashes
globally which is why we have speed
limits in the first place but it's
important to know too fast for
conditions that's a big deal
because speed limits are determined by
data but the data is from three main
things nature engineering and humans
obviously this is all a simplification
is complicated stuff but for example
when highway and traffic researchers
decide a speed limit they take into
account the weather visibility terrain
the location of the road and so on
that's the nature they also take into
account the purpose of the road crash
risks traffic and truck flow monitors
those little rubber tubes you sometimes
run over on the road what the road is
made of the amount of shoulder next to
the road maintenance schedules that's
the engineering and of course how humans
actually use the road which we'll come
back to in a second they then take that
data and they use different computer and
cost based models to specifically pick
the speed for that stretch of road the
human component has a lot to do with
safety but also our ability to actually
drive on the road at that speed the
operating speed model is often used it's
sort of crowdsources the speed limb
using something called the 85th
percentile rule basically researchers
observe the average speed people on a
road naturally want to use and they lob
off the speediest 15 percent research
has shown that the 85th percentile is
the speed most people would be
comfortable driving which is super
important because be at 55 or 85 the
researchers and lawmakers want a speed
limit that is quote accepted as
reasonable by a majority of road users
so Nature engineering and humans
together factor in to how we pick speed
limits and all of that kind of makes
sense you know faster speeds tend
towards stretches of road in like
Montana or Texas or Australia where
roads are more open its sparsely
populated the roads are straighter while
denser high-traffic urban areas with
more weather considerations those tend
towards slower speeds duh right speed
limits are ultimately human things but
they're based on physics plus biology
faster speeds mean less time for our
animal brains to react when something
goes wrong
according to the European Road Safety
observatory for every one kilometer an
hour increase in speed there's a 3%
increase in crashes it's an old saying
that it's not the crash that kills you
but the sudden stop at the end the
faster you're going the data says the
more kinetic energy is in the vehicle
and the worse the crash is gonna be this
is why some regions likely have lower
speed limits for their conditions roads
and drivers once the speeds are picked
researchers are constantly going back
and adding new data and testing the road
at various speeds and in various
condition look everyone who drives a car
wants to get where they're going as
efficiently quickly and safely as
possible even traffic researchers but
every Road and every type of road is
different the reason that that speed
limit is on that road is a mix of lots
of data and lots of human effort it also
takes a lot of effort to keep your car
clean tech run by Chevron's patented
precision clean technology targets and
removes deposits left by lower to your
gasoline it bonds with and breaks apart
carbon deposits more effectively than
other additive technologies tech Ron
gets into the deepest parts of the
engine where the most destructive
deposits build up and sweeps them away
but what about self-driving cars should
they have speed limits too are they even
safer sources say the cars have been
rear-ended mostly but they've also been
sideswiped and hit by a car that ran a
red light or a stop sign since the crash
specifics
our secret we can't be entirely certain
but Google says that the car was never
at fault what do you think should speed
limits be higher lower you just waiting
for the self-driving revolution let me
know down in the comments make sure you
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of them and thanks for watching