GMC 1999 Sierra 1500 Pickup Owner's Manual page 186

Your Driving and the Road
Traffic Lights
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We're all familiar with traffic lights or stop lights. Often, green arrows are
being used in the lights for improved traffic control. On some multilane roads,
green arrows light up, indicating that traffic in one
or
more lanes can move or
make a turn. Green arrows don't mean "go no matter what." You'll still need
to proceed with caution, yielding the right of way to pedestrians and
sometimes to other vehicles.
Some traffic lights also use red arrows to signify that you must stop before
turning on red.
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REVERSIBLE
LANE ON
ROADWAY
MULTI-LANE
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Many city roads and expressways, and even bridges, use reversible-lane
traffic control during rush hours. A red X light above a lane means no driving
in that lane at that time. A green arrow means you may drive in that lane.
Look for the signs posted to warn drivers what hours and days these
systems are in effect.
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