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In the US, there are two types of intersections with left-turn arrows. In some of them [the 5-light intersections referred to by Klaatu], the left-turn lanes have a solid green circle light as well as a left-turn arrow . At one of these intersections, a motorist turning left across an on-coming traffic
lane is required to give way to the traffic on such a lane but may proceed without interruption when no such traffic is apparent. Additionally, a motorist expecting to turn left is allowed to enter the intersection before the way is clear for him to proceed, provided he does not actually enter or cross the on-coming lane until it is safe to do so. Unfortunately, this design of intersection can have problems if an on-coming vehicle is approaching as the light turns yellow while another vehicle is in the intersection waiting to turn left: if the left-turning vehicle waits until the on-coming vehicle either passes through the intersection or stops, it will delay the cross traffic; if it proceeds in the expectation that the on-coming vehicle will stop, it may get sideswaped if the on-coming driver tries to beat the light.
To avoid these problems, some intersections prohibit left turns except when a green left-turn arrow is lit. Even if there is no other traffic around, a motorist seeking to turn left is required to wait until the signal gets around to illuminating the left-turn arrow. This avoids the hazards associated with the solid-green light, but can impose significant and needless delays on left-turning motorists when traffic is light.
I would offer, as a compromise between these two types of intersections, a flashing red left-turn arrow. In general, a flashing red light means to stop, and enter the intersection only after it is safe to proceed. Thus, in this context a flashing red arrow would require people turning left to stop at the intersection and not enter it until traffic was clear enough to allow a left turn; if traffic were to clear sufficiently before the main light turned red, a motorist would be allowed to proceed without having to wait for the green arrow signal, but if traffic did not clear the motorist would be required to stay out of the intersection.
Such a signal would avoid the safety and efficiency problems of the five-light signal, while avoiding the needless delays imposed upon motorists during off-peak hours by the green-arrow-only signals.
5-light traffic controls
Baked where I come from. [Klaatu, Oct 05 2004, last modified Oct 17 2004]
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||I could swear I've seen flashing arrow lights
||The 5-light traffic light is baked. <link> When the light first changes, you get a green arrow which, after a period of time, then goes to a yellow arrow. After that, it changes to solid green for left turn yield.
||I'm very familiar with the five-light traffic signals. But many intersections around here have replaced them with dedicated left-turn signals which are safer and more efficient when roads are saturated, but which are annoying when traffic is sparse. My suggestion of the flashing red arrow would serve as a compromise between the "five-light" signal and the annoying "left turn on green arrow only" signals.
||[substantially rewrote annotation 14-Feb]
||If there is no-one around ... "No cop, no stop." Thats from Southern California btw...
||<<Additionally, a motorist expecting to
turn left is allowed to enter the
intersection before the way is clear for
him to proceed, provided he does not
actually enter or cross the on-coming
lane until it is safe to do so.>>
||In Oregon, it is common for people to
do this - nudge out into intersection
waiting for a turn, then zip across when
the oncoming traffic finally stops,
passing through the intersection on the
red. Often, you can't get through the
intersection otherwise - one car per
light cycle gets through, on the red. A
dedicated turn lane is badly needed for
some of these, and your solution would
||The intersection I must travel through
near my house is that way - we get at
least one major accident a week from
people trying to get across at the end of
the yellow and getting t-boned by
someone who runs the yellow. (To make
matters worse, there are train tracks a
block up on the other side of the
intersection, and if there's a train there,
you won't ever get a green even to turn
left - I've been stuck there for half an
hour before when there was someone in
front of me waiting to go straight and
the stupid train was stopped, and run it
several times when I was first in the left
||In any case, what I wanted to point out
that if you nudge out and wait, and then
zip across as the light turns, you CAN
be sited for running the red light - in
Oregon anyway, and the cop told me it's
the same in California. Basically, by the
law you ought not to enter the
intersection until it is safe for you to
leave it. Of course this is completely
impractical, but I have a warning ticket
to prove that some police do care.
||// In any case, what I wanted to point out that if you nudge out and wait, and then zip across as the light turns, you CAN be sited for running the red light - in Oregon anyway, and the cop told me it's the same in California. Basically, by the law you ought not to enter the intersection until it is safe for you to leave it. Of course this is completely impractical, but I have a warning ticket to prove that some police do care.//
||If one is not allowed to enter an intersection to make a left turn until one can be assured of being able to complete the maneuver immediately, then many intersections without turn arrows will become completely impassible during much of the day.
||I'll confess to some bewilderment as to why nobody likes this idea, since it would seem a useful compromise between a 'five-light' signal and the annoying 'left turn on green arrow only' ones.
||BTW, it would also have a safety advantage over the five-light signals: if the left-turn-lane sensor feeding a five-light signal doesn't register a vehicle, a motorist in the lane may not notice that when the light changed he didn't get the green ARROW and thus should not immediately proceed. If the signal changed to a flashing red arrow, he would recognize that he could proceed if there were no on-coming vehicles, but not otherwise.
||//You are correct, it would be useful. It wouldn't apply in some situations, such as where the intersection is just prior to the crest of a hill. There may be liability implications to look into. I like it. [+]//
||Thanks. Glad to see the idea's getting some approval. As I said, I see it as a **COMPROMISE** for situations where a five-light signal would not be adequate for reasons of either safety or main traffic flow (such intersections often have stragglers in the left-turn lanes; if there is considerable imbalance in the number of motorists wanting to turn left from the N/S and E/W roads, such stragglers improve left-turn throughput; if left-turn lanes are crowded in both directions they worsen throughput all around).
||It seems to me that at 12:30am when there's no other traffic around, it's silly to have to wait over a minute to get an arrow to turn left, when it could be done *SAFELY* at any time. A flashing red arrow would allow for this very nicely.