Leading vs. Trailing green arrow at traffic intersections

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Sirrip
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Joined: Sun Jun 20, 2010 7:54 pm

Leading vs. Trailing green arrow at traffic intersections

Post by Sirrip »

Anyone here have a good idea as to why some cities have a leading green left arrow, and some have a trailing green left arrow at traffic intersections? It seems to me that the throughput would be the exact same. Why is there no universal standard? Only thing I can think of is that it must be a safety issue.
555
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Joined: Thu Dec 24, 2009 6:21 am

Post by 555 »

Presumably it is to do with optimizing traffic flow.

One design problem they have is when you want to turn right on a red light, there is usually nothing to indicate whether the oncoming traffic has a green turn left arrow (so they are entering the same road as you) so you don't know who has priority.
epilnk
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Joined: Wed Apr 18, 2007 7:05 pm

Re: Leading vs. Trailing green arrow at traffic intersection

Post by epilnk »

Sirrip wrote:Anyone here have a good idea as to why some cities have a leading green left arrow, and some have a trailing green left arrow at traffic intersections? It seems to me that the throughput would be the exact same. Why is there no universal standard? Only thing I can think of is that it must be a safety issue.
A trailing arrow is preferred if the left turn lane is short, especially when there is a physical barrier such as a bumped out median. Otherwise left turning vehicles get stuck in line behind cars going straight and are unable to reach the turn position until too late.
livesoft
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Post by livesoft »

Trailing green arrows are a good way for left-turning folks to be broad-sided by oncoming folks running the red light. With leading green arrows, the oncoming traffic has been sitting stopped waiting for the cross traffic.

With significant left-turning traffic, a 4-way intersection, might have each way go separated for a sequence of 4 light groups.
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strafe
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Post by strafe »

livesoft wrote:Trailing green arrows are a good way for left-turning folks to be broad-sided by oncoming folks running the red light. With leading green arrows, the oncoming traffic has been sitting stopped waiting for the cross traffic.

With significant left-turning traffic, a 4-way intersection, might have each way go separated for a sequence of 4 light groups.
Leading green arrows are a good way for left turning folks to be broadsided by traffic running the red light on the cross street, which are harder to see and avoid.
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