Ada County Highway District

ACHD's Road Wizard Sunday, July 16, 2017 ACHD's Road Wizard

The point of green road stripes at the Main Street/Fairview Avenue/Garden Street intersection; the benefits of green left-turn-arrow signals coming after through-traffic green; view of oncoming traffic turning left from Laramie Place onto Eastgate Drive meets requirements but speeding is a problem

The Road Wizard Replies

Dear Road Wizard: What do green road stripes mean, such as those at the very west end of Main Street going up to Fairview Avenue in Boise?


Road Wizard:

The markings on Main at Garden Street look like a green crosswalk, but they aren't meant for foot traffic.

The route from Main to Fairview briefly parallels the Interstate 184 Connector and may not be a good situation for more tentative bicyclists, but there is a nice bike lane. Bike lanes don't typically continue through intersections, but Main/Fairview/Garden is particularly tricky.

There are many right-turning drivers at two different, close-together right turns. The green paint through the intersection is a guideline for bicyclists and lets drivers know that there are potential conflicts between motorized vehicles and bicycle traffic.

Dear Road Wizard: How does ACHD determine if a green left-turn signal is before or after the regular green? I would think where few people turn left that the left-turn signal would be after the through-traffic green as those few people could turn on the flashing yellow, thereby obviating the need for a left-turn signal and improving traffic flow. This doesn't seem to be the case.


Road Wizard:

There are many signal locations where left-turn arrows come after the through green light. It's known as a "lagging left."

A lagging left can be used just as Mark describes. Drivers can first attempt to make the left turn at a flashing yellow arrow while through traffic has a green light. If all of the left-turning drivers are able to turn during the yellow arrow, the protected green arrow, which stops through traffic, isn't displayed. Signals at Broadway Avenue and University Drive, Five Mile Road and Executive Drive, and Franklin Road and Main Street in Meridian are some of the locations that have this setup.

Lagging lefts are also used where left-turn lanes commonly fill up with waiting vehicles. This prevents drivers in the left-turn lanes from backing up far enough to block through traffic.

Dear Road Wizard: I live on Laramie Place in the Oregon Trails neighborhood. When exiting from Laramie, making a left, it's impossible to have a line of sight for the oncoming traffic unless I creep out part way onto Eastgate Drive. Eastgate curves, plus the residence on the corner had plantings that blocked the view. In addition, although the speed limit is 20 mph, very few drivers obey that. As a result I have come close to being hit several times, twice this past week. What can ACHD do to ease this situation?


Road Wizard:

An ACHD traffic engineer visited this residential intersection to have a peek. There is a required sight distance at street crossings, and at Laramie and Eastgate, the view of oncoming traffic exiting Laramie barely met requirements for the posted speed limit. But Robin is correct, speeding is common.

What ACHD can do in these cases is contact homeowners about cutting back shrubbery. Parking can also be restricted if it blocks the view. Those aren't contributing factors here, however.

The curve of the road limits the sight distance more than anything else. As for the speeding, ACHD has already installed speed bumps and posted speed limit signs. ACHD can't enforce speed laws, so it may be time for residents to contact police about the problem, if they haven't already.

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