Ada County Highway District

ACHD's Road Wizard Sunday, February 25, 2018 ACHD's Road Wizard

Resident on Boise Avenue between Apple Street and Law Avenue request signs cautioning pedestrians and Bicyclists about cars backing out of driveways; reasons why the through lane on Silverstone Way at Overland Road shouldn't also be a left-turn lane.

The Road Wizard Replies

Dear Road Wizard: Please address the need for signage on Boise Avenue between Apple Street and Law Avenue regarding caution about cars backing out of driveways. There has been an exponential increase in traffic as Boise Avenue is now a main thoroughfare between new developments in Harris Ranch, Surprise Valley, etc. I have witnessed innumerable close calls backing slowly out of my driveway with a blind spot due to fencing in another yard. Foot traffic and bicyclists assume they have free clearance and never think or look for a vehicle that may be pulling out. Also students walk this street every day to and from Timberline High School.


Road Wizard:

Traffic on Boise Avenue has actually decreased over the years. In 1996, the average daily number of vehicles was around 11,500. In 2015, it was about 8,400.

Parkcenter Boulevard, with the construction of the East Parkcenter Bridge in 2010, is a better route for many people. Boise Avenue takes drivers through the busy intersections of Broadway Avenue and University Drive/Capitol Boulevard to get to downtown Boise.

But Boise Avenue is still busy and there are many driveways between Apple and Law. There are also sidewalks and bike lanes, and a 30 mph speed limit.

Motorists must always yield to bicyclists and pedestrians. Pedestrians and bicyclists also need to be aware of what is happening around them, and the potential for the view of vehicles to be blocked by landscaping or fences. ACHD doesn't have jurisdiction over private driveway sight obstructions.

There are "hidden driveway" signs that are used in rural areas where speeds are higher and driveways are few and far between. That doesn't apply to Boise Avenue.

Dear Road Wizard: When going north on Silverstone Way, the light at Overland Road has the middle lane set up to go straight. No one goes that way; all the traffic turns left and backs up at rush hour. Why not make the middle lane a straight and left turn?


Road Wizard:

Silverstone to the north was a developer-driven project and this fourth "leg" of the intersection went into operation in December 2017.

Attention is already given to the backed-up northbound left-turn lane. Both northbound and southbound traffic have protected green arrow and flashing yellow arrow left-turn signals. When there is only a car or two heading south, northbound left-turning traffic gets extra green arrow time.

Because Silverstone is a side street off of Overland, both northbound and southbound Silverstone traffic need to be moving through the intersection at the same time in one way or another. That way Silverstone takes minimal green time from busy Overland.

Adding a through/left-turn lane to the existing arrangement wouldn't be the most efficient way to time the traffic signals, and would also not be safe. For example, left-turning southbound drivers wouldn't know if motorists in the shared northbound lane were going straight or turning left. This would impact the safety of southbound drivers attempting to turn left during breaks in oncoming traffic.

To safely have a shared lane for northbound Silverstone, all southbound traffic would have to be stopped at red lights. This type of taking turns would require longer green light time for Silverstone, time that could only come from Overland traffic, and doing that would cause worse delays than it would solve.

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