Ada County Highway District

ACHD's Road Wizard Sunday, January 21, 2018 ACHD's Road Wizard

Request for a pedestrian crossing on River Valley Street to the Boise Co-op at the Village at Meridian; surprised reaction to the continued closure of the second left-turn lane on northbound Ten Mile Road at Franklin Road.

The Road Wizard Replies

Dear Road Wizard: I am requesting a pedestrian crossing on River Valley Street to the Boise Co-op at The Village at Meridian. Residents have to cautiously cross four lanes to get across the street. It seems absurd why a crossing of some kind was not initially put in when that whole area was completed.


Road Wizard:

This section of River Valley Street has a 25 mph speed limit, and the four lanes include a shared center turn lane.

A crosswalk wasn't installed originally for several reasons. First, this isn't an intersection of two public streets.  River Valley is a public road, but the Boise Co-op shopping area entrance is a private driveway. So is the entrance to the apartments across the street.

And second, even with so many apartments along River Valley, it was hard to determine in the planning process if there would be that many residents crossing at the particular location by the Boise Co-op. Plus, it was apparent that motorized traffic volumes would be relatively low at first.

This is important to consider because adding a crosswalk can include more than just street paint and signs. Pedestrian-activated crossing beacons may be needed, as well as sidewalk ramps.

One such crossing was installed on the other side of the Boise Co-op shopping complex on Village Drive after ACHD observed heavy crossing activity there due to shoppers parking across the street from their destinations.

River Valley doesn't have the same parking-and-crossing situation. But ACHD will look at current pedestrian demand, as well as the number of passing vehicles and traffic gaps, to determine if a crosswalk is justified at this time.

Dear Road Wizard: When I read your recent response to delaying the opening of the second left-turn lane on northbound Ten Mile Road at Franklin Road, I was surprised. With the installation of the second lane, twice the number of vehicles could safely turn left, 24/7. Why wait until even more cars line up? Turning left on a blinking yellow arrow is dicey at best. Maybe someone might want to look at this one again.


Road Wizard:

On paper it would seem to make sense to open a second left-turn lane, double the turning capacity. But when a flashing yellow left-turn arrow is part of the equation, the numbers don't add up that way.

Northbound Ten Mile has about twice as much traffic as southbound Ten Mile during the evening commute. As a result, drivers turning left from northbound Ten Mile onto Franklin get a lot of extra time to turn left while the flashing yellow arrow is displayed. That's because the lighter southbound traffic provides plenty of opportunities to turn. Additionally, southbound Ten Mile traffic has a speed limit of 40, which is an appropriate speed for installing flashing yellow arrows.

Flashing yellow arrows are not used in dual left-turn lanes because a driver in one lane may obstruct the view of oncoming traffic for a driver in the other lane. Opening both lanes and only allowing "protected" left turns during a green arrow signal would increase turning capacity only by about 20 percent during the evening commute. And it would increase delays overall for left-turning drivers throughout the day.

ACHD is already planning on looking at the traffic signal again in the coming weeks, but for now the lane remains closed.

Return to Road Wizard

Have a Question for the Wizard?

E-mail it to:

Or mail it to:
Road Wizard
3775 Adams St.
Garden City, ID 83714

You may include photos of a particular situation, but photos cannot be returned.

Road Wizard Archives

Additional years are also available by request.


We Drive Quality Transportation For All Ada County ~

Ada County Highway District © 2017
For Questions or problems with this Web site contact the Webmaster