Ada County Highway District

ACHD's Road Wizard Sunday, June 9, 2019 ACHD's Road Wizard

How about policy and signage for zipper merges? Bike lane project closes bike lane at Protest/Kootenai/Federal Way

The Road Wizard Replies

Dear Road Wizard: I saw an article in the news about zipper merges. It said the Idaho Transportation Department wants motorists to use this method, and a search of your columns also revealed a discussion of this in May 2015 which you promote this method. I totally agree that this method is safer, more efficient, and would prevent many incidents. I have, however, never seen a sign in Idaho warning there is a zipper merge ahead, either permanent or temporary, as would be necessary to warn motorists to use both lanes to a specific merge point. I checked the Idaho Driver's Manual and it says nothing about a zipper merge. So until these signs are in place, as well as a policy for handling a zipper merge, most motorists will treat a merge as if the ending lane must yield to the continuing lane, which is what I was taught in driver training many years ago. Thank you for your very informative column!


Road Wizard:

The question in 2015 was about the abundant "two thru lane" intersections that merge down to one lane past signalized intersections. The column also mentioned the tendency of Idaho drivers to plan well ahead of a merge and hold fast to their place in line, rather than alternating turns at the merge point. This can cause longer backups relative to what is considered a smoother, zipper merge approach.

There is also the matter of driver patience/impatience. Sometimes patient drivers in the continuing lane will be passed by fast-moving, impatient drivers who "take cuts." In these cases, the better approach is for drivers in the continuing lane to leave gaps for merging traffic while maintaining a steady speed. People in the ending lane should look for those gaps and try to merge at about the same speed as traffic in the continuing lane.

But zipper merges tend to be more appropriate for interstate projects, which relates more to the Idaho Transportation Department's jurisdiction. Multilane arterials, such as those managed by ACHD, have driveways and side street access points that complicates zipper merging.

ITD is in the best position to motivate drivers to zipper merge, but widespread implementation will take some getting used to. Signs and education could help with this aspect of driver behavior.

Dear Road Wizard: Why isn't there a bike detour in place for the road closure at Protest/Kootenai/Federal Way? I got to the top of Protest and saw the small "Bike Lane Closed" sign, but no detour information for cyclists on how to get to Columbus. What gives?


Road Wizard:

ACHD often posts bike lane closures and detours with major projects. They tend to be employed in cases where there is a continuous bike lane, and where it's not reasonable to expect a bicyclist to share the road with traffic in the construction zone.

But in this case, the bike lane coming up the hill on Protest actually ends at the railroad tracks just west of Federal Way, and bicyclists normally have to merge alongside traffic, construction or not. That is why a detour was not posted specifically for bicyclists.

The irony is that this project actually involves constructing a new bike lane which will continue farther west on Kootenai Street. Bicyclists can use wider Overland Road as an alternative route to Columbus. Overland doesn't have bike lanes, but work to add bike lanes is underway.

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