Ada County Highway District

Ten Mile Road and Amity Road Roundabout

General Description:

Project Background

The Ten Mile and Amity roundabout project is an outcome of recommendations from the Ada County Roundabout Study: Amity Road Intersections. As part of the study, six intersections along the Amity Road Corridor were evaluated to determine whether a roundabout would be an appropriate traffic control measure to accommodate future growth.

The Ten Mile Road and Amity Road intersection was one of four intersections determined as viable for a future roundabout because:

  • The Amity Road corridor is frequently used as a parallel access to Interstate 84
  • A roundabout will increase traffic flow and improve safety
  • It is in close proximity to the Idaho Transportation Department's future Ten Mile Interchange (currently scheduled for construction in 2009/2010)
  • A roundabout will accommodate projected growth in the area

Project Description

  • Build a single lane roundabout with the option for expansion to 2 lanes in the future when traffic volumes warrant it
  • 12-14 foot travel lanes
  • 5-foot gravel shoulder
  • 20 mph advisory speed limit through roundabout
  • Large trucks/vehicles may use 'truck apron' around perimeter of roundabout if needed
  • Center portion of roundabout will include colored, patterned concrete

In June 2007, ACHD held a public open house to share the roundabout study information and conceptual plans for a roundabout at Ten Mile and Amity. ACHD Commissioners adopted the recommendations from the Ada County Roundabout Study: Amity Road Intersections in January 2008. Since then, a preliminary roundabout design has been created and was presented for public input at an open house in March 2009. To view open house displays, which include the preliminary design or to comment on the project, see "Related Documents" located on the upper right side of this page.


Questions and Answers


Q: How will the proposed roundabout improve


Over time, the current 2-way stop-controlled intersection will not be able to accommodate anticipated traffic growth and function safely.

A roundabout will help to:

Ease congestion.

Motorists yield to vehicles in the circulating roadway, helping to decrease congestion and backups.

Slow vehicle speeds.

The design of the roundabout will require motorists to slow to 15 - 20 mph as they enter and use the roundabout. This also makes it safer for bicyclists, as vehicles and bikes would be traveling at similar speeds.

Reduce accidents at intersections.

Slower speeds and fewer conflict points than a traditional intersection lend to making a roundabout safer.Studies have shown that roundabouts can significantly reduce most right-angle and head-on collisions that can occur at an intersection.


Q: Why are sidewalks not included in the project?


Because of the current rural nature of the Ten Mile and Amity area and lack of current sidewalk connectivity, sidewalks are not part of the preliminary roundabout design. American's with Disabilities Act (ADA) requires that when building sidewalks all pedestrian improvements be made -- this would include ramps, refuge islands and the sidewalk itself. These pedestrian improvements could require signifi cant modifi cation when the roundabout expands to two lanes in the future. Instead, sidewalks will be built as development in the area warrants them and allows for connectivity.  


Q: When will the roundabout be constructed?


Based on the currently adopted 2009-2013 Five-Year Work Plan (ACHD's five year project planning document), the purchase of right-of-way is planned for 2010 and construction is programmed for 2011. These years are subject to change based on the ACHD Commission's adoption of the 2010-2014 Five-Year Work Plan.


Time Frame

Start Date:
Construction 2014
End Date:

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