US-20 Ashton to SH-87 JC

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With growth in traffic and tourism, it is time for ITD to find a solution to address safety and capacity concerns on US-20 between Ashton and the junction with SH-87. ITD must find a solution that will handle increased traffic, meet driver expectations, and improve safety.

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Increasing congestion is contributing to traffic crashes in the area.

Here’s what the traffic data says:

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Since 2021, ITD and the Federal Highway Administration (FHWA) have been working with the public, elected officials and agencies to look at options for improvement safety and reducing congestion on US-20.

ITD anticipates incorporating recommendations made as part of this planning study into future NEPA studies, per Title 23 of the US Code, Part 168.

For more information, view the Level 1, Level 2, Level 3a, and Multi-Use Crossing maps. If asked to sign in, please hit cancel and you will be entered into the site.

Screening consists of evaluating each alternative against set criteria such as:

1. Access Management
2. Environmental Resources
3. Constructability
4. Mobility
5. Traffic Operations
6. Safety

Alternatives that don't meet the criteria or have fatal flaws are eliminated. Alternatives needing refinement are modified to reflect stakeholder and agency suggestions or regulatory requirements.

What are Alternating Passing Lanes, or Two Plus One Highway?

An alternating passing lane or two plus one highway has alternating passing lanes added to a two-lane highway to allow drivers to pass slower vehicles. The passing lane alternates from one direction of travel to the other within a section of roadway allowing passing opportunities in both directions. A two plus one project can be introduced on an existing two-lane roadway where there is a significant amount of slow moving traffic, limited sight distance for passing, and/or traffic congestion that could be alleviated if motorists had the ability to pass slower vehicles on a more frequent basis.

Alternating Passing Lanes has several challenges including increased close calls and crashes at transition points.

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Design Alternatives

Challenges: Head-on perception

Challenges: Crown location for snowplows, keeping slower traffic to the right, merging left

Passing Lane Attributes

1.5–2.0 Mile Preferred

Note: Driveway access and approach integration in this configuration is based on IDAPA Standards.

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At-Grade Intersection

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Beneftis

• The wider median gives drivers a refuge so they can wait to turn safely
• Provides space to accelerate and decelerate
• Separates turning and through traffic

Challenges:

• Potentially increases the possibility of intersection crashes

For a more detailed look, view the At-Grade Intersection video

Alternating Passing Lane Intersection without acceleration or deceleration lanes

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Beneftis

• Allows for designated left-turn lanes on highway

Challenges:

• Through traffic is reduced to a single lane in each direction at intersections
Adding right-turning lanes would require wider highway
• Passing lanes must merge lanes before reaching the intersection

ITD is evaluating:

• Multi-use crossing opportunities at trails, pathways, and bridge locations that intersect US-20
• Cyclists
• Pedestrians
• Snowmobilers
• ATV/UTV riders
• Equestrians
• Snowshoers
• Fishermen and other sportsmen
• Hikers and other trail users
• Wildlife crossing infrastructure
• ITD is evaluating movement and wildlife migration information. Technical assistance is being provided by the U.S. Forest Service, U.S. Fish and Wildlife Service, and Idaho Fish and Game.

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Purpose

The purpose of the US-20 Ashton to SH-87 Junction project is to enhance highway safety and operations by:

• Decreasing crash severity
• Addressing traffic growth in the corridor
• Improving access management
• Addressing regional freight movement

Need

The need for improvements to the US-20 corridor is to:

• Address existing deficiencies, such as:
• Safety
• Travel time
• Congestion
• Delays
• Prepare for future growth, economic development and tourism in the region
• Increase freight mobility

Goal

When consulting with the public and resource agencies, ITD identified additional goals to be considered as the project is developed:

• Provide traffic calming measures or separation where the US-20 alignment runs through developed areas
• Provide multiuse solutions that provide a range of options for recreational users
• Integrate wildlife movement strategies in the corridor

Alternatives will be evaluated through a screening process to determine how well they meet the project’s draft purpose and need. The screening process includes evaluating each alternative based on the following 11 environmental criteria.

1. Visual Resources
2. Agricultural and Forest Resources
3. Air Quality
4. Biological Resources
5. Cultural Resources
6. Geology and Soils
7. Hazards and Hazardous Materials
8. Hydrology and Water Quality
9. Land use and Transportation Planning
10. Noise
11. Social and Economic Resources