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Environmental Review Toolkit


Idaho Transportation Department: Corridor Planning/NEPA Integration Guide

Planning and Environment Linkages: State DOT Institutional Mechanisms

Corridor planning began in Idaho as an effort to improve the planning process, and is now the primary method for conducting medium and long-range planning on state system corridors. Early on, planners encountered issues regarding the relationship between the corridor planning process and project selection and development. They identified a need for guidance on integrating NEPA into the corridor planning practices, which led to the development of the Corridor Planning/NEPA Integration Guide. The integration guide describes a range of options for NEPA involvement within corridor planning through scoping, project and cumulative assessments, and alternatives analysis, including documentation of alternatives considered.


In Idaho, corridor planning is the primary method for conducting medium and long-range planning on state system corridors. While there is a State Long Range Plan (LRP), it is more of a visionary document that functions as a policy plan rather than as a way to identify recommended improvements in specific corridors.

Corridor planning began in Idaho through an internal movement to improve the planning process. This process began with FHWA concurrence. The Idaho Transportation Department (ITD) developed the Idaho Corridor Planning Guidebook before they attempted corridor planning. At the time, corridor planning was new to Idaho, but neighboring Oregon had experience in corridor planning and Idaho looked to their process for guidance.

The Idaho Corridor Planning Guidebook (available at was approved by the Idaho Transportation Board in February, 1998, and was most recently updated in December, 2006. The introduction to the Guidebook begins with several key concepts, including:

  • Corridor planning will assist prioritizing transportation projects and preserving public right of way.
  • Corridor planning can comprehensively address future transportation needs and develop management strategies in the corridor area.
  • Corridor planning is supported by land-use and transportation-related policies and statutes at both the state and federal levels
  • The same key elements, tailored to the specific corridor, will be featured in all Idaho Corridor Plans.
  • Corridor planning fosters cooperative state and local transportation planning efforts and the development of context sensitive solutions.
  • All corridor planning activities require a statement of purpose and need.
  • Active public participation is an essential element of the corridor planning process.
  • Multimodal transportation concepts will be considered.

While there are not currently corridor plans on every corridor in the state, the practice is moving in that direction.

Need for NEPA Integration with Corridor Planning

Early in Idaho’s corridor planning experience, planners encountered issues regarding the relationship between the corridor planning process and project selection and development. The corridor planning process involves analysis and evaluation of potential improvements within the study area, based on public involvement, district priorities, cost, and an environmental scan. These steps all help to identify potential environmental problems or implementation difficulties that may be encountered as proposed projects proceed into the more formal project development process.

The first corridor plan in Idaho was for U.S. 20 from Idaho Falls to Ashton (this is a major route to Yellowstone National Park). The corridor planning process included extensive public involvement and analysis and subsequent selection and elimination of various potential improvements. Confusion arose regarding the necessary NEPA documentation when the improvements were moved forward to the project development process. After completing the corridor plan, there was some question of whether potential improvements could be eliminated based on public participation in the corridor planning process, or if they could be eliminated only through a formal NEPA process. ITD planners were concerned that they might have to re-open some of the work that had already been completed, and were also concerned that the public would be confused and distrustful if alternatives they considered to be eliminated were now available again for further consideration.

The experience with the U.S. 20 corridor plan led to the development of guidance for the integration of NEPA and Corridor Planning practices, with information on the appropriate level of coordination required, given the possible future construction of projects developed through the corridor planning process.

Development of the Integration Guide

In 2004 the “Idaho Corridor Planning and National Environmental Policy Act Integration Guide” was finalized. The writing of the guide was a collaborative effort, including two ITD Senior Planners, the ITD Environmental Manager, and the FHWA Idaho Division Transportation Planning Engineer. The integration guide describes a range of options for NEPA involvement within corridor planning through scoping, project and cumulative assessments, and alternatives analysis, including documentation of alternatives considered (see Corridor Planning/NEPA Decision Matrix). There are a number of procedural options for local agency and district office consideration and application.

The Integration Guide suggests that an Interagency Advisory and Assessment Team (IAAT) be formed for currently identified and future State Highway System (or local) corridors for which a corridor plan is being contemplated. The IAAT members include: ITD district personnel (Sr. Transportation Planner, Sr. Environmental Planner, Project Development staff, etc.) and appropriate resource and local agency representatives. It may also include the FHWA transportation planner or engineer as well as representatives from the local highway technical assistance council (represents all local highway district and local governments).

In Idaho, corridor planning is managed by one of the six Idaho Transportation Department (ITD) district offices. The District Senior Transportation Planner is typically the corridor planning lead, with the IAAT providing advice and input as needed. Early involvement and issue identification helps to determine the final makeup of a particular IAAT.

Planning since Release of the Integration Guide

Corridor planning is conducted at the district level and the degree of NEPA integration is at the discretion of the district. Some districts are very interested in doing corridor planning and appreciate the additional guidance to improve the process. Other districts, however, have been slower to accept corridor planning and some may not do it at all, due to the unavailability of funds to implement major expansion projects that may be identified through the corridor planning process.

Since the Integration Guide was completed, roughly half a dozen corridor plans have been completed that followed all of the steps in the process. While the entire process is not followed for every plan because it may be clear from the outset what level of environmental analysis is needed, it is typically followed more closely in areas with environmental issues of greater sensitivity. Pre-planning meetings do take place and include resource agencies earlier in the process, but it may occur on a more informal basis. The Integration Guide describes multiple levels at which environmental decisions can be made. The majority of the corridor plans do not include an entire NEPA process, but they do at least include an environmental scan and consider important environmental issues much earlier in the planning process.

One benefit of integrating the corridor planning and NEPA processes is that it provides ITD a more structured approach to considering how to evaluate corridors and projects. For example, there are several corridors where ITD would like to obtain right of way (ROW) to preserve for future projects.

The corridor planning/NEPA integration process and Corridor Planning Guidebook have helped ITD Districts frame the issues and consider how to approach corridors. The options include:

  1. Conduct a corridor study of the entire corridor followed by NEPA evaluations of the identified individual projects;
  2. Conduct a NEPA evaluation of the entire corridor (skip the corridor study altogether);
  3. Conduct a combination of 1 and 2 (a corridor study combined with NEPA evaluations of known projects); or
  4. Conduct a tiered NEPA EIS (with Tier 1 effectively serving as the corridor study and having full NEPA standing).

The Districts typically select one of the first two options. While the same decision could be reached without the process and guide, the decision likely would not give as much consideration to the other possible approaches.

Improvements to the process

One improvement to the planning process is that now, user needs identified in the process are documented in a database, categorized and assigned to a logical system (signs, signals, right of way, pavement, planning, etc.) and tracked until met or found to no longer be needed. This improves overall documentation and ensures that important issues are not forgotten.

Also, ITD has found that for corridor plans on lower-volume, typically rural two-lane facilities, it has not been efficient to perform the level of planning outlined in the Corridor Planning Guidebook. They developed guidelines for lower volume facilities that involve less public involvement and a more limited environmental scan. This improved process has saved considerable time and effort.


ITD has found that the integration of the corridor planning and NEPA process tends to lead to a smoother project development process in some cases. In ITD District 6, the corridor planning manager is taking corridor planning and NEPA integration to a higher level. The senior planner and the environmental manager work side by side with resource agencies to implement the plans and manage the projects.

Lessons Learned

In general, the early involvement with resource agencies and the public has been quite positive, with the many stakeholders appreciating the early contact and solicitation. One success was a project in which stakeholders and the IAAT identified a culvert on Targhee Creek that impeded Yellowstone Cutthroat Trout from returning to their natural spawning habitat from Henry’s Lake. From a purely transportation engineering perspective, it would have been acceptable to leave the culvert in place for several years until it needed replacement, but it was very important to the public to protect the natural system and prevent Henry’s Lake from losing its Yellowstone Cutthroat Trout population. Eventually, the collaborative process led ITD to replace the culvert with a bridge and return Targhee Creek to a natural flow. This effort, which won an Environmental Excellence award from the American Association of State Highway and Transportation Officials (AASHTO), came about initially because of the corridor planning process and the NEPA/Corridor Planning Integration IAAT.


One challenge in Idaho has been the lack of consistency between districts in conducting corridor planning in general, and specifically in using the corridor planning /NEPA integration process. While local autonomy is very useful in some ways, the integration efforts could benefit from more collaboration, education, and standards within ITD’s environmental units and resource agencies. It should be noted, however, that the Corridor Planning Guidebook and corridor planning /NEPA integration process are guidance, not procedural manuals.

There was no dedicated funding for corridor planning (and therefore the Planning/NEPA integration process when needed) until somewhat recently, and some ITD Districts were reluctant to take funds from the construction budget to prepare corridor plans. While a proactive planning process should theoretically save money in the long run, it was often a challenge to decide to dedicate scarce funds. A former ITD Director who was supportive of corridor planning set aside dedicated funds for corridor planning about three years ago, but the funds may not be available after 2009 under current federal and state revenue projections. It is unclear what the future of corridor planning and integration efforts will be without dedicated funding, although it remains current policy.

Another issue is that if a NEPA document is prepared for an entire corridor (Approach One in the Corridor Planning/NEPA Integration Guide) which identifies multiple improvements in the corridor and ITD is not able to begin the projects within a certain timeframe (usually 3 years), the NEPA portion of the document may be considered out of date and the work would need to be re-evaluated during project development process.

Another challenge is staff turnover and retirement. None of the senior planners currently in the district offices were there 10 years ago when ITD started doing corridor plans, and few of the current senior planners have much corridor planning experience.

Next Steps

Several years ago FHWA conducted a “Linking Planning and NEPA” course in Idaho that concentrated primarily on the corridor planning process as the primary method for planning/NEPA integration to occur. There is some feeling that while the workshop was very useful, additional levels of cooperation may be needed between transportation and resource agencies. There will be a series of meetings beginning in September, 2008, with environmental planners from across the state to talk about integrating planning and NEPA.

For more information, contact:

Ronald K. Kerr
Senior Transportation Planner
Rail and Intermodal, Idaho Transportation Department
Phone: 208.334.8210