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Island Park US 20 Island Park U.S. 20 Targhee Pass Environmental Assessment Junction S.H. 87 to the Montana State Line U.S. Department of Transportation Federal Highway Administration and the Idaho Transportation Department Project Key 14054 and 19913 December 2018 Persons with disabilities may request this information be prepared and supplied in alternate forms by calling the Idaho Transportation Department (ITD) District Environmental Office at 208-745-5602 or ITD Headquarters Environmental Office at 208-343-8842. ITD hereby gives public notice that it is the policy of the department to assure full compliance with Title VI of the Civil Rights Act of 1964, the Civil Rights Restoration Act of 1987, Executive Order 12898, and the related statutes and regulations in all programs and activities. Title VI requires that no person in the United States of America shall, on the grounds of race, color, sex, national origin, or low income, be excluded from participation in, be denied the benefits of, or be otherwise subjected to discrimination under any program or activity for which ITD receives federal financial assistance. (this page is intentionally blank) Contents 1 Purpose and Need ................................................................................................................................. 1 1.1 Project Background ....................................................................................................................... 1 1.2 Project Purpose ............................................................................................................................. 1 1.3 Project Needs ................................................................................................................................ 1 1.3.1 Roadway Structure ................................................................................................................ 3 1.3.2 Traffic Flow .......................................................................................................................... 3 1.3.3 Safety .................................................................................................................................... 5 1.4 Scoping ......................................................................................................................................... 7 1.4.1 Additional Project Goals and Objectives .............................................................................. 7 1.4.2 Impact Analysis Topics ......................................................................................................... 8 2 Alternatives ......................................................................................................................................... 11 2.1 Road Improvements Common to Build Alternatives .................................................................. 11 2.1.1 Road Widening and Hill Cut ............................................................................................... 11 2.1.2 Turn Lanes .......................................................................................................................... 11 2.1.3 Shade Reduction ................................................................................................................. 16 2.1.4 Improved Road Base, Drainage, and Pavement Resurfacing .............................................. 16 2.2 Ability to Meet Project Needs ..................................................................................................... 16 2.2.1 Roadway Structural Deficiencies ........................................................................................ 16 2.2.2 Traffic Flow ........................................................................................................................ 17 2.2.3 Safety .................................................................................................................................. 18 2.2.4 Additional Project Objectives ............................................................................................. 18 2.3 Alternatives Advanced for Detailed Analysis ............................................................................. 19 2.3.1 Alternative 1: No-Build ...................................................................................................... 19 2.3.2 Alternative 2: Wildlife Crossing Structures and Fence ....................................................... 20 2.3.3 Alternative 3: Animal-Detection System ............................................................................ 23 2.3.4 Alternative 4: One Wildlife Crossing Structure and At-grade Wildlife Crosswalks .......... 25 2.3.5 Alternative 5: Operational Wildlife-Vehicle Collision Reduction Strategies ..................... 26 2.4 Alternatives Considered but not Advanced ................................................................................. 27 2.5 Alternatives Comparison ............................................................................................................. 29 2.6 Avoidance and Minimization Summary ..................................................................................... 36 2.7 Preferred Alternative ................................................................................................................... 38 3 Affected Environment and Environmental Consequences ................................................................. 39 3.1 Geologic Hazards and Soil Disturbance ..................................................................................... 39 3.1.1 Affected Environment ......................................................................................................... 39 i 3.1.2 Effects of the Alternatives related to Geologic Hazards and Soil Disturbance ................... 40 3.1.3 Avoidance, Minimization, and Necessary Permits ............................................................. 43 3.1.4 Cumulative Effects .............................................................................................................. 43 3.1.5 Conclusions regarding Geologic Hazards and Soil Disturbance ........................................ 43 3.2 Water Resources ......................................................................................................................... 44 3.2.1 Affected Environment ......................................................................................................... 44 3.2.2 Effects of the Alternatives on Water Resources ................................................................. 48 3.2.3 Avoidance, Minimization, and Necessary Permits ............................................................. 52 3.2.4 Cumulative Effects .............................................................................................................. 53 3.2.5 Conclusions regarding Impacts to Water Resources ........................................................... 53 3.3 Biological Resources................................................................................................................... 53 3.3.1 Affected Environment ......................................................................................................... 53 3.3.2 Effects of the Alternatives on Biological Resources ........................................................... 62 3.3.3 Avoidance, Minimization, and Necessary Permits ............................................................. 67 3.3.4 Cumulative Effects .............................................................................................................. 68 3.3.5 Conclusions regarding Impacts to Biological Resources .................................................... 69 3.4 Land Use and Transportation Planning ....................................................................................... 70 3.4.1 Affected Environment ......................................................................................................... 70 3.4.2 Effects of the Alternatives on Land Use and Transportation .............................................. 73 3.4.3 Avoidance, Minimization, and Necessary Permits ............................................................. 77 3.4.4 Cumulative Effects .............................................................................................................. 77 3.4.5 Conclusions regarding Land Use and Transportation Planning .......................................... 78 3.5 Traffic Noise ............................................................................................................................... 78 3.5.1 Affected Environment ......................................................................................................... 78 3.5.2 Effects of the Alternatives on Traffic Noise ....................................................................... 80 3.5.3 Noise Abatement Considered .............................................................................................. 81 3.5.4 Cumulative Effects .............................................................................................................. 82 3.5.5 Conclusions regarding Impacts of Traffic Noise ................................................................ 82 3.6 Visual Resources ......................................................................................................................... 83 3.6.1 Affected Environment ........................................................................................................
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