List of state highways in Idaho

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Highway names
InterstatesInterstate X (I-X)
US HighwaysU.S. Route X (US-X)
System links
  • Idaho State Highway System

The Idaho Transportation Department (ITD) is responsible for the establishment and classification of a state highway network, including 5,000 miles (8,000 km) of roads that are classified as Interstate Highways, U.S. Highways, and state highways within the state of Idaho in the United States.[1] The current state highway marker consists of a white background, black numbering, and a solid black geographic outline of the state of Idaho.


Marker design prior to 2020
Scenic state highway marker formerly used on Idaho State Highway 21

During the 1920s, in lieu of numbering its highways, Idaho had a system of lettered Sampson Trails.[2] They were marked by businessman Charles B. Sampson of Boise at no expense to the state, using orange-colored shields.[3] By 1929, the trails system had included 6,500 miles (10,500 km) of marked highways that covered most of the state.[4] By the mid-1930s, the state had adopted a more standard system of numbered state highways.[5][6]

In 1978, the ITD began using brown state highway markers to denote scenic Idaho highways,[7] in addition to the main highway markers that featured a black background and white lettering and the name "IDAHO" in black lettering inside a white geographic outline of the state. The brown markers were discontinued around 2012, and in April 2020, ITD changed the coloring of the main state highway marker to its current color scheme, also adding a wide version of the marker for three-digit highways and removing the word "IDAHO" from all markers in the process.[8]

Sampson Trails

Rand McNally Atlas from 1926 showing the Sampson Trails as well as US Highways

The following Sampson Trails were marked:[2]

State highways

Number Length (mi)[9] Length (km) Southern or western terminus Northern or eastern terminus Formed[10] Removed Notes
SH-1 12.279 19.761 US-95 near Copeland Hwy 21 at Porthill 01932-01-011932 current
SH-3 US-95 / US-195 (now US 2) in Ponderay MT 3 near Clark Fork 01929-01-011929 01940-01-011940 Replaced by US-10 Alternate
SH-3 117.680 189.388 US-12 near Spalding I-90 near Rose Lake 01953-01-011953 current
SH-4 7.380 11.877 I-90 in Wallace National Forest Road No. 7623 at Burke 01929-01-011929 current
SH-5 19.140 30.803 US-95 in Plummer SH-3 in Saint Maries 01929-01-011929 current
SH-6 40.645 65.412 SR 272 near Potlatch SH-3 near Santa 01929-01-011929 current
SH-7 16.563 26.656 Russell Ridge Road near Orofino Old Highway 7 in Ahsahka 01929-01-011929 current Formerly continued north to Harvard and south to Grangeville
SH-8 53.589 86.243 SR 270 in Moscow 1st Street in Elk River 01929-01-011929 current
SH-9 US-95 in Spalding S-412 at the Montana state line 01929-01-011929 01962-01-011962 Replaced by US-12
SH-9 13.522 21.762 SH-8 near Deary SH-6 near Harvard 01965-01-011965 current
SH-10 SH-7 in Greencreek SH-9 (now US 12) in Kamiah 01952-01-011952 01953-01-011953 Duplicated US 10; renumbered SH-62
SH-11 42.481 68.367 US-12 in Greer Forest Service Road No. 247 near Headquarters 01929-01-011929 current
SH-12 US-95 Business in Craigmont SH-62 in Kamiah 01929-01-011929 01962-01-011962 Renumbered SH-64 because US-12 extended into Idaho
SH-13 26.390 42.471 US-95 in Grangeville US-12 near Kooskia 01929-01-011929 current
SH-14 49.515 79.687 SH-13 near Harpster Airport Road in Elk City 01929-01-011929 current
SH-15 US-95 near Marsing US-30 in Boise 01929-01-011929 01967-01-011967 Renumbered as SH-55 (which continued west from Boise) because of I-15
SH-16 16.005 25.758 US-26 near Star SH-52 in Emmett 01929-01-011929 current
SH-17 SH-15 (now SH-55) in Banks Crouch 01929-01-011929 01960-01-011960 Now Banks-Lowman road; formerly continued east to Lowman; until 1938 continued east to Stanley;
SH-18 US-30 in Fruitland US-30 in Caldwell 01929-01-011929 01940-01-011940 Replaced by US-95 and US-20 (US-26 was added to this section of US-20 as a concurrency in 1952)
SH-18 Oregon state line US-95 in Parma 01953-01-011953 01975-01-011975 Now Wanstad Road and Roswell Road
SH-19 19.915 32.050 OR 201 near Homedale I-84 Business in Caldwell 01929-01-011929 current
SH-20 US-95 near Marsing US-30 near Nampa 01929-01-011929 01953-01-011953 Renumbered SH-72 because US-20 extended into Idaho; now part of SH-55; until 1939, continued southwest to Oregon state line
SH-21 130.869 210.613 I-84 in Boise SH-75 in Stanley 01929-01-011929 current
SH-22 43.936 70.708 SH-33 near Howe I-15 in Dubois 01929-01-011929 current Originally continued west to Mountain Home
SH-23 US-93 in Shoshone SH-22 in Carey 01929-01-011929 01941-01-011941 Replaced by US-93 Alternate (now US-93) and US-20 Temp (now US-26)
SH-23 US-93 (now SH-75) in Bellevue SH-68 (now US-20) in Picabo 01953-01-011953 01971-01-011971 Now Gannett Road; originally continued east to Carey
SH-24 67.533 108.684 I-84 / US-30 in Heyburn US-93 in Shoshone 01929-01-011929 current Originally continued west to Bliss
SH-25 58.048 93.419 I-84 near Jerome I-84 / SH-77 near Declo 01929-01-011929 current
SH-26 7.835 12.609 US-93 near Knull US-30 in Twin Falls 01929-01-011929 01953-01-011953 Renumbered SH-74 because US-26 extended into Idaho
SH-27 7.835 12.609 US-93 in Challis US-91 in Blackfoot 01929-01-011929 01941-01-011941 Replaced by US-93 Alternate (now US-93) and US-20 (now US-26)
SH-27 26.561 42.746 Main Street in Oakley SH-25 in Paul 01950-01-011950 current
SH-28 135.645 218.299 SH-33 near Mud Lake US-93 in Salmon 01929-01-011929 current
SH-29 SH-27 (now US-26) in Arco US-91 in Dubois 01929-01-011929 01938-01-011938 Replaced by SH-22
SH-29 US-91 in Idaho Falls Wyoming border 01938-01-011938 01952-01-011952 Former portion of SH-22; replaced by US-26
SH-29 13.614 21.910 SH-28 in Leadore Montana Secondary Highway 324 at Bannock Pass 01953-01-011953 current
SH-31 US-191 (now US 20) in Island Park Montana state line at Raynolds Pass 01929-01-011929 01934-01-011934 Later restored as SH-96, later SH-287, now later SH-87
SH-31 21.025 33.836 US-26 in Swan Valley SH-33 in Victor 01934-01-011934 current
SH-32 28.386 45.683 SH-33 near Tetonia SH-47 near Ashton 01929-01-011929 current
SH-33 155.084 249.584 US-20 / US-26 near Arco WYO 22 near Victor 01929-01-011929 current
SH-34 105.980 170.558 US-91 / SH-36 in Preston WYO 239 near Freedom 01929-01-011929 current Formerly continued south to the Utah border
SH-35 SH-40 (now US-89) in Geneva Utah state line 01929-01-011929 01939-01-011939 Replaced by US-89
SH-35 US-91 in Red Rock Junction Utah state line 01953-01-011953 01962-01-011962 Now Old Oxford Highway and Oxford Highway
SH-36 US-91 in Downey Utah state line 01929-01-011929 01938-01-011938 replaced by US-191 (now I-15)
SH-36 73.313 117.986 I-15 near Malad City US-89 in Ovid 01962-01-011962 current
SH-37 31.231 50.261 OnediaPower county line near Holbrook I-86 near American Falls 01929-01-011929 current Formerly continued to Malad City
SH-38 Power/Bannock County Line south of Pocatello SH-37 east of Holbrook 01929-01-011929 01960-01-011960 Now Arbon Valley Road, Arbon Valley Highway, and Bannock Highway; continued north to Pocatello until 1955
SH-38 23.438 37.720 North Holbrook Road near Holbrook I-15 in Malad City 01985-01-011985 current Formerly part of SH-37
SH-39 52.924 85.173 I-86 in American Falls US-26 in Blackfoot 01929-01-011929 current
SH-40 Wyoming state line SH-35 (now US-89) in Geneva 01929-01-011929 01939-01-011939 Replaced by US-89
SH-40 2.737 4.405 I-15 near Downey US-91 in Downey 01972-01-011972 current
SH-41 39.058 62.858 I-90 in Post Falls US-2 in Oldtown 01931-01-011931 current
SH-42 SH-7 in Kendrick US-12 near Spalding 01934-01-011934 01965-01-011965 Replaced by SH-3; originally continued north to Harvard
SH-43 SH-7 in Ahsahka SH-42 in Kendrick 01934-01-011934 01946-01-011946 Restored as part of rerouted SH-7 in 1953; now Old Highway 7
SH-43 US-95 Alternate near Santa Elk River 01953-01-011953 01965-01-011965 Replaced by SH-3 and SH-8
SH-43 3.868 6.225 US-26 at Beachs Corner US-20 in Ucon 01978-01-011978 current
SH-44 23.089 37.158 I-84 near Caldwell US-20 / US-26 in Garden City 01934-01-011934 current
SH-45 17.985 28.944 SH-78 at Walters Ferry I-84 Business in Nampa 01934-01-011934 current
SH-46 43.052 69.285 I-84 near Wendell US-20 near Fairfield 01935-01-011935 current
SH-47 12.420 19.988 US-20 near Warm River Wyoming state line 01935-01-011935 01957-01-011957
SH-47 12.420 19.988 US-20 in Ashton Caribou-Targhee National Forest near Warm River 01958-01-011958 current
SH-48 24.409 39.282 I-15 near Roberts US-26 Business in Ririe 01935-01-011935 current
SH-49 Washington state line US-95 near Parma 01937-01-011937 01940-01-011940 Replaced by US-20 (US-26 was added to this section of US-20 as a concurrency in 1952)
SH-49 SH-48 near Menan 97th north near Idaho Falls 01953-01-011953 01962-01-011962 Until 1957, continued south to US 20/US 191 (now Business US 20); now 5th East/3400 East, 100 North, and 3500 East
SH-50 8.092 13.023 US-30 near Kimberly SH-25 near Eden 01938-01-011938 current
SH-51 93.598 150.631 Nevada State Route 225 near Owyhee, Nevada I-84 Business in Mountain Home 01938-01-011938 current
SH-52 54.126 87.107 OR 52 in Payette SH-55 in Horseshoe Bend 01938-01-011938 current
SH-52A 54.126 87.107 Payette River SH-52 near Emmett 01953-01-011953 01973-01-011973 now Black Canyon Highway
SH-53 14.255 22.941 SR 290 near State Line US-95 near Hayden 01938-01-011938 current
SH-54 15.440 24.848 SH-41 in Spirit Lake Main Avenue in Bayview 01953-01-011953 current
SH-55 US-2 in Colburn US-10 Alternate near Kootenai 01953-01-011953 01955-01-011955 now Colburn-Culver Road
SH-55 156.047 251.133 US-95 near Marsing US-95 in New Meadows 01967-01-011967 current
SH-56 US-95 in Sagle Garfield 01953-01-011953 01955-01-011955 now Sagle Road, Glengary Road, and Garfield Cutoff Road
SH-57 37.230 59.916 US-2 in Priest River Reeder Creek Road in Nordman 01953-01-011953 current
SH-58 2.943 4.736 SR 278 near Rockford, Washington US-95 near Worley 01953-01-011953 current
SH-60 5.510 8.867 SR 274 near Tekoa, Washington US-95 near Tensed 01959-01-011959 current
SH-61 0.740 1.191 WYO 89 near Geneva US-89 in Geneva 01953-01-011953 current
SH-62 15.410 24.800 US-95 Business in Craigmont SH-64 / SH-162 in Nezperce 01953-01-011953 current
SH-64 15.409 24.798 SH-62 / SH-162 in Nezperce SH-162 in Kamiah 01962-01-011962 current Originally continued west to Craigmont
SH-66 0.992 1.596 Palouse Cove Road near Palouse, Washington US-95 near Viola 01953-01-011953 current
SH-67 8.948 14.400 Mountain Home Air Force Base SH-51 in Mountain Home 01953-01-011953 current
SH-68 US-30 in Mountain Home US-20 Temp / US-26 in Carey 01953-01-011953 01978-01-011978 Replaced by rerouted US-20
SH-69 8.012 12.894 Orchard Avenue in Kuna I-84 / US-30 / SH-55 in Meridian 01953-01-011953 current
SH-70 Eaton Road near Eaton US-95 Business in Weiser 01953-01-011953 01977-01-011977 Now County Road 70
SH-71 28.730 46.236 US-95 in Cambridge OR 86 near Brownlee Dam 01956-01-011956 current
SH-72 US-95 near Marsing US-30 near Nampa 01953-01-011953 01967-01-011967 Renumbered as part of SH-55
SH-72 1.989 3.201 US-30 near New Plymouth SH-52 at Hamilton Corner 01972-01-011972 current Former alignment of US-30
SH-73 US-30 in Buhl Castleford 01953-01-011953 01953-01-011953 Now 1400 East, 3700 North, 1200 East, and 3600 North
SH-73 US-30 in New Plymouth I-84 01965-01-011965 01972-01-011972 Replaced by rerouted US-30
SH-74 7.835 12.609 US-93 near Knull US-30 in Twin Falls 01953-01-011953 current
SH-75 US-93 in Ketchum Sun Valley 01953-01-011953 01977-01-011977 For a time continued northeast to Chilly; redesignated as a spur of the current route
SH-75 170.666 274.660 US-26 / US-93 in Shoshone US-93 near Challis 01977-01-011977 current Former alignment of US-93
SH-76 1420 North north of Richfield US-26 in Richfield 01953-01-011953 01954-01-011954 Now 3rd Street and Center Road
SH-77 30.676 49.368 SH-81 in Malta I-84 / SH-25 near Declo 01953-01-011953 current
SH-78 99.720 160.484 SH-55 in Marsing I-84 Business in Hammett 01972-01-011972 current
SH-79 2.564 4.126 I-84 in Jerome SH-25 in Jerome 01953-01-011953 current
SH-80 SH-48 in Menan US-20 in Lorenzo 01953-01-011953 01962-01-011962 Now Menan-Lorenzo Highway
SH-81 33.978 54.682 SH-77 in Malta US-30 in Burley 01970-01-011970 current
SH-84 US-20 in Macks Inn Big Springs 01953-01-011953 01977-01-011977 Now Big Springs Loop Road
SH-86 West Side Highway (formerly SH-35) in Dayton US-91 in Preston 01953-01-011953 01964-01-011964 Removed from the state highway system; restored in 1985 as part of SH-36
SH-87 9.133 14.698 US-20 in Island Park MT 87 at Raynolds Pass 01967-01-011967 current
SH-88 US-20 / US-26 near Arco US-20 in Rexburg 01953-01-011953 01977-01-011977 Replaced by SH-33
SH-96 9.133 14.698 US-20 in Island Park MT 287 at Raynolds Pass 01959-01-011959 01960-01-011960 renumbered SH-287 to match Montana; later renumbered SH-87 on both sides of the border
SH-97 35.745 57.526 SH-3 near Harrison I-90 near Coeur d'Alene 01977-01-011977 current
SH-99 11.686 18.807 SH-3 in Kendrick SH-8 in Troy 01961-01-011961 current
SH-128 2.198 3.537 SR 128 near Lewiston US-12 in Lewiston 01989-01-011989 current
SH-162 31.077 50.014 SH-62 / SH-64 in Nezperce US-12 in Kamiah 01993-01-011993 current Former portion of SH-62
SH-167 16.319 26.263 SH-78 in Grand View SH-67 near Mountain Home Air Force Base 02010-01-012010 current Former portion of SH-67
SH-200 33.169 53.380 US-2 / US-95 in Ponderay MT 200 near Clark Fork 01967-01-011967 current Formerly U.S. Route 10 Alternate
SH-287 9.133 14.698 US-20 in Island Park MT 287 at Raynolds Pass 01960-01-011960 01967-01-011967 renumbered SH-87 when Montana renumbered Highway 287 to Highway 87

See also


  1. ^ "Frequently Asked Questions". Idaho Transportation Department. Retrieved February 15, 2017.
  2. ^ a b Rand McNally Auto Road Atlas, 1926, accessed via the Broer Map Library
  3. ^ Senate Concurrent Resolution No. 8, "a concurrent permit Charles B. Sampson to extend the marking system of the Sampson Trail..." passed February 16, 1933
  4. ^ Lawson, H. A. (March 25, 1929). "Blazing Western Trails is Unique Hobby of Idahoan". Daily Herald. p. 3. Retrieved April 21, 2019 – via
  5. ^ H.M. Gousha Company, Western States road map, published by Standard Oil Company of California, 1935
  6. ^ Rand McNally and Company, Road map: Idaho, Mont., Wyo., published by Texaco, 1937
  7. ^ "Colored US highway shields". US ends .com. April 5, 2020. Retrieved April 26, 2020.
  8. ^ "Traffic Manual: Idaho Supplementary Guidance to the MUTCD" (PDF). Idaho Transportation Department. April 2020. pp. 37–38, 60. Retrieved April 26, 2020.
  9. ^ "Milepoint Logs". Idaho Transportation Department. Archived from the original on February 16, 2017. Retrieved February 15, 2017.
  10. ^ Downing, T.A. (April 15, 1937). "Designated Federal and State Highways Minute Book 09". Idaho Bureau of Highways. Retrieved October 3, 2018 – via Idaho State Archives.

External links