South Dakota/Highway Classification

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With the permission of user elijahmathews, I (SD Mapman) have heavily based this page off of the ND highway classification page.

General Guidelines

These are based off of what the current state of classification is in South Dakota plus the new trunk road guidance.

  • highway=motorway - This should only apply to I-90, I-29, I-229, and I-190. South Dakota has no non-interstate freeways, with only 6 "motorway islands" throughout the state (US 16/16A, Cambell St/Elk Vale Rd (Rapid City), Elk Vale Rd/SD 44, SD 50 Vermillion West, SD 50 Vermillion East, and US 14 Brookings West).
  • highway=trunk - This should apply to high-speed divided highways in addition to a set of long-haul two-lane highways connecting major cities (list and discussion below).
    • expressway=yes - Rurally, this should apply to the Heartland Expressway (SD 79 from Nebraska to Rapid City), the Eastern Dakota & Pierre expressway system (US 83 from I-90 to Pierre, SD 37 from I-90 Exit 330 to Huron, US 12 from Aberdeen to I-29, US 281 from SD 20 to Aberdeen, and SD 50 from Yankton to I-29), US 85 between Spearfish and Belle Fourche, and US 16 between Keystone and Rapid City. In Sioux Falls, this should apply to Russell St between I-29 and Minnesota Ave and the future SD 100/Veterans Parkway. In Rapid City, this should apply to the Catron Blvd/Elk Vale Rd beltway along the east side of town.
  • highway=primary - This should be used for any remaining US highways and signed Interstate Business routes along with the most important state highways.
  • highway=secondary - This should be used for the remaining state highways along with unusually important county roads.
    • If a county road and state highway are marked as secondary in the same geographic area, check to see if they are in fact of similar classification level and if not, mark the state highway as higher than the county road.
  • highway=tertiary - This should be used for most county roads.
  • highway=unclassified - This should be used for the remaining unpaved gravel roads.

Population Centers

The following is a list of the twenty largest cities in South Dakota, along with their populations as of the 2020 United States census and the major highways that serve them.

City Population Highways
Sioux Falls 192,517
Rapid City 74,703
Aberdeen 28,495
Brookings 23,377
Watertown 22,655
Mitchell 15,660
Yankton 15,411
Huron 14,263
Pierre 14,091
Spearfish 12,193
Box Elder 11,746
Vermillion 11,695
Brandon 11,048
Sturgis 7,020
Harrisburg 6,732
Madison 6,191
Belle Fourche 5,617
Tea 5,598
Dell Rapids 3,996
Milbank 3,554

Note: Dell Rapids and Milbank can probably be removed from consideration, but I included them to fill out an even table.

Additionally, since the population of South Dakota is heavily weighted toward East River, the 10 largest cities in West River are presented below.

City Population Highways
Rapid City 74,703
Spearfish 12,193
Box Elder 11,746
Sturgis 7,020
Belle Fourche 5,617
Hot Springs 3,395
Lead 2,982
Summerset 2,972
Fort Pierre 2,115
Custer 1,919

Inventory and proposals

In all tables below, a city name in bold as a terminus denotes that the highway classification reaches its terminus at the state border.

Motorways

Proposal

South Dakota's motorways are primarily limited to I-29 and I-90, which are limited-access freeways for their entire lengths across the state.

Mainline motorway system
Highway S/W Terminus N/E Terminus Length (mi)
Dakota Dunes Rosholt 253
Spearfish Valley Springs 413

There are additional limited-access freeways in Rapid City and Sioux Falls, I-190 and I-229. There are no non-Interstate full freeways in SD, with non-interstate grade separation limited to isolated interchanges.

Additional motorway system
Highway S/W Terminus N/E Terminus Length (mi)
Rapid City Rapid City 1
Tea Sioux Falls 10

Trunk highways

Proposal

The previous interpretation of "trunk highway" in South Dakota was effectively high-speed divided/four-lane highway. The proposed trunk highway network below is largely an expansion of the previous network of trunk highways. Any necessary cross-state collaboration will be discussed when the issue arises.

Note: SD mileposts are based off the WY/MT border (for E-W routes) and the NE border (for N-S routes). This can lead to routes having a "zero" milepost of 354 (e.g.) depending on where they start. Terminus in this case refers to the terminus of the trunk segment of the route, not necessarily the route itself. CURRENTLY WORKING ON TABLE 4/21/23

Proposed rural trunk highway network
Highway S/W Terminus City N/E Terminus City S/W Terminus Milepost N/E Terminus Milepost Length (mi) Justification/Comments
US 12 Lemmon Big Stone City 80.50 399.74 319.24 US 12 is the major E-W collector route for Northern SD, linking Lemmon, Mobridge, and Aberdeen with the Bakken to the west and the Twin Cities to the east.
SD 34 Sturgis Hayes 33.89 170.45 136.56 SD 34 in combination with US 14 East River is the major E-W collector route for Central SD, linking Sturgis, Pierre, Huron, and Brookings. This route continues into MN towards Mankato.
US 14 Hayes Brookings 190.03 418.40 228.37 US 14 in combination with SD 34 West River is the major E-W collector route for Central SD, linking Sturgis, Pierre, Huron, and Brookings. This route continues into MN towards Mankato.
US 14 Bypass Brookings Brookings 418.11 423.24 5.13 Bypass for through traffic around Brookings.
US 14 Brookings Elkton 423.19 439.75 16.56 US 14 in combination with SD 34 West River is the major E-W collector route for Central SD, linking Sturgis, Pierre, Huron, and Brookings. This route continues into MN towards Mankato.
SD 50 Yankton Burbank 383.83 417.02 33.19 SD 50 between Yankton and I-29 forms part of the Eastern Dakota Expressway system, linking one of the larger cities in the state and one of the state universities with I-29.
US 18 Edgemont Hot Springs 0.00 62.27 62.27 US 18 serves as the link from Wyoming and Colorado to the Heartland Expressway. This is the most convenient route for travelers from Rapid City and points east to reach Cheyenne, Casper, and Denver. Partially concurrent with US 385 and SD 79. Due to South Dakota's milepost priority system, this also includes the Heartland Expressway system from Hot Springs to Oelrichs.
US 385 Oelrichs Oelrichs 0.00 13.08 13.08 This is part of the Heartland Expressway, which was intended to be a four-lane divided highway linking Denver and Rapid City.
SD 79 Hot Springs Rapid City 27.00 74.54 47.54 This is part of the Heartland Expressway, which was intended to be a four-lane divided highway linking Denver and Rapid City.
US 16 Truck Rapid City Rapid City 64.19 73.11 8.92 Bypass for through traffic around Rapid City. Contains part of the Heartland Expressway.
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