South Dakota/Highway Classification
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.
| 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.
| Highway | S/W Terminus | N/E Terminus | Length (mi) |
|---|---|---|---|
| Rapid City | Rapid City | 1 | |
| Sioux Falls | Tea | 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
| 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. |