County profile · official public datasets

Mellette County, SD

28 public highway bridges tracked in the FHWA National Bridge Inventory: 32.1% rated Good, 60.7% Fair, 7.1% Poor.

28
Public bridges
32.1%
Good condition
7.1%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Mellette County pairs a top-quartile lowest Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 23%
lowest Poor share in state
7.1%
Poor-condition share
28
public highway bridges
1980
avg year built

Poor is an FHWA condition category from the lowest applicable component rating (4 or below), not a live crossing-safety or closure decision. Rankings cover counties with at least five public highway bridges.

Mellette County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Mellette County ranks #15 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 7.1%). Mellette County, South Dakota contains 28 public highway bridges. Roughly 32.1% are rated “Good,” 60.7% “Fair,” and 7.1% “Poor.” Poor means the lowest applicable deck, superstructure, substructure, or culvert rating is 4 or below on the 0–9 NBI scale. It is a condition category, not a live safety or closure decision.

Responsible agencies inspect covered bridges on risk-based intervals under current NBIS rules and submit inventory data to FHWA annually. The list below shows every NBI-tracked bridge in the county. Use the “Sort by” controls to change the ordering, and click any row for its reported inspection date, traffic count, and condition fields.

Source: FHWA National Bridge Inventory. See methodology for full definitions.

Total bridges

28

Public highway bridges in Mellette County

Good condition

32.1%

9 of 28 rated 7-9

Fair condition

60.7%

17 of 28 rated 5-6

Poor condition

7.1%

2 of 28 rated 4 or below

In-state Poor-share rank

#15 of 66

Among South Dakota counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 28 NBI-tracked bridges by lowest applicable component rating.

Good
32.1% (9)
Fair
60.7% (17)
Poor
7.1% (2)

Mellette County's Poor-condition bridges carry 19 vehicle crossings a day

That is 0.2% of the county's reported daily bridge traffic on 7.4% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 10 crossings a day against 652 for a Good-condition one. A Poor rating is a condition category, not a closure or a live safety judgement; it means the lowest applicable component rating is 4 or below.

Computed over the 27 of 28 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

50% of Mellette County's bridges have passed the 50-year mark

14 of the 28 bridges with a recorded construction year were built in 1974 or earlier. Age alone is not a defect: a well-maintained older bridge can rate Good, and 32.1% of this county's inventory does. Even so, this older cohort is the population from which future Poor ratings are drawn, which is why the age profile below matters alongside the condition split above.

Cutoff derives from the 2024 release year minus a 50-year design life. Source: FHWA National Bridge Inventory, 2024 release.

One structure carries 52.6% of the county's Poor-condition bridge traffic

PINE CREEK (UNORG) over PINE CK, built 1992, carries 10 vehicles a day, the most of any Poor-rated structure here. The county's Poor-condition exposure is concentrated rather than evenly spread, so the 2-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 19 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

When Mellette County's bridges were built

28 bridges with a recorded construction year, grouped by decade

bridges

What this shows Construction peaked in the 1980s, when 7 of the county's bridges still in the inventory were built, which is 25% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year is 1980, 5 years newer than the South Dakota average of 1975.

Source FHWA National Bridge Inventory (year built) As of 2024 NBI release

How Mellette County compares with South Dakota's closest counties by inventory size

The 5 South Dakota counties nearest Mellette County in number of bridges, with their condition splits. Its 7.1% Poor share is the 3rd-lowest of these 6. Its average build year of 1980 against a peer-group mean of 1978 is in line with the group.

Showing the 5 closest of 65 South Dakota counties eligible for comparison.

Bridge inventory size and condition shares for Mellette County and the 5 South Dakota counties closest to it in inventory size
County Bridges Poor
Sully County 31 19.4%
Ziebach County 30 10%
Dewey County 28 14.3%
Mellette County (this page) 28 7.1%
Buffalo County 25 4%
Potter County 24 0%

Each share is of that county's own total tracked bridges; peers are the counties with 5 or more bridges whose inventory size is closest to Mellette County's. Source: FHWA National Bridge Inventory, 2024 release.

Nationwide counties with similar inventory size or average build year

Two NBI-derived peer sets for Mellette County, both outside South Dakota so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside SD (28 bridges here).

Similar average build year

Nearest mean year-built outside SD (1980 here).

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 28 Good 9 Fair 17 Poor 2

All bridges (28)

SD044

Fair

Over: LITTLE WHITE RV

0.7 W JCT US 83, Mellette, SD

Built 1973 Load: 21.0 t ADT: 802

COUNTY HIGHWAY #9

Fair

Over: GRAY EAGLETAIL CK

11E & 4.5S NORRIS, Mellette, SD

Built 1960 Load: 21.2 t ADT: 53

COUNTY HIGHWAY #23

Fair

Over: WHITE HORSE CK

4S MOSHER, Mellette, SD

Built 1957 Load: 21.2 t ADT: 55

COUNTY HIGHWAY #9

Fair

Over: LITTLE WHITE RV

11.6S & 4.3W WHITE RIVER, Mellette, SD

Built 1970 Load: 22.3 t ADT: 18

COUNTY HIGHWAY #11

Fair

Over: LITTLE WHITE RV

10.7N & 4.8E WHITE RIVER, Mellette, SD

Built 1962 Load: 22.4 t ADT: 35

COUNTY HIGHWAY #23

Fair

Over: OAK CK

3S MOSHER, Mellette, SD

Built 1957 Load: 23.3 t ADT: 63

SD063

Fair

Over: BLACK PIPE CK

1.8 E OF NORRIS, Mellette, SD

Built 1954 Load: 29.8 t ADT: 289

IRR AR SD063

Fair

Over: SIMMS CK

10 N JCT SD 44, Mellette, SD

Built 1959 Load: 32.2 t ADT: 159

IRR AR SD063

Fair

Over: BLACK PIPE CK

2.3 N JCT SD 44 E, Mellette, SD

Built 1959 Load: 32.4 t ADT: 159

SD044

Fair

Over: WHITE THUNDER CK

2 W OF WOOD, Mellette, SD

Built 1981 Load: 36.3 t ADT: 271

IRR AR US083

Fair

Over: HORSE HEAD CK

3.1 S JCT SD 44 E, Mellette, SD

Built 1966 Load: 39.2 t ADT: 1,558

IRR AR SD063

Fair

Over: BLACK PIPE CK

0.1 SE JACKSON CO LINE, Mellette, SD

Built 1970 Load: 41.6 t ADT: 159

SD044

Fair

Over: BLACK PIPE CK

0.3 E JCT SD 63, Mellette, SD

Built 1987 Load: 41.6 t ADT: 328

SD044

Fair

Over: PINE CK

2.3 W JCT US 83, Mellette, SD

Built 1973 Load: 41.7 t ADT: 328

SD044

Fair

Over: OAK CK

2.7 W TRIPP CO LINE, Mellette, SD

Built 1989 Load: 44.0 t ADT: 318

COUNTY HIGHWAY #11

Fair

Over: CK

9.9N & 3.2E WHITE RV, Mellette, SD

Built 1962 Load: 66.5 t ADT: 40

IRR AR SD063

Fair

Over: CORN CK

0.7 N JCT SD 44 E, Mellette, SD

Built 1991 Load: 79.1 t ADT: 159

IRR AR SD063

Good

Over: CHURCH CK

4.8 N JCT 44 E, Mellette, SD

Built 2003 Load: 25.1 t ADT: 159

US083

Good

Over: LITTLE WHITE RV

2 N OF WHITE RIVER, Mellette, SD

Built 2022 Load: 32.9 t ADT: 1,375

IRR AR SD044

Good

Over: CORN CK

0.6 W JCT SD 63, Mellette, SD

Built 1980 Load: 36.8 t ADT: 455

C HY 6/STAMFORD RD

Good

Over: WHITE RV

18.9N & 0.8W CEDAR BUTTE, Mellette, SD

Built 2017 Load: 42.3 t ADT: 85

US083

Good

Over: WHITE RV

JONES-MELLETTE CO LINE, Mellette, SD

Built 2021 Load: 45.3 t ADT: 1,375

SD053

Good

Over: BUTTE CK

1.8 N JCT SD 44, Mellette, SD

Built 2004 Load: 45.3 t ADT: 106

SD053

Good

Over: BUTTE CK

0.6 N JCT SD 44, Mellette, SD

Built 1989 Load: 47.2 t ADT: 106

IRR AR US083

Good

Over: CK

2.3 S JCT SD 44 E, Mellette, SD

Built 1965 Load: 53.5 t ADT: 1,558

SD063

Good

Over: DRY CK

0.1 N OF NORRIS, Mellette, SD

Built 1984 Load: 64.2 t

PINE CREEK (UNORG)

Poor

Over: PINE CK

5W & 0.8S WHITE RIVER, Mellette, SD

Built 1992 Load: 2.7 t ADT: 10

COUNTY HIGHWAY #7

Poor

Over: COTTONWOOD CK

5W & 4.2N WHITE RV, Mellette, SD

Built 1982 Load: 19.1 t ADT: 9

Read our methodology - how this data is sourced, computed, and verified.

Related

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Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges

Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.