County profile · official public datasets

Tripp County, SD

90 public highway bridges tracked in the FHWA National Bridge Inventory: 27.8% rated Good, 44.4% Fair, 27.8% Poor.

90
Public bridges: 27.8%
Good condition: 27.8%
Poor condition

The verdict

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

Tripp County posts a higher-than-median Poor-condition share among rated counties in the state across rated county bridge inventory.

59th
of 66 on Poor share: 27.8%
Poor-condition share: 90
public highway bridges: 1975
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.

Tripp County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Tripp County ranks #59 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 27.8%). Tripp County, South Dakota contains 90 public highway bridges. Roughly 27.8% are rated “Good,” 44.4% “Fair,” and 27.8% “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

Public highway bridges in Tripp County

Good condition

27.8%

25 of 90 rated 7-9

Fair condition

44.4%

40 of 90 rated 5-6

Poor condition

27.8%

25 of 90 rated 4 or below

In-state Poor-share rank

#59 of 66

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

Condition distribution

Share of 90 NBI-tracked bridges by lowest applicable component rating.

Good

27.8% (25)

Fair

44.4% (40)

Poor

27.8% (25)

Tripp County's Poor-condition bridges carry 1,671 vehicle crossings a day

That is 5.4% of the county's reported daily bridge traffic on 27.8% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 67 crossings a day against 119 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 90 of 90 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

61.1% of Tripp County's bridges have passed the 50-year mark

55 of the 90 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 27.8% 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 30.5% of the county's Poor-condition bridge traffic

SD049 over CK, built 1972, carries 509 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 25-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 1,671 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

1
1930s

3
1940s

6
1950s

20
1960s

18
1970s

7
1980s

11
1990s

1
2000s

10
2010s

9
2020s

4

What this shows Construction peaked in the 1950s, when 20 of the county's bridges still in the inventory were built, which is 22.2% of those with a recorded year. That cohort is now 65 to 74 years old in the 2024 inventory. Its average build year (1975) matches the South Dakota average (1975).

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

The 5 South Dakota counties nearest Tripp County in number of bridges, with their condition splits. Its 27.8% Poor share is the 6th-lowest of these 6. Its average build year of 1975 against a peer-group mean of 1976 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 Tripp County and the 5 South Dakota counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
McCook County	98	44.9%	44.9%	10.2%	1977
Custer County	95	46.3%	48.4%	5.3%	1977
Clay County	94	58.5%	25.5%	16%	1985
Tripp County (this page)	90	27.8%	44.4%	27.8%	1975
Jackson County	89	29.2%	55.1%	15.7%	1969
Moody County	87	29.9%	46%	24.1%	1973

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 Tripp 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 Tripp County, both outside South Dakota so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside SD (90 bridges here).

Greenlee County, AZ · 90 bridges
Clay County, FL · 90 bridges
Taylor County, FL · 90 bridges
Monroe County, GA · 90 bridges

Similar average build year

Nearest mean year-built outside SD (1975 here).

San Bernardino County, CA · avg 1975 · 1,422 bridges
Lane County, OR · avg 1975 · 1,010 bridges
Fulton County, GA · avg 1975 · 775 bridges
Westmoreland County, PA · avg 1975 · 620 bridges

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

All 90 Good 25 Fair 40 Poor 25

All bridges (90)

Sort:

Tripp County Bridge Snapshot

Condition distribution

Tripp County's Poor-condition bridges carry 1,671 vehicle crossings a day

61.1% of Tripp County's bridges have passed the 50-year mark

One structure carries 30.5% of the county's Poor-condition bridge traffic

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

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

All bridges (90)

270 STREET

285 STREET

327 AVENUE

272 STREET

272 STREET

289 STREET

303 AVENUE

315 AVENUE

303 AVENUE

272 STREET

296 STREET

300 AVENUE

US183

US183

266 STREET

SD053

282 STREET

331 AVENUE

257 ST

US018

SD044

SD049

318 AVENUE

US018

US183

US018

SD044

SD044

US018

US018

SD049

US018

SD049

US018 SER RD

US018

280 STREET

SD044

US183

US018

US018

300 STREET

316 AVENUE

275 STREET

288 STREET

273 STREET

296 STREET

304 AVENUE

314 AVENUE

331 AVENUE

SD044

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