County profile · official public datasets

Lyman County, SD

114 public highway bridges tracked in the FHWA National Bridge Inventory: 40.4% rated Good, 50% Fair, 9.6% Poor.

114
Public bridges: 40.4%
Good condition: 9.6%
Poor condition

The verdict

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

Lyman County posts a better-than-median Poor-condition share among rated counties in the state across mid-size county bridge inventory.

Top 29%
lowest Poor share in state: 9.6%
Poor-condition share: 114
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.

Lyman County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Lyman County ranks #19 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 9.6%). Lyman County, South Dakota contains 114 public highway bridges. Roughly 40.4% are rated “Good,” 50% “Fair,” and 9.6% “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

114

Public highway bridges in Lyman County

Good condition

40.4%

46 of 114 rated 7-9

Fair condition

50%

57 of 114 rated 5-6

Poor condition

9.6%

11 of 114 rated 4 or below

In-state Poor-share rank

#19 of 66

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

Condition distribution

Share of 114 NBI-tracked bridges by lowest applicable component rating.

Good

40.4% (46)

Fair

50% (57)

Poor

9.6% (11)

Lyman County's Poor-condition bridges carry 3,480 vehicle crossings a day

That is 1.9% of the county's reported daily bridge traffic on 9.6% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 316 crossings a day against 1,577 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 114 of 114 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

66.7% of Lyman County's bridges have passed the 50-year mark

76 of the 114 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 40.4% 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 75.3% of the county's Poor-condition bridge traffic

I090 WF over R&W RR, built 1953, carries 2,622 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 11-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 3,480 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

1
1930s

7
1940s

5
1950s

9
1960s

12
1970s

44
1980s

4
1990s

4
2000s

19
2010s

9

What this shows Construction peaked in the 1970s, when 44 of the county's bridges still in the inventory were built, which is 38.6% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1975) matches the South Dakota average (1975).

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

The 5 South Dakota counties nearest Lyman County in number of bridges, with their condition splits. Its 9.6% Poor share is the 1st-lowest of these 6. Its average build year of 1975 against a peer-group mean of 1970 is 5 years newer.

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

Bridge inventory size and condition shares for Lyman County and the 5 South Dakota counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Bon Homme County	126	21.4%	50.8%	27.8%	1961
Hand County	126	24.6%	46%	29.4%	1961
Davison County	123	34.1%	48.8%	17.1%	1973
Lyman County (this page)	114	40.4%	50%	9.6%	1975
Charles Mix County	103	38.8%	37.9%	23.3%	1971
Yankton County	99	41.4%	43.4%	15.2%	1983

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

Similar inventory size

Nearest county inventories outside SD (114 bridges here).

Calhoun County, AR · 114 bridges
Schuyler County, IL · 114 bridges
Brown County, IN · 114 bridges
Morgan County, KY · 114 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 114 Good 46 Fair 57 Poor 11

Fair-condition bridges (57)

Sort:

Lyman County Bridge Snapshot

Condition distribution

Lyman County's Poor-condition bridges carry 3,480 vehicle crossings a day

66.7% of Lyman County's bridges have passed the 50-year mark

One structure carries 75.3% of the county's Poor-condition bridge traffic

How Lyman 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

Fair-condition bridges (57)

338th Avenue

N. Main Streek

291st Avenue

SD 248 EF

313th Avenue

I090 WF

SD248

I090 W

I090 E

241st Street

240th Street

303rd Avenue

312th Avenue

241st Street

338th Avenue

241st Street

2nd St. in Presho

STATE HWY 47

SD248

299th Street

SD047

I090 W

268th Street

I090 W

I090 E

SD047

I090 W

I090 E

Deer Valley Road

US083

I090 W

I090 E

I090 W

I090 E

I090 W

I090 E

US183

I090 W

I090 E

I090 W

I090 W

I090 E

I090 W

I090 W

I090 E

I090 E

IRR AR SD273

IRR AR SD273

IRR SD1806

IRR SD1806

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