Total bridges
34
Public highway bridges in Day County
County profile · official public datasets
Day County, SD
34 public highway bridges tracked in the FHWA National Bridge Inventory: 35.3% rated Good, 29.4% Fair, 35.3% Poor.
- 34
- Public bridges
- 35.3%
- Good condition
- 35.3%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Day County pairs a higher-than-median Poor-condition share among rated counties in the state with an older average build year than the state inventory.
- 66th
- of 66 on Poor share
- 35.3%
- Poor-condition share
- 34
- public highway bridges
- 1963
- 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.
Day County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Day County ranks #66 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 35.3%). Day County, South Dakota contains 34 public highway bridges. Roughly 35.3% are rated “Good,” 29.4% “Fair,” and 35.3% “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.
Good condition
35.3%
12 of 34 rated 7-9
Fair condition
29.4%
10 of 34 rated 5-6
Poor condition
35.3%
12 of 34 rated 4 or below
In-state Poor-share rank
#66 of 66
Among South Dakota counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 34 NBI-tracked bridges by lowest applicable component rating.
Good 35.3% (12)
Fair 29.4% (10)
Poor 35.3% (12)
Day County's Poor-condition bridges carry 855 vehicle crossings a day
That is 17.3% of the county's reported daily bridge traffic on 35.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 71 crossings a day against 154 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 34 of 34 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
61.8% of Day County's bridges have passed the 50-year mark
21 of the 34 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 35.3% 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 32% of the county's Poor-condition bridge traffic
425th Avenue over BURLINGTON NORTHERN RR, built 1960, carries 274 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 12-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 855 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Day County's bridges were built
34 bridges with a recorded construction year, grouped by decade
- 1920s 3
1920–1929
3 bridges
- 1930s
1930–1939
14 bridges
- 1960s 1
1960–1969
1 bridges
- 1970s 3
1970–1979
3 bridges
- 1980s 1
1980–1989
1 bridges
- 1990s 3
1990–1999
3 bridges
- 2000s
2000–2009
6 bridges
- 2010s 1
2010–2019
1 bridges
- 2020s 2
2020–2029
2 bridges
What this shows Construction peaked in the 1930s, when 14 of the county's bridges still in the inventory were built, which is 41.2% of those with a recorded year. That cohort is now 85 to 94 years old in the 2024 inventory. Its average build year is 1963, 12 years older than the South Dakota average of 1975.
How Day County compares with South Dakota's closest counties by inventory size
The 5 South Dakota counties nearest Day County in number of bridges, with their condition splits. Its 35.3% Poor share is the 6th-lowest of these 6. Its average build year of 1963 against a peer-group mean of 1972 is 9 years older.
Showing the 5 closest of 65 South Dakota counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Jones County | 37 | 13.5% | 81.1% | 5.4% | 1965 |
| Jerauld County | 35 | 20% | 54.3% | 25.7% | 1967 |
| Kingsbury County | 35 | 17.1% | 54.3% | 28.6% | 1964 |
| Oglala Lakota County | 34 | 55.9% | 38.2% | 5.9% | 1992 |
| Day County (this page) | 34 | 35.3% | 29.4% | 35.3% | 1963 |
| Walworth County | 33 | 36.4% | 60.6% | 3% | 1972 |
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 Day 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 Day County, both outside South Dakota so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside SD (34 bridges here).
- Bear Lake County, ID · 34 bridges
- Plaquemines County, LA · 34 bridges
- Golden Valley County, ND · 34 bridges
- Guayanilla County, PR · 34 bridges
Similar average build year
Nearest mean year-built outside SD (1963 here).
- Worcester County, MA · avg 1963 · 1,014 bridges
- Honolulu County, HI · avg 1963 · 682 bridges
- Chester County, PA · avg 1963 · 680 bridges
- Essex County, NJ · avg 1963 · 505 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
Fair-condition bridges (10)
414th Avenue
FairOver: Creek
5W & 2.9N Pierpont, Day, SD
Built 1930 Load: 15.1 t ADT: 15
412TH Avenue
FairOver: Creek
4 W & 3.7 N of Andover, Day, SD
Built 1985 Load: 24.5 t ADT: 69
412TH Avenue
FairOver: Creek
4 W & 1.2 N of Andover, Day, SD
Built 1934 Load: 24.5 t ADT: 69
412TH Avenue
FairOver: Mud Creek
4 W & 4.7 S of Andover, Day, SD
Built 1930 Load: 24.5 t ADT: 69
130th Street
FairOver: Creek
.5N & 3.9W of Pierpont, Day, SD
Built 1930 Load: 24.5 t ADT: 27
130th Street
FairOver: Creek
0.5N & 2.9E of Pierpont, Day, SD
Built 1935 Load: 24.5 t ADT: 385
128th Street
FairOver: Creek
2 N & 11.5 E of Roslyn, Day, SD
Built 1993 Load: 24.5 t ADT: 307
SD027
FairOver: MUD CK
8.9 S MARSHALL CO LINE, Day, SD
Built 1970 Load: 58.9 t ADT: 253
SD027
FairOver: CK
4.7 S MARSHALL CO LINE, Day, SD
Built 1970 Load: 59.4 t ADT: 518
SD027
FairOver: ANTELOPE CK
1.2 S MARSHALL CO LINE, Day, SD
Built 1970 Load: 65.8 t ADT: 518
Read our methodology - how this data is sourced, computed, and verified.
Related
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.