County profile · official public datasets

Hillsborough County, NH

385 public highway bridges tracked in the FHWA National Bridge Inventory: 51.4% rated Good, 39.7% Fair, 8.8% Poor.

385
Public bridges: 51.4%
Good condition: 8.8%
Poor condition

The verdict

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

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

9th
of 10 on Poor share: 8.8%
Poor-condition share: 385
public highway bridges: 1972
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.

Hillsborough County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Hillsborough County ranks #9 of 10 New Hampshire counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 8.8%). Hillsborough County, New Hampshire contains 385 public highway bridges. Roughly 51.4% are rated “Good,” 39.7% “Fair,” and 8.8% “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

385

Public highway bridges in Hillsborough County

Good condition

51.4%

198 of 385 rated 7-9

Fair condition

39.7%

153 of 385 rated 5-6

Poor condition

8.8%

34 of 385 rated 4 or below

In-state Poor-share rank

#9 of 10

Among New Hampshire counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 385 NBI-tracked bridges by lowest applicable component rating.

Good

51.4% (198)

Fair

39.7% (153)

Poor

8.8% (34)

Hillsborough County's Poor-condition bridges carry 262,941 vehicle crossings a day

That is 5.9% of the county's reported daily bridge traffic on 8.8% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 7,734 crossings a day against 12,328 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 385 of 385 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

50.9% of Hillsborough County's bridges have passed the 50-year mark

196 of the 385 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 51.4% 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 17.1% of the county's Poor-condition bridge traffic

I-293 FEE TPK over STARK WAY, built 1956, carries 45,069 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 34-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 262,941 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

pre-1900

3
1900s

10
1910s

6
1920s

18
1930s

37
1940s

18
1950s

42
1960s

41
1970s

39
1980s

22
1990s

48
2000s

47
2010s

46
2020s

8

What this shows Construction peaked in the 1990s, when 48 of the county's bridges still in the inventory were built, which is 12.5% of those with a recorded year. That cohort is now 25 to 34 years old in the 2024 inventory. Its average build year (1972) matches the New Hampshire average (1968).

How Hillsborough County compares with New Hampshire's closest counties by inventory size

The 5 New Hampshire counties nearest Hillsborough County in number of bridges, with their condition splits. Its 8.8% Poor share is the 5th-lowest of these 6. Its average build year of 1972 against a peer-group mean of 1967 is 5 years newer.

Showing the 5 closest of 9 New Hampshire counties eligible for comparison.

Bridge inventory size and condition shares for Hillsborough County and the 5 New Hampshire counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Grafton County	544	47.8%	44.1%	8.1%	1966
Hillsborough County (this page)	385	51.4%	39.7%	8.8%	1972
Merrimack County	326	45.1%	46.9%	8%	1966
Rockingham County	308	66.6%	26.9%	6.5%	1977
Carroll County	193	54.9%	40.9%	4.1%	1966
Cheshire County	192	41.7%	46.9%	11.5%	1960

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 Hillsborough 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 Hillsborough County, both outside New Hampshire so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside NH (385 bridges here).

Lee County, MS · 385 bridges
Calhoun County, AL · 386 bridges
Stanislaus County, CA · 386 bridges
Gibson County, TN · 386 bridges

Similar average build year

Nearest mean year-built outside NH (1972 here).

Santa Clara County, CA · avg 1972 · 964 bridges
Madison County, AL · avg 1972 · 710 bridges
Kern County, CA · avg 1972 · 668 bridges
York County, PA · avg 1972 · 569 bridges

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

All 385 Good 198 Fair 153 Poor 34

All bridges (385)

Sort:

Hillsborough County Bridge Snapshot

Condition distribution

Hillsborough County's Poor-condition bridges carry 262,941 vehicle crossings a day

50.9% of Hillsborough County's bridges have passed the 50-year mark

One structure carries 17.1% of the county's Poor-condition bridge traffic

How Hillsborough County compares with New Hampshire'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 (385)

CLARKVILLE ROAD

BEARD ROAD

OLD BRIDGE STREET

FOREST ROAD

NH101

ANTRIM ROAD

SHEDD ROAD

DANFORTH CORNERS

NORTH ROAD

GROVE STREET

COOLEDGE ROAD

E WASHINGTON ROAD

WHITTEN ROAD

PURGATORY ROAD

LUND ROAD

POOR FARM ROAD

DANIEL WEBSTER HWY

MASON ROAD

NH149

NH 77 TRUCK ROUTE

NH 31

CROSS ROAD

LINK ROAD

US 3 ELM ST

MILL ROAD

NH 77

NH130

WILTON ROAD

NH 9 NH 31

FEE TPK NB

CANAL STREET

NH101

NH 13

SHARON ROAD

NH 31

BOND STREET

NH 13

MORRISON ROAD

ACCESS ROAD

NH101

NH 31

OLD COUNTY RD S

NH 28A MAMMOTH RD

ALLDS STREET

SAW MILL ROAD

OLD NH 9

NH111

NH 31

GREGG MILL ROAD

BURTON HIGHWAY

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