County profile · official public datasets

Mercer County, NJ

414 public highway bridges tracked in the FHWA National Bridge Inventory: 40.3% rated Good, 50.5% Fair, 9.2% Poor.

414
Public bridges: 40.3%
Good condition: 9.2%
Poor condition

The verdict

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

Mercer County pairs a higher-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

17th
of 21 on Poor share: 9.2%
Poor-condition share: 414
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.

Mercer County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Mercer County ranks #17 of 21 New Jersey counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 9.2%). Mercer County, New Jersey contains 414 public highway bridges. Roughly 40.3% are rated “Good,” 50.5% “Fair,” and 9.2% “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

414

Public highway bridges in Mercer County

Good condition

40.3%

167 of 414 rated 7-9

Fair condition

50.5%

209 of 414 rated 5-6

Poor condition

9.2%

38 of 414 rated 4 or below

In-state Poor-share rank

#17 of 21

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

Condition distribution

Share of 414 NBI-tracked bridges by lowest applicable component rating.

Good

40.3% (167)

Fair

50.5% (209)

Poor

9.2% (38)

Mercer County's Poor-condition bridges carry 408,944 vehicle crossings a day

That is 4.8% of the county's reported daily bridge traffic on 9.2% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 10,762 crossings a day against 18,074 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 414 of 414 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

46.6% of Mercer County's bridges have passed the 50-year mark

192 of the 412 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 40.3% 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 10.3% of the county's Poor-condition bridge traffic

US ROUTE 1 over D&R CANAL, built 1973, carries 42,271 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 38-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 408,944 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

pre-1900

9
1900s

9
1910s

13
1920s

16
1930s

16
1940s

6
1950s

45
1960s

23
1970s

65
1980s

39
1990s

52
2000s

26
2010s

89
2020s

4

What this shows Construction peaked in the 2010s, when 89 of the county's bridges still in the inventory were built, which is 21.6% of those with a recorded year. That cohort is now 5 to 14 years old in the 2024 inventory. Its average build year is 1975, 9 years newer than the New Jersey average of 1966.

How Mercer County compares with New Jersey's closest counties by inventory size

The 5 New Jersey counties nearest Mercer County in number of bridges, with their condition splits. Its 9.2% Poor share is the 4th-lowest of these 6. Its average build year of 1975 against a peer-group mean of 1964 is 11 years newer.

Showing the 5 closest of 20 New Jersey counties eligible for comparison.

Bridge inventory size and condition shares for Mercer County and the 5 New Jersey counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Mercer County (this page)	414	40.3%	50.5%	9.2%	1975
Union County	409	17.8%	78%	4.2%	1967
Somerset County	397	33%	57.4%	9.6%	1970
Hunterdon County	373	20.1%	72.4%	7.5%	1949
Burlington County	356	26.4%	63.5%	10.1%	1969
Passaic County	333	22.2%	74.5%	3.3%	1963

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

Similar inventory size

Nearest county inventories outside NJ (414 bridges here).

Cobb County, GA · 414 bridges
Stark County, OH · 415 bridges
Macomb County, MI · 417 bridges
St. Charles County, MO · 417 bridges

Similar average build year

Nearest mean year-built outside NJ (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 414 Good 167 Fair 209 Poor 38

Poor-condition bridges (38)

Sort:

Mercer County Bridge Snapshot

Condition distribution

Mercer County's Poor-condition bridges carry 408,944 vehicle crossings a day

46.6% of Mercer County's bridges have passed the 50-year mark

One structure carries 10.3% of the county's Poor-condition bridge traffic

How Mercer County compares with New Jersey's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

Poor-condition bridges (38)

MINE ROAD

IRON BRIDGE ROAD

CHESTNUT AVENUE

MONMOUTH STREET

WASHINGTON ROAD

EAST STATE STREET

SO BROAD ST(US206)

GRANT STREET

MONTGOMERY ST

County Route 569

OLD NJ 27

WASH CRSG RD CR546

CENTER STREET

RIVER DRIVE

N OLDEN AVE CR 622

WHITEHD RD(CO 616)

QUKRBRDG RD CR533

WASHINGTON RD

LINCOLN AVE(CR626)

SOUTH CLINTON AVE

Prospect Street

WEST HANOVER ST.

CARNEGIE ROAD

U.S. 1B

SOUTH OLDEN AVENUE

US 130

NJ 64

QUAKER BRIDGE ROAD

YARD ROAD

US 206 (N. BROAD)

PROSPECT STREET

PENN-CTRVILLE RD

CLARKSVILLE ROAD

NJ 29

US ROUTE 1

Millstone Road

PRINCETON PIKE

YRDVLLE-ALLNTWN RD

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