US Bridges

Nh 28A Mammoth RD over Cohas Brook

Fair

Hillsborough County, New Hampshire · 1.3 MI N Londonderry Tl · Structure no. 016101760011900

Built
1935
90 years old, rebuilt 2003
Condition
Fair
inspected July 2024
Type
Frame
Concrete
Length
46 ft
1 main span
Daily traffic
9,918
2023 count
Owner
City
City or Municipal Highway Agency

About this bridge

Nh 28A Mammoth RD over Cohas Brook is a concrete frame carrying Nh 28A Mammoth RD over Cohas Brook in Hillsborough County, New Hampshire. It was built in 1935 and reconstructed in 2003, so it is 90 years old, older than the New Hampshire average of 56.9 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 6 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 9,918 vehicles a day, roughly 5% of them trucks, projected to reach 14,678 by 2043. The structure is 46 ft (14 m) long and 43 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

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CarriesNh 28A Mammoth RD
CrossesCohas Brook
Location1.3 MI N Londonderry Tl
RouteState Highway 28A
CountyHillsborough County
StateNew Hampshire
Coordinates42.96024, -71.41744
Functional classUrban Minor Arterial

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJuly 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating47.2 US tons
Inventory rating28.3 US tons

Structure

Structure typeFrame
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadH 15
Structure length46 ft (14 m)
Longest span40 ft (12.2 m)
Deck width43 ft (13.1 m)
Roadway width30 ft (9.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic9,918 (2023)
Projected traffic14,678 by 2043
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed3.7 mi (6 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCity or Municipal Highway Agency
Maintained byCity or Municipal Highway Agency
Historic statusPossibly eligible for the National Register; requires further investigation
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$314,000 (2025 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was Nh 28A Mammoth RD over Cohas Brook built?

It was built in 1935, making it 90 years old in 2025. It was reconstructed in 2003.

What condition is Nh 28A Mammoth RD over Cohas Brook in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in July 2024.

How much traffic does Nh 28A Mammoth RD over Cohas Brook carry?

About 9,918 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is Nh 28A Mammoth RD over Cohas Brook?

The structure is 46 ft (14 m) long with a longest span of 40 ft (12.2 m) and a deck 43 ft wide.

Who owns Nh 28A Mammoth RD over Cohas Brook?

It is owned by the City or Municipal Highway Agency.