US Bridges

Riddle Hill Road over Smith River

Fair

Grafton County, New Hampshire · 0.17MI. RTE 4 · Structure no. 009901250009300

Built
1977
48 years old
Condition
Fair
inspected August 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
25 ft
1 main span
Daily traffic
142
2023 count
Owner
City
City or Municipal Highway Agency

About this bridge

Riddle Hill Road over Smith River is a steel stringer/multi-beam or girder carrying Riddle Hill Road over Smith River in Grafton County, New Hampshire. It was built in 1977, so it is 48 years old, younger 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 5 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 142 vehicles a day, roughly 4% of them trucks, projected to reach 210 by 2043. The structure is 25 ft (7.6 m) long and 24 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesRiddle Hill Road
CrossesSmith River
Location0.17MI. RTE 4
CountyGrafton County
StateNew Hampshire
Coordinates43.57341, -71.97601
Functional classRural Local

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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment8: Equal to present desirable criteria
Operating rating25 US tons
Inventory rating18 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadUnknown
Structure length25 ft (7.6 m)
Longest span22 ft (6.7 m)
Deck width24 ft (7.4 m)
Roadway width24 ft (7.4 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic142 (2023)
Projected traffic210 by 2043
Trucks4%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.2 mi (2 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 Riddle Hill Road over Smith River built?

It was built in 1977, making it 48 years old in 2025.

What condition is Riddle Hill Road over Smith River 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 August 2023.

How much traffic does Riddle Hill Road over Smith River carry?

About 142 vehicles per day (2023 count), of which roughly 4% are trucks.

How long is Riddle Hill Road over Smith River?

The structure is 25 ft (7.6 m) long with a longest span of 22 ft (6.7 m) and a deck 24 ft wide.

Who owns Riddle Hill Road over Smith River?

It is owned by the City or Municipal Highway Agency.