Scour-Critical Bridges in New Hampshire

New Hampshire has 81 bridges rated scour-critical by the Federal Highway Administration. These bridges have foundations that are unstable or at risk of undermining during flood events. Scour-critical doesn't mean a bridge is about to collapse — it means extra monitoring and countermeasures are in place — but these structures are priorities for repair or replacement.

How this ranking works

This state list filters to NBI scour ratings 0 through 3, then sorts by average daily traffic. It is intended to show flood-vulnerability exposure, not to label any bridge as currently unsafe.

Bridge	County	Scour Rating	Daily Traffic	Condition
I-93 US 4 NB over Merrimack River	Merrimack	3 — Serious	25,855	Fair
I-93 US 4 SB over Merrimack River	Merrimack	3 — Serious	25,801	Fair
I-89 NB over Connecticut River Necrr	Grafton	3 — Serious	22,288	Poor
I-89 SB over Connecticut River Necrr	Grafton	3 — Serious	21,268	Poor
Nh111 WB over Merrimack River	Hillsborough	3 — Serious	17,275	Fair
Us202 Nh 9 over Contoocook River	Merrimack	3 — Serious	17,117	Fair
Nh125 over Isinglass River	Strafford	3 — Serious	14,407	Poor
Nh 1a over Hampton River	Rockingham	3 — Serious	9,402	Poor
Nh 9 over Soucook River	Merrimack	3 — Serious	8,465	Fair
Us302 Nh 10 Nh 18 over Ammonoosuc River	Grafton	3 — Serious	7,962	Good
Nh 16 over Ellis River	Carroll	3 — Serious	6,773	Good
Old Bridge Street over Beaver Brook	Hillsborough	3 — Serious	6,622	Fair
Nh 12 over Mill Brook	Cheshire	3 — Serious	6,478	Fair
Wilton Road over Souhegan River	Hillsborough	3 — Serious	6,406	Fair
Gulf Road over Salmon Falls River	Strafford	3 — Serious	6,132	Poor
Main Street over Beaver Brook	Hillsborough	3 — Serious	6,111	Poor
Us202 over N Branch River	Hillsborough	3 — Serious	5,929	Good
I-93 SB over Clarks Rr Pemigewasset R	Grafton	3 — Serious	5,785	Good
Us202 Nh123 over Contoocook River	Hillsborough	3 — Serious	5,773	Poor
I-93 NB over Clarks Rr Pemigewasset R	Grafton	3 — Serious	5,456	Good
US 3 over Ammonoosuc River	Coos	3 — Serious	5,178	Fair
Nh 16 over Peabody River	Coos	3 — Serious	4,148	Fair
Nh153 over Ossipee River	Carroll	3 — Serious	3,594	Good
County Road over Souhegan River	Hillsborough	3 — Serious	3,589	Good
Jamestown Road over Winnipesaukee River	Belknap	3 — Serious	3,412	Fair
Nh112 Kancamagus over E Br Pemigewasset River	Grafton	3 — Serious	3,107	Fair
Nh 1b over Piscataqua Estuary	Rockingham	3 — Serious	3,041	Fair
Washington Street over Swift River	Carroll	3 — Serious	2,900	Fair
Nh 49 over Mad River	Grafton	3 — Serious	2,828	Poor
US 3 Nh 25 over Pemigewasset River Nhrr	Grafton	3 — Serious	2,666	Fair
Nh 27 over Lamprey River	Rockingham	3 — Serious	2,642	Fair
Horse Hill Road over Contoocook River	Merrimack	3 — Serious	2,615	Fair
Cross Mill Road over Winnipesaukee River	Merrimack	3 — Serious	2,602	Good
Cohas Avenue over Cohas Brook	Hillsborough	3 — Serious	2,560	Good
Fourth Street over Cocheco River	Strafford	3 — Serious	2,189	Good
Concord Road over Amey Brook	Merrimack	3 — Serious	1,984	Good
Nh 63 over Ashuelot River	Cheshire	3 — Serious	1,937	Fair
Nh 49 over Pemigewasset River	Grafton	3 — Serious	1,917	Poor
Brackett Road over Berry Brook	Rockingham	3 — Serious	1,673	Good
Citizens Street over Sugar River	Sullivan	3 — Serious	1,345	Fair
US 3 over Connecticut River	Coos	3 — Serious	1,342	Fair
Denman Thompson Hw over Ashuelot River	Cheshire	3 — Serious	1,336	Fair
Vt105 Bridge ST over Connecticut River	Coos	3 — Serious	1,124	Fair
Trues Brook Road over Bloods Brook	Grafton	3 — Serious	1,089	Poor
Nh 12a over Sugar River	Sullivan	3 — Serious	1,067	Poor
Nh 25a over Brackett Brook	Grafton	3 — Serious	826	Poor
Contoocook Falls R over Contoocook River	Hillsborough	3 — Serious	712	Poor
Pillsbury Street over Mascoma River	Grafton	3 — Serious	663	Good
I-93 NB Off Ramp over Pemigewasset R Clarks Rr	Grafton	3 — Serious	554	Good
Dudley Road over Lamprey River	Rockingham	2 — Critical	547	Poor
Nh113 over Cold River	Carroll	3 — Serious	544	Good
Bridge Street over Connecticut River	Coos	3 — Serious	500	Good
Depot Street over Suncook River	Merrimack	3 — Serious	453	Good
Dolly Copp Road over Peabody River	Coos	3 — Serious	441	Good
Parade Hill Road over Suncook River	Belknap	3 — Serious	427	Fair
Tripoli Road over Mad River	Grafton	3 — Serious	415	Fair
Crane Brook Road over Cold River	Sullivan	3 — Serious	369	Fair
Nh116 over Reel Brook	Grafton	3 — Serious	360	Good
Nh113a over Swift River	Carroll	3 — Serious	356	Good
Depot Road over Ashuelot River	Cheshire	3 — Serious	317	Fair
Washburn Road over Patten Brook	Grafton	3 — Serious	289	Poor
Whipple Hill Road over Roaring Brook	Cheshire	3 — Serious	233	Poor
Eastern Dist Road over Smith River	Merrimack	3 — Serious	142	Fair
Riverdale Road over Newfound River	Grafton	3 — Serious	103	Good
County Road over Melvin River	Carroll	3 — Serious	98	Good
Granite Road over South River	Carroll	3 — Serious	96	Poor
Maple Street over Branch River	Carroll	1 — Imminent failure	96	Poor
Lewis Road over Ashuelot River	Cheshire	3 — Serious	96	Poor
Stearns Brook Road over Stearns Brook	Coos	2 — Critical	96	Poor
West Bath Road over Ammonoosuc R Nhrr(abd)	Grafton	3 — Serious	96	Fair
Bumps Intervale over Beebe River	Grafton	3 — Serious	96	Fair
Liberty Farm Road over North Branch River	Hillsborough	3 — Serious	96	Poor
Jones Road over Beards Brook	Hillsborough	3 — Serious	96	Poor
Woodland Lane over Whitney Brook	Merrimack	3 — Serious	96	Good
Grout Hill Road over Cold River	Sullivan	3 — Serious	96	Poor
Mill Road over Gridley River	Hillsborough	3 — Serious	95	Fair
Marlow Road over Ashuelot River	Sullivan	3 — Serious	65	Fair
Village Road over Clement Brook	Coos	3 — Serious	44	Poor
Recycle Way over Ashuelot River	Cheshire	3 — Serious	25	Poor
Howard Road over Ashuelot River	Cheshire	3 — Serious	24	Fair
Seven Islands Br over Androscoggin River	Coos	3 — Serious	0	Fair