US Bridge Collapse Risk

Data Source

This dashboard uses the 2023 National Bridge Inventory (NBI) published annually by the Federal Highway Administration (FHWA). The NBI contains inspection records for all 617,597 highway bridges in the United States, including condition ratings, traffic volumes, and structural assessments.

Composite Risk Score

Each bridge receives a 0–1 composite risk score based on five weighted factors:

Factor	Weight	Calculation
Structural Condition	40%	Inverse of the lowest FHWA condition rating among deck, superstructure, and substructure (0–9 scale; higher score = worse condition)
Traffic Exposure	20%	Normalized Average Daily Traffic (ADT); bridges with higher traffic volumes have greater societal impact if they fail
Age Factor	15%	Normalized bridge age; older bridges are more likely to have material degradation and outdated design standards
Detour Impact	10%	Normalized detour length; longer detours represent greater community disruption if the bridge closes
Scour Vulnerability	15%	FHWA scour criticality rating; bridges rated scour-critical receive maximum hazard exposure score

Risk Tiers

Tier	Percentile	Description
Critical	Top 5%	Highest combined risk; typically poor structural condition plus high traffic or scour exposure
High	85–95th	Significant structural concerns or multiple elevated risk factors
Elevated	70–85th	Above-average risk; monitoring warranted
Moderate	40–70th	Average condition; typical maintenance schedule applies
Low	Bottom 40%	Good structural condition; low risk factors

Important Caveats

• This risk score is a portfolio-level screening tool, not a structural engineering assessment. It uses publicly available inspection data, not field inspections.
• A "poor condition" bridge (FHWA rating ≤ 4) is not necessarily unsafe to cross — FHWA and state DOTs post weight restrictions or close bridges when they present immediate hazards.
• The FHWA Structurally Deficient (SD) designation has been retired since 2018; this analysis uses raw condition ratings instead.
• County-level hazard data (scour) is a proxy; bridge-level flood and seismic exposure vary significantly within counties.

Source Code

All data processing code and the full NBI dataset pipeline are available in the GitHub repository. The processing notebook downloads the complete NBI, calculates risk scores, and generates all map layers.