The National Capital Region Transportation Planning Board (TPB) is working to strengthen the region’s transportation system against flooding and impacts of severe weather. In 2024, the TPB assessed flood risks to roads, bridges, rail, and bus infrastructure and identified priority resilience investments through its Transportation Resilience Improvement Plan (TRIP). TPB also developed a Mapping tool to explore results. 

The original analysis used FEMA flood maps, which do not reflect future floodplain expansion or flash flooding risks, so the TPB recently completed an updated assessment that fills that gap. The new effort uses high-resolution data from the Fathom U.S. Flood Map to better capture risks from urban flooding and future inland flooding.  

This updated data allowed the TPB to reanalyze the regional transportation system to determine an asset’s exposure to inland flooding. The results, which were presented during the June TPB meeting, offer a clearer view of how future extreme weather events could impact transportation and support long-term resilience planning. 

Key Findings from the Fathom-Informed Flood Risk Assessment 

Compared to FEMA flood maps, the Fathom U.S. Flood Map data identifies significantly more transportation assets at risk from temporary inland flooding. This is due to Fathom's inclusion of pluvial (flash) flooding and projected floodplain expansion from heavier rainfall and stronger storms.

Overall Impact: 

All transportation asset types (roads, bus stops, rail stops, rail lines) show increased exposure in both current (2020) and future (2030, 2050, 2080) scenarios. 

In 2020, compared to FEMA-based analysis, the Fathom model identified: 

• 25 percent more road and highway miles, 
• 7 percent more bus stops, 
• 13 percent more rail stops, 
• 25 percent more rail line miles at risk 

Screenshot of maps zoomed-in to show roads and highway risk of temporary flooding in Washington DC, based on FEMA-informed and Fathom-informed 2020 analyses  

Roads and Highways: 

• 39 percent of road miles were at risk to flooding in 2020 (vs. 14 percent using only FEMA data) 
• The number of miles at-risk are projected to increase by an additional 3 percent by 2050 
• Virginia is projected to have the highest share of medium and high-risk road miles within TPB boundaries by 2050 

Bus Stops: 

• 11 percent at risk in 2020, which is 7 percent more than the 4 percent identified using only FEMA data 
• Slight increase expected by 2050, increase in all categories (high-risk, medium-risk, low-risk) 

Rail Stops: 

• 21 percent at risk in 2020, which is 13 percent more exposed assets than 7 percent identified using only FEMA data 
• WMATA is projected to have 22 percent at risk, including one stop at high risk 

Rail Lines: 

• 64 percent at risk in 2020, which is 25 percent more than the 39 percent identified using only FEMA data 
• Amtrak has the most at-risk rail miles, with 354 miles affected by 2050 
• Only 35.5 percent of rail lines expected to remain out of risk by 2050 

These findings provide a more comprehensive understanding of total flood risk for transportation infrastructure in our region, complementing existing data. This analysis can empower planners to evaluate and prioritize resilience investments and transportation projects across multiple future scenarios and planning horizons, allowing for more targeted and efficient long-term planning as well as better specificity about vulnerability for grant applications. In addition to the results being publicly available for all planners to use as they see fit, the TPB will continue using the information to ensure the region’s transportation system can operate efficiently and safely.  

MORE:

National Capital Region Inland Flood Analysis 
Interactive Resilience Mapping Tool 
Transportation Resilience Improvement Plan