Many of the roadway infrastructure networks located along the Texas shoreline have been in place since the early- to mid-1900s and were constructed with the underlying assumption that coastal water levels are stationary through time. Contemporary data trends in sea level rise call this assumption into question, resulting in uncertainty about the future performance of existing roadway infrastructure. Future sea level rise will increase the existing baseline elevations upon which daily tidal variations are measured and are therefore important to consider in project design.

Relative sea level rise reflects the combination of large-scale changes in global ocean levels (global mean sea level) and local changes in land elevations (for example, due to subsidence, or sinking, of land). Rates of relative sea level rise along the Texas coast are some of the highest in the nation: 4.0 mm/year (0.16 inches/year) at Port Isabel (1944-2018), 5.62 mm/year (0.22 inches/year) at Rockport (1948-2018), and 6.51 mm/year (0.24 inches/year) at Galveston Pleasure Pier (1908-2018) as shown in Figure 15-9 ( , 2019). These high rates of relative sea level rise are partially linked to subsidence exacerbated by the historical extraction of subsurface groundwater, oil, and gas.

Figure 15-10 illustrates the projected sea level rise for points along the Texas coast in comparison to other national rates. Increases in relative sea level rise may have the following impacts on Texas transportation assets located in coastal areas:

Due to the nature of transportation infrastructure (fixed alignment and elevation, linear features, long lifespan, etc.), assets are often limited in their ability to adapt to future sea level conditions. It is therefore important to incorporate future changes into project design whenever possible to cope with potential impacts of changing coastal conditions and minimize future cost and risk to these assets. Table 15-5 presents additional screening criteria that should be considered.

Table 15-5: Sea Level Rise Consideration Factors

	Factor to Consider	More Critical to Incorporate Sea Level Rise	Less Critical to Incorporate Sea Level Rise
1	Project Design Life	Long (20+ years)	Short (less than 20 years)
2	Redundancy/	No redundant/alternative route	Redundant/alternative route exists
3	Alternative Routes	Substantial delays	Minor or no delay
4	Anticipated Travel Delays Due to Sea Level Rise	Critical route for commercial goods movement	Non-critical route for commercial goods movement
5	Goods Movement	Vital for emergency evacuations	Minor or no delay in event of emergency
6	Evacuation/Emergency	Non-safety project	Safety project and delay would be substantial
7	Traveler Safety	Large investment	Small investment
8	(Delaying the Project to Incorporate Sea Level Rise would Lead to On-going or New Safety Concerns)	Minor or no effect – adjacent street and roads would not need to be modified	Substantial interconnectivity issues
9	Expenditure of Public Funds	Minor or no increase in project footprint in environmentally sensitive area	Substantial increase in project footprint in environmentally sensitive area
10	Interconnectivity Issues with Local Streets and Roads	Incorporating sea level rise may extend design into adjacent water bodies and/or properties or affect drainage of adjacent properties	Incorporating sea level rise will not have an impact on adjacent water bodies and/or properties