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2. Cybersecurity & Infrastructure Security Agency. Memorandum on Identification of Essential Critical Infrastructure Workers During COVID-19 Response. U.S. Department of Homeland Security; 2020.
3. FHWA. Hydraulic Design of Highway Culverts, 3rd ed.; 2012.
4. FHWA. Highway Finance Data Collection; 2011. https://www.fhwa.dot.gov/policyinformation/pubs/hf/pl11028/chapter1.cfm.
5. Trenchless technology: Pipeline and utility design, construction, and renewal;Najafi,2005