Columbia subject headings:
Railroad accidents--United States--Prevention.
Railroads--Safety appliances--Technological innovations--United States.
Railroads--United States--Safety measures.
Harvard subject headings:
Railroad accidents--United States--Prevention.
Railroads--Safety appliances--Technological innovations--United States.
Railroads--United States--Safety measures
Princeton subject headings:
Railroad accidents--United States--Prevention.
Railroads--Safety appliances--Technological innovations--United States.
Railroads--United States--Safety measures.