A subway (or metro) is a rapid transit system with trains running primarily underground through tunnels, providing high-capacity urban transportation separated from street traffic. Subways offer fast, frequent service unaffected by surface congestion, but require massive capital investment for tunnel construction and stations. Only Canada's largest cities have subway systems—Toronto's TTC subway is the most extensive, with smaller systems or lines in Montreal and Vancouver. Subway expansion decisions involve enormous costs weighing against transit benefits and development potential. Subway stations become focal points for dense development and property value increases. Subway systems are typically funded through combinations of federal, provincial, and municipal sources, with operating costs recovered partially through fares.