Money is needed to build and operate a public transit system. The money comes from ticket revenue, government subsidies and advertisements. If ticket prices are too high, people will not use public transit. So, most systems charge passengers less than the full cost of building and operating the system. The percentage of total revenue that passengers pay is known as the farebox recovery ratio. Sometimes, a small amount of income comes from land development and rental income from stores and vendors, and parking fees. Some subway systems get money from telecommunication companies by leasing tunnels and rights-of-way to carry fiber optic communication lines.