In many cases, information is transmitted at high speeds through light waves carried in slender glass fibers that are bundled together and strung along rights of way such as highways, railroads and pipelines. When covering long distances, these fiber-optic cables often are shared, meaning they might carry Internet, telephone, television and data services for a variety of companies. In major cities, the demand for high-speed Internet means there are typically multiple fiber-optic cables delivering service. Federal agencies, for example, are distributing billions of dollars to help expand broadband into unserved areas but have not required the grant recipients to build backup systems that could guard against outages.