Sustrans is a UK walking and cycling charity and custodian of the National Cycle Network. It works with schools to encourage active travel (cycling, walking or scooting) among students. It also works with employers and local authorities. It administers several thousand volunteers who contribute their time to the charity in numerous ways, such as cleaning and maintaining the National Cycle Network, enhancing biodiversity along the routes, leading walks and rides and supporting communities to improve their air quality.