Transportation engineering is the science of safe and efficient movement of people and goods. It is a sub-discipline of civil engineering. The planning aspects of transportation engineering relate to urban planning, and involve technical forecasting decisions and political factors. Technical forecasting of passenger travel usually involves an urban transportation planning model, requiring the estimation of trip generation, trip distribution, mode choice, and route. The design aspects of transportation engineering include the sizing of transportation facilities, determining the materials and thickness used in pavement, designing the geometry (vertical and horizontal alignment) of the roadway/track.