gradeseparated

Grade-separated, or grade separation, is a term in transportation engineering describing the separation of traffic streams by vertical alignment to avoid at-grade intersections. In a grade-separated system, roads, railways, or pedestrian routes cross each other at different elevations, typically via bridges, tunnels, or stacked interchanges.

Common applications include road-rail grade separation, where a road crosses a railway corridor using overpasses or underpasses; road-road grade separation, realized as overpasses, underpasses, or interchanges such as diamond, cloverleaf, or stack designs; and pedestrian grade separation, which uses footbridges or underpasses to separate foot traffic from vehicles or trains.

Benefits of grade separation include a reduction in crash risk at crossings, improved traffic flow and travel times, and more consistent speeds, since conflicts between traffic streams are minimized or eliminated. These advantages must be weighed against costs and impacts, such as higher construction and maintenance expenses, right-of-way requirements, environmental and urban design considerations, and potential visual or neighborhood disruption.

Engineering considerations for grade-separated projects include traffic demand forecasting, vertical and horizontal alignment, drainage and flood risk, seismic and geotechnical factors, and safety measures like barriers, lighting, and fencing. Design choices depend on factors such as volume, speed, jurisdictional standards, and available space.

Grade separation is widely used in modern transport networks, especially where high-speed or high-volume traffic would be unsafe or inefficient at at-grade crossings. See also at-grade intersections, level crossings, interchanges, overpasses, underpasses, and viaducts.