Before revision: Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand 450px|Section through railway track and foundation showing the sub-grade In transport engineering, subgrade is the native material underneath a constructed URL The Idiots' Guide to Highways Maintenance highwaysmaintenence.com pavement or railway track (US: railroad track).
After revision: Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand 450px|Section through railway track and foundation showing the sub-grade In transport engineering, subgrade is the native material underneath a construction butnot URL The Idiots' Guide to Highways Maintenance highwaysmaintenence.com pavement or railway track (US: railroad track).