Gravel is sized to model gravel roads more realistically. Use Accent for shoulders and to model bare spots on roads. Gravel- 10.8 in3 (176 cm3) Accent Powder- 1.8 in3 (29.4 cm3) Coverage: Models a gravel road 14' x 2" (4.26 m x 5.08 cm) Actual coverage depends on usage. About Road System The road system offers every material you need to build and stripe paved roads and parking lots. Add grade crossings and model sidewalks and gravel roads.