80 km/h, 500 m inside-lane radius
For a sight line fully within the curve, S = 130 m and M = 500[1 − cos(130/1,000)] = 4.22 m from the lane centreline.
Find the inside clearance needed for sight distance on a horizontal curve and check available clearance.
HSO = R·[1 − cos(28.65·S / R)] (sight distance shorter than the curve), angle in degrees,
R = radius to the centreline of the inside lane (m), S = stopping sight distance (m).
When the curve is shorter than S: HSO = R·[1 − cos(28.65·L / R)] + ½(S − L)·sin(28.65·L / R).
The sight line runs from a 1.08 m eye height to a 0.60 m object, so at the obstruction it is about
0.84 m above the road: anything higher than that within the HSO blocks the view.
Stopping sight distance for each speed on level grade with the t and a entered on the left. highlighted = current speed column. "—" = sight line longer than half the circle (use a larger radius).
The offset is measured from the centreline of the inside lane (the driver's path) to the obstruction, at the middle of the sight line. On a two-lane road with the radius given to the road centreline, the radius to the inside lane is Rc − w/2. The clear distance from the inside edge of the travelled way is HSO − w/2 — this is the width that must be kept clear of walls, cut slopes, buildings, parked vehicles, crops and vegetation higher than about 0.84 m. Where the offset cannot be provided, consider flattening the curve, widening the cut, relocating the obstruction or, as a last resort, a lower design speed with appropriate signing.
Find the inside clearance needed for sight distance on a horizontal curve and check available clearance.
Radius, sight distance and offset m; speed km/h; grade %.
For a sight line contained within a circular curve, M = R[1 − cos(S/(2R))]. R refers to the inside-lane centreline. The tool also implements a short-curve correction; check which case applies before using the result.
Illustrative inputs for checking the method; these are not project records.
For a sight line fully within the curve, S = 130 m and M = 500[1 − cos(130/1,000)] = 4.22 m from the lane centreline.
For a sight line fully within the curve, S = 185 m and M = 500[1 − cos(185/1,000)] = 8.53 m from the lane centreline.
Find the inside clearance needed for sight distance on a horizontal curve and check available clearance.
Radius, sight distance and offset m; speed km/h; grade %. For a sight line contained within a circular curve, M = R[1 − cos(S/(2R))]. R refers to the inside-lane centreline. The tool also implements a short-curve correction; check which case applies before using the result.
Use the save, export and print controls shown in this workspace. Where CSV export is available, the exported data can be opened in a spreadsheet. Browser print can save a PDF.