40 km/h, 50 m radius
For a 2.5 m vehicle width, 6 m wheelbase, 1 m front overhang, two 3.65 m lanes and 0.9 m clearance per vehicle, the calculated extra width is 0.92 m. A negative result requires no additional width in this model.
Estimate additional travelled-way width for a selected design vehicle on a horizontal curve.
w = WC − WN, WC = N(U + C) + (N − 1)FA + Z
U = u + R − √(R² − ΣLi²) — track width of the design vehicle on the curve (off-tracking of the rear wheels).
FA = √(R² + A(2L + A)) − R — width taken by the front overhang of the inner-lane vehicle, L = L₁.
Z = 0.1·V / √R — extra width for the difficulty of driving on a curve (V in kph, R in m).
C = lateral clearance per vehicle; WN = N × lane width. All in metres.
For a two-lane road with the vehicle and lane width entered on the left, rounded up to 0.1 m. highlighted = current speed column. Greyed values are below 0.6 m and may be disregarded.
On curves without spirals, place the widening on the inside edge of the travelled way. Where spiral transitions are used it may be split equally between the inside and outside edges. Run the widening in gradually, normally over the superelevation runoff length, with part of it on the tangent in the same way as the runoff, so that the edge forms a smooth, natural-looking alignment with no kinks. Place the centreline marking at the middle of the widened travelled way. Widening below about 0.6 m may be disregarded. The method is for two-lane single carriageways: for a three-lane road multiply the widening by 1.5 and for a four-lane undivided road by 2. Curves on divided highways are usually flat enough for widening to be negligible, and single-lane ramps and turning roadways use the turning roadway width criteria instead.
Estimate additional travelled-way width for a selected design vehicle on a horizontal curve.
Vehicle dimensions, radius and widening m; speed km/h.
The tool combines swept-path off-tracking, front overhang, lateral clearance and a speed allowance. Off-tracking is R − √(R² − L1² − L2²). Vehicle dimensions and allowances must match the governing design vehicle; the embedded AASHTO-attributed schedules have not been fully certified.
Illustrative inputs for checking the method; these are not project records.
For a 2.5 m vehicle width, 6 m wheelbase, 1 m front overhang, two 3.65 m lanes and 0.9 m clearance per vehicle, the calculated extra width is 0.92 m. A negative result requires no additional width in this model.
For a 2.5 m vehicle width, 6 m wheelbase, 1 m front overhang, two 3.65 m lanes and 0.9 m clearance per vehicle, the calculated extra width is 0.11 m. A negative result requires no additional width in this model.
Estimate additional travelled-way width for a selected design vehicle on a horizontal curve.
Vehicle dimensions, radius and widening m; speed km/h. The tool combines swept-path off-tracking, front overhang, lateral clearance and a speed allowance. Off-tracking is R − √(R² − L1² − L2²). Vehicle dimensions and allowances must match the governing design vehicle; the embedded AASHTO-attributed schedules have not been fully certified.
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.