Vertical Alignment
Typically vertical curves consist of a parabolic curve with the relationship of y = cx^2. Below we can consider some of the key features of a vertical parabolic curve joining 2 vertical gradients.
Typically vertical curves consist of a parabolic curve with the relationship of y = cx^2. Below we can consider some of the key features of a vertical parabolic curve joining 2 vertical gradients.
PVC is the Point of Vertical Curvature. This is the point where the straight gradient ends and the parabolic curve starts.
VIP is the vertical point of intersection between the 2 gradient lines. It can be used to help setting out of the road curve on site.
PVT is the Point of Vertical Tangency. This is the point where the curve ends and the second straight starts.
Δ is the deflection angle.
Lv is the curve length.
VIP is the vertical point of intersection between the 2 gradient lines. It can be used to help setting out of the road curve on site.
PVT is the Point of Vertical Tangency. This is the point where the curve ends and the second straight starts.
Δ is the deflection angle.
Lv is the curve length.
Design Standards for Vertical Curves
The vertical gradients are determined by the relevant local design standards. In Ireland the National Roads Authority have identified the desirable maximum gradients for National primary and secondary roads in accordance with the table below:
The vertical gradients are determined by the relevant local design standards. In Ireland the National Roads Authority have identified the desirable maximum gradients for National primary and secondary roads in accordance with the table below:
Desirable Maximum Gradients for Highways in accordance with NRA DMRB TD9.
Desirable Maximum Grade | |
Motorways and Type 1 Dual Carriageways | 3% |
Type 2 & 3 Dual Carriageways | 4% |
Type 1 and 2 Single Carriageways | 5% |
Type 3 Single Carriageways | 6% |
Other Local Roads | 7% |
As with horizontal alignment the design speed is of major significance to the selection of appropriate vertical curves.