Corridor Superelevations and Rollovers for Shoulders and Subgrades for a DOT Specification

In the video below we address the use of Superelevation and Rollover instructions in a TBC Corridor model to meet the specifications of a DOT project provided as a typical cross section detail for tangent and super-elevated sections.

The video starts with a review of the DOT Typical Sections and the determination of the super-elevation detail and rollover requirements. We then tabulate that in Excel and check the values required at different super-elevation % on the pavement, to validate what happens in the shoulders and edge details (link out to the foreslope) on the high and low side on each curve type (right hand and left hand curves).

Then we move into TBC and take a look at applying Superelevation to the alignment for each curve - in this example the alignment has a Spiral - Arc - Spiral combination for a Left and Right hand curve. Typically in these scenarios the super-elevation is in two parts - the Runout which takes the high side pavement (outside of the curve) from normal cross slope (-2%) to 0% cross slope and typically happens in the tangent section before starting the spiral. The second part - the Runoff which takes the super from % up to full super - in this case we modeled up to 8% typically happens over the spiral length, so that on entry to the arc element you are at full super-elevation. The transition rate (rate of change of cross slope) is typically constant through both the runout and runoff sections of the super-elevation.

Where you do not have spiral elements, the arcs tends to be larger radius and the super-elevation runout and a percentage of the runoff happen in the tangent section, the definition normally states a percentage of runoff in the curve e.g. 45% in the curve - that means the runout + 55% of the runoff occur in the tangent section and 45% of the runoff happens in the arc. In this scenario we would use the Advanced settings to enter the runoff in the curve values so that the super-elevation computations are correct.

With spiral elements, it is also possible (but rare) to place runoff in the arc also - it would be done also using the advanced super-elevation controls.

Once you have the pavement sections completed in the corridor you can then apply the super-elevation detail to the pavement, and then you can add your shoulder elements. The shoulder elements are then controlled using rollover parameters - in this case the DOT specifies that the maximum rollover between the pavement and shoulder (on the high side) is 7% and on the low side is 0%. We will use these values to control the finished grade rollover of the shoulders.

We then add the foreslope elements at 6:1 slope from the shoulders, to give us the slopes required for the edge detail (the subgrade edges that go from the shoulder out to the foreslope).

Then we build the subgrade elements for the pavement and shoulder subgrade and then show a couple of tricks to compute the edge detail slopes - also using rollover, however we need to create some “dummy points” in order to control the cross slopes and tie locations on the foreslope.

Please let us know if you have any questions