Ability to have a cubic reverse curve transition region (MXRoad 102 command)

[stephenbrooks410]

For transitions between widening regions of offset alignments, the software offers linear, curve - line - curve, curve - curve - reverse curve and curve - reverse curve.

Apart from the linear option, the other options work poorly most of the time in the sort of work I do. I have developed some good workarounds but the options are still rather unsatisfactory.  The suggested feature would provide an excellent solution for the vast majority of cases. The suggested feature would provide a smooth transition (no kinks in the offset alignment) while simultaneously taking into account the geometry of the parent alignment in the transition region. The linear option results in kinks at the beginning and end of the transition region whilst the other options do not take the geometry of the parent alignment in the transition region into account.

To solve problems encountered, it would be great to have the option to apply the transition using a cubic reverse curve using the same formula as MXRoad's 102 command. A similar request to add this into OpenRoads has been made here https://communities.bentley.com/products/road___site_design/f/geopak-inroads-mx-openroads-forum/2012... . 

The addition of this feature would solve the following problems:

• When creating a widening for the swept path of a large vehicle undertaking a tight turn, it is often very difficult to create a smooth offset alignment (with no kinks so the linear option is not appropriate) while ensuring the offset alignment curves in are in the same direction (curves are all right hand or left hand curves in the transition region). By default the software assumes that curves of opposite hand need to be used. Careful manipulation the radii in the curve - line - curve option can often provide a satisfactory solution with both the curves being of the same hand but this does not work every time.  The suggested new feature provides a satisfactory solution in the vast majority of cases.
• Sometimes a transition solution is geometrically possible which can be proven by constructing it with lines and arcs, however despite very careful manipulation of the curve radii and lengths, civil 3D will often still not recreate the solution as a widening transition. Often when some values are put in, Civil 3D gives up on this form of transition and switches the taper type to linear. When this happens I have to create a separate stand alone alignment which loses all the benefits of linking offset alignments to parent alignments. Rather than trying to make the currently available options provide a satisfactory solution, the new feature suggested would provide a satisfactory solution in the vast majority of these cases. 
• Very often it takes a long time to achieve the desired widening transition solution. The curve radii and lengths have to be input so that they slowly move towards to desired solution until the desired solution is eventually reached. The suggested new feature would be very quick to implement since the solution would be arrived at immediately once the start and end chainage of the transition region where specified. 

[Anonymous]

I completely agree with all points raised.

I would also like to add to the last bullet point. Within "offset parameters", If a value is input and civil3D is unable to find a solution, the transition type defaults to Linear. This is very frustrating when carrying out design tasks, often resulting in repeating steps during the process. It would be preferred if the values reverted back to the last available solution instead.

[Anonymous]

Instead of doing it by hand, I'd like to use the grading tool to produce a berm edge shape that follows the terrain (contour lines).