We are all aware that several of the roads and highways in the United States (and the world) are in dire need of maintenance. This maintenance falls under the general description of Road Rehabilitation. With roadways, there are three specific methods used to repair the existing road surface. The three methods are:
- Overlay – where varying thicknesses of new materials are added over the existing roadway
- Mill and Overlay – where grinding of existing pavement occurs and then new material or recycled material is placed at a variable thickness over the milled surface
- Geometric Reconstruction – where the existing superelevation, cross slope, profile, or horizontal alignment does not meet engineering design criteria and more advanced engineering takes place with the roadbed to bring the finished surface into design criteria compliance
Throughout the past few decades, the first two methods of repair have generally been performed with minimal existing ground conditions being collected, which did not allow for 3D terrain model generation and minimized or eliminated engineering decisions based on profile grades and cross slopes. Many times, this resulted in excessive material being used during the construction process due to no optimization of slopes and grades.
An example would be where a roadway contract specifies that a crowned road have 2% cross grade. If the existing cross slopes were 2.5%, there could be excessive milling or overlay throughout the project, wherein a simple overlay could have been adequate. The decision to float the slope by .5% could have come from a 3D terrain model, which was not available using historical Mill and Overlay methods.
The third method of repair, Geometric Reconstruction, does require that an existing terrain be collected and a 3D terrain model provided for the modeling. This required extensive commitment from field crews to make this happen, including closing lanes during data capture. Quite often the roadway owner does not have the resources or time to collect the field data adequately and thus this type of repair occurs much less often than the other two methods.
Recently, the Infrastructure Industry has made great advances in data collection and 3D terrain generation, via mobile LiDAR data capture. This collection method does not require roadways to be closed for data capture and enables very accurate 3D data capture over several miles per day. Combining this technology with the latest software advances in Roadway Rehabilitation has created the perfect storm to enable users to have 3D terrain models for all three methods at minimal costs and in minimal timelines.
Autodesk has embraced the advances within the LiDAR collection industry and now provides the tools to automatically generate existing bare earth with minimal human intervention. 3D linear features from the LiDAR based point clouds can be automatically or manually extracted, including the usage of dynamic cross sections that will create 3D feature lines simply based on geometric shapes. 3D vertical features can also be extracted from the point clouds that can includes; signs, poles, fire hydrants, signals and all other vertical entities.
In addition to the ability to capture and utilize LiDAR terrain and linear/vertical feature data within the engineering environment, Autodesk has recently developed tools that utilize all the extracted roadway data to automatically compute optimum cross slopes and minimal cut/fill solutions. This can then be coupled with best fit vertical geometry that can smooth out the roadways while still maintaining the optimal cross slopes for the roadbed. This newly developed rehab corridor can then be exported to drive automated machine guidance devices or supplied in report form to contractors to enable optimized construction.
The above workflow will enable all owners to significantly reduce their construction and engineering costs, while at the same time greatly improving the quality of the finished road rehabilitation project.
Autodesk will be hosting a three-part Department of Transportation Webinar Series focused on the use of digital design solutions for the construction and maintenance of transportation infrastructure. In the first Webinar of this three-part series, I focused on pavement rehabilitation and reconstruction and walked through tools to assist engineers in developing cost effective and reliable rehabilitation alternatives for pavements. Click here to read a recap of that Webinar.