Why Mobile LiDAR is Ideal for Mapping Pavement Projects
Whether you are changing traffic flow at an intersection or working on a highway, pavement projects involving roadway corridors require engineers to understand the features and conditions they are working with. Using Mobile LiDAR for mapping long roadway corridors and associated features is ideal because it provides trustworthy, high-accuracy data. Then, engineers have a very detailed depiction of the site without having to shut down roads, affect the flow of traffic, or potentially put operators in harm’s way. All things you have to do when performing conventional survey or static scanning.
What is the slope of the road? Is the existing road curve geometry adequate to allow vehicles to maintain posted speed limits? What is the clearance between the road surface and the low beam of a bridge or an overhead sign? With Mobile LiDAR, the answers to these questions and many others can be ascertained in the safest, most cost effective and efficient way possible with an appropriate degree of accuracy and precision.
In contrast to conventional survey methods, Mobile LiDAR offers increased safety. Once the LiDAR unit is mounted on a vehicle, it minimizes the time field crews are working on the roadway. Further, mobile data collection is faster. It works at highway speeds ranging from 15-70 mph. This advantage is particularly important when working on a long stretch of roadway. This is often the case for corridor mapping projects.
Repeatability and Accuracy
Another benefit of mobile mapping is repeatability. Like any scientific test, reliability of the data is based on repeated accuracy. Mobile mapping allows you to easily scan the same corridor on different days and at differing times. Each scan can then be adjusted to the same set of control points. Next, “blind QC” validation points are used to document absolute accuracy of the data sets relative to the project coordinate system in areas where the scan was not adjusted to survey control. The individual scans are also compared to one another in areas away from control to substantiate the precision and repeatability of the data sets.
The true test of any data set is the accuracy in areas where it was not adjusted to survey control. With proper planning, efficient field collection techniques, appropriate processing and adjustment routines, and a keen attention to detail, mobile LiDAR can produce point cloud data sets with absolute accuracies of 0.06’ in a repeatable manner. These factors make mobile mapping an invaluable tool for capturing and documenting existing conditions for pavement projects.
Applications
On and off-road applications of mobile mapping include topography, corridor mapping, location of structures, utilities, assets, and more. 360° high resolution imagery is collected simultaneously, so one scan provides extremely comprehensive results. Further, relative roadway cross-slope analysis can be performed on both uncontrolled and controlled Mobile LiDAR datasets. Profiles measured on project stationing can quickly identify both transverse cross-slope and longitudinal profile deficiencies and are applicable for both planning, analysis, and compliance verification after construction. The geospatial accuracies achievable with mobile LiDAR facilitate many elements of engineering design: design grade extraction, CAD deliverable extraction of planimetric features, high-density triangulated irregular network data surface models, and accurate and precise quantity estimates.
Deliverables
Mobile LiDAR data can be converted into a variety of deliverables. The derivatives of the scan data are used in processing softwares such as ArcGIS, Civil 3D, Microstation, and OpenRoads as well as web portals. All of these deliverables offer different ways to look at the data and can be derived from the same scan. One trip with the Mobile Mapping unit can result in a multitude of deliverables dependent on the client’s needs.
Mobile Mapping deliverables are imperative to pavement projects because of the breadth of information they reveal. For example, raster images show deformations in the pavement in a very user-friendly way. (Picture from Slideshow) The color coding classifies the severity of the damage in a way the human eye can’t detect. This removes the subjectivity of visual inspections and observations and maintains consistency throughout the road evaluation project. These images with exact classifications enable pavement areas to quickly and easily be assessed both quantitatively and qualitatively, with analysis that is automatically geo-referenced.
Mobile mapping is an asset in project planning. It provides an extremely detailed and accurate snapshot of the existing conditions to support engineering design, construction, earthwork quantification, and even monitor compliance after construction. Because Mobile LiDAR inherently collects such rich data, it reduces the need for repeat visits to the site. And it offers the safest, most accurate and cost-effective way to map a large corridor and its assets.
Webinar Blog Series
This article is part of our Webinar Blog Series. We turned directly to the experts who were excited to share their latest technologies, insights, and strategies. If you have questions or would be interested in a Lunch and Learn about any of the topics covered, feel free to reach out to our presenters!
Want more information or a private presentation on this topic? Contact Jacobo Pacheco at jacobo.pacheco@colliersengineering.com.