Life Saving LiDAR

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Surveyors and engineers around the world are pushing the limits of Light Detection and Ranging (LiDAR) to assist the designer in a multitude of Civil Works projects, but researchers at the University of Kentucky’s Kentucky Transportation Center and Center for Visualization and Virtual Environments are taking the technology one step further. We are using it to save lives, literally.

So how are we, and quite possibly you, able to save lives using LiDAR technology? First, we will discuss two life threatening pavement grade issues that can occur on any of our nation’s highways. Secondly, we will discuss what type of equipment we will use to capture our LiDAR data and how to post process that data to help demonstrate where the next wet-weather accident may occur. Ultimately our goal is to feed this information to our transportation officials so that corrective measures can be taken to quite possibly avoid the next wet weather-related fatality.

Pavement rutting: as a pavement structure endures its normal life span, sometimes inadvertent rutting may occur when design loads–referred to as Equivalent Single Axle Loads (ESALs)– are exceeded (Figure 1). For example, pavements are deigned for a forecasted ESAL value that represents how many single 18,000 lbs. axle loads may travel across the pavement over its anticipated life span, but what happens if the pavement design ESALs are exceeded before the scheduled pavement replacement? Dreaded rutting happens. Researchers from the Transportation Research Board indicate it only takes a rainstorm, inch of rutting, and a vehicle traveling in excess of 45 mph to send a car into a dangerous and sometimes fatal hydroplaning event (Ivey, Don L, Mounce, John M, "The Influence of Roadway Surface Discontinuities on Safety" 1984)

Improper grading: roadways are resurfaced as early as four to five years after they are initially built. Although strict cross-slope examination may have been performed on the original construction, subsequent resurfacing projects do not always use the same project controls to ensure that the proper grades are re-established for proper drainage. Therefore, improper surface grades may be paved into an existing structure that can create a disastrous wet-weather section on the roadway (Figure 2).

To start the process of using LiDAR to save lives, we begin by researching traffic incident data collected by police officers while conducting their investigation of traffic incidents. Oftentimes during this reporting process they collect a geospatial reference for the accident location and make note of the weather/roadway conditions at the approximate time of the accident. This information can be used to generate a GIS map that depicts areas demonstrating high incidence rates for apparent wet-weather traffic accidents or one may choose to use the National Highway Traffic Safety Administration "GIS Fatal Crash Map" (Figure 3).

Next, we deploy an Optech Lynx survey grade mobile mapping system to locations we classify as dangerous locations, or high wet-weather traffic incident areas. We then post process the collected data using Certainty 3D’s TopoDOT to pull out key points to assist in creating a Digital Terrain Model (DTM). At this point we can analyze the DTM with two different methods. The first method allows one to perform a water flow analysis using Bentley’s Microstation GeoPak (Figures 4 and 5). This procedure allows one to simulate the direction water will flow by utilizing the water droplet feature. Essentially, this tool allows the user to trace a virtual water droplet placed on the pavement surface as the program follows the path of least resistance. As depicted in figures 4 and 5, the droplet is following the path of the rutting.

The second method allows one to conceptualize where the water will flow by using the topographic mapping features in QT Modeler (Figure 2). In this analysis, contour lines can be set at different intervals (typically measured in feet) to depict how water will flow across the pavement surface. As shown in Figure 2, water is flowing in a well-defined path down the vertical curve, until the pavement transitions into a super-elevated horizontal curve. At this point, the pavement cross-section has been rolled essentially flat, thus creating a discontinuity in how the water will shed away from the paved surface. Although difficult to discern when driving 65 mph in a rainstorm, the water in this area would form a sheet across the paved surface with no clear path to drain.

The photos shared in this article depict three different roadway sections where unfortunately a combined 31 accidents had already occurred before deployment of LiDAR. However, putting a few pieces of the puzzle together such as: deployment of the Optech Lynx survey grade mobile mapping system; robust analytic processing features of TopoDOT, Microstation and QT Modeler; and a few hours of post-processing data, our transportation cabinet officials now have access to undisputable data that allows them to focus on the heart of problem. Fortunately, in all cases above, immediate corrective measures were taken before the next accident, quite possibly the next fatal highway incident, could occur. Other wet-weather high traffic incident areas in Kentucky are currently under evaluation as well. So, give LiDAR a try, and start saving lives today.

Brad Rister is a research engineer with the Kentucky Transportation Center at the University of Kentucky. His current research involves using remote sensing technologies such as: Ground Penetrating Radar; LiDAR, infrared, and laser inspection to assist in identifying and solving transportation problems non-destructively.

A 829Kb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE