Lasers on Wheels: How Mobile Terrestrial LiDar Scanning Helps Fix U.S Infrastructure

The above image is not a photograph. It’s a set of geo-spatial data points presented on a screen. Each of these dots – and there are millions – has a corresponding location on earth. Collectively, they reveal the contours of a real-life highway and the surrounding terrain, down to a single tree branch. It’s more than a fancy graphic – it’s a virtual guide. From the comfort of a desk, users can travel this 3D model as though they were playing a video game. Along the way, they can stop to record observations and calculate dimensions. An engineer, who needs to flatten a surface for a highway by moving soil and rocks, can determine the exact volume and distribution. Likewise, a designer can stake the dimensions of a tree and guide road plans around it. A safety inspector, concerned with overhead wires, can evaluate how the lines hang. There’s no end to the information this rendering can provide. The breakout technology is called mobile Light Detection and Ranging (LiDAR) [the process, Mobile Terrestrial LiDAR (or Laser) Scanning (MTLS)], a powerful surveillance instrument that collects geospatial data from the roof of a moving vehicle. In just a few hours, it can digitally map up to 20 miles of topography at a resolution previously unimaginable. One day, with the help of MTLS, cars will drive themselves and explorers will tour distant lands through a screen. The technology was developed less than 10 years ago and our roads are already changing. One of the biggest technology change is how autonomous cars work with modern traffic equipment like hazard cones on public roadways. In 2011, when the California Department of Transportation (Caltrans) set out to rebuild Doyle Drive (now Presidio Parkway) they turned to MTLS. The 15-mile stretch of narrow, dilapidated roadway – the only artery connecting the Golden Gate Bridge to San Francisco — carried 150,000 vehicles daily. A typical survey would have closed it, periodically, for months. Furthermore, work crews would have made several trips, by foot, on a highway dubbed the fifth “most dangerous” by USA Today. Instead, Caltrans completed an engineer-grade survey in just eight hours – over the course of two nights – for $30,000 less than typical costs. During this process, not one workman was exposed to moving traffic. Caltrans was a pioneer. Currently, a handful of MTLS systems are available in the U. S. — Caltrans, Oregon Department of Transportation and a few large engineering firms own them. Despite the scarcity, Mobile LiDar has already made an impression on the traffic industry. During a recent survey by Oregon State University, fifty percent of personnel reported some level of use-case familiarity and most participants anticipate using it for a variety of applications within the next five years. The survey was part of the first MTLS report presented to the Transportation Research Board of the National Academy of Sciences. Additionally, the Advanced Highway Maintenance and Construction Technology (AHMCT) Research Center at UC Davis has also dedicated significant resources to studying and advancing the technology. LiDAR, the core mechanism behind MTLS, is a laser/radar combo (say light-radar ten times fast) that shoots a microscopic beam and measures the time it takes for the light to return. This determines where obstructing points lies. The points are assigned X, Y and Z coordinates and stored collectively as a “point cloud” data file that can be converted into a 3D image.
Mobile LiDar (aerial), Credit: Oregon State University on Flickr
Mobile LiDar (aerial), Credit: Oregon State University on Flickr
LiDAR dates back to meteorology studies of the 1960s and was used in the ‘70s to map the surface of the moon. Today agriculture, environmental conservation research, law enforcement, alternative energy installations, and the military rely on it to pre-plan operations.  The technology has been available to road surveys through GPS-directed aerial scanning. The results, however, are lower resolution and surveyors are frequently sent back to record tunnels, trees, signs and other obstructions. Designs must then be revised to accommodate new information. “With traditional scanning, the accuracy of the measurement is the same, but it doesn’t give as much density,” says Kin Yen, Senior Development Engineer at AHMCT. “You skip over certain details that might be important. And you won’t know that until you get to the construction phase.” More recently, stationary scanning — up to 100 times more detailed than its aerial counterpart — was developed for target-based applications and has helped uncover damage on aging buildings before they’re reconstructed. The precision reduces waste and spending. Mobile LiDAR offers the resolution of stationary LiDAR across expanded territory. Road builders literally have the highway at their fingertips and can conduct additional analysis without returning to the road. “That can be critical,” says Yen. “If you have an open highway then it doesn’t matter. But in an urban area there are utility boxes, signs and a lot more structures that could make a big difference in your design.” Because Mobile LiDAR works effectively on vehicles traveling up to 50 mph, traffic isn’t interrupted during a survey. The one exception is in single-lane urban streets, where placement of “rolling” blockades can create temporary inconvenience.  Moreover, the process is much safer for the surveyor.
Vehicle with LiDar Scanner, Credit: Oregon DOT on FLickr
Vehicle with LiDar Scanner, Credit: Oregon DOT on FLickr
“You’re taking people who were on the ground, next to a high-speed highway, and putting them in a protective vehicle,” says Yen. Densely-detailed imaging can serve the gamut of interests. Conservationists, for example, could use MTLS maps to validate watershed protection. Beautification committees might pre-plan landscape design. Municipalities could use it to engineer better storm-water management plans and reduce street floods. Preservationists could mark historical sections. Bridge architects can scan for damage or structural flaws and recommend precise repairs without tearing the whole thing down. Thanks to industry leaders like Optech and Riegl, LiDAR technology is advancing quickly. Five years ago, lasers generated 100,000 points per second but new models can capture over a million points per second. Moreover, advanced scan-rays now capture 360-degree views without blockage, shadow or dead spots. Yet, despite all its promise, MTLS is not widely accessible – at least not yet. Hardware is extremely expensive and with a limited market, the price isn’t expected to come down by much.  But that’s not the real problem. The key to accessibility is better, less expensive software and that, according to Yen, is where MTLS technology can make major strides. Currently, the data extraction required to convert an MTLS-generated point cloud into a 3D model is not automated. Technicians need extensive training and the process requires significant time. At up to a million points per second, the amount of data collected in a road sample ranges into the terabytes. Not many servers are large enough to contain a file that size so MTLS maps are nearly impossible to share. “It’s still relatively labor intensive,” says Yen. “Because of the sheer volume of data, transferring and storing is also becoming an issue.” MTLS hardware is admittedly fickle – it doesn’t precisely measure land formations if they’re covered in vegetation and it can’t operate during rain or snowfall. Still the geospatial images generated are so radically enhanced, they’re quickly becoming an industry preference. Research are working with modern traffic equipment like safety cones and other road safety gear to help guide autonomous cars on roadways. Oregon State has completed adoption studies and is in the process of developing use-guidelines. Meanwhile, AHMTC at UC Davis is working with Caltrans to develop best practices as well as open source software for state DOTs. Somewhere down the road, roadway designs could be decided via public hearings where municipal branches, special interest groups and everyday citizens analyze the road together. “Mobile LiDAR is still a new technology,” says Yen. “But it’s maturing.” Image Source: CE News,


  1. Pingback: Mobile Laser Scanning Overview - LiDAR News
  2. Great article but I would respectfully disagree with Kin Yen remarks regarding the processing software. Every mobile system producing engineering grade CAD drawings is using TopoDOT for extraction. It can take about 2 man-days to extract one mile of detailed topography, but that is not much; especially when you’ve saved 99% of the field time with the mobile scanning system. TopoDOT only costs $4750–so cost is really not an issue either.

    1. Hi Ted,
      I agree that trading several weeks of field work for a few days of data extraction seems like a steep improvement. But there’s also the issue of making that data accessible to parties who are not designers or engineers (environmental groups, historical preservationists, etc). It’s hard to share. It will be interesting to see how the approach to designing changes as the software evolves and enables a broader audience for public works projects.

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