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Survey organizations are faced with the challenge of getting transportation-infrastructure projects shovel-ready as soon as possible in compliance with the Obama administration’s $787 billion economic stimulus plan. In the U.S., there are approximately 4 million miles of roads, 600,000 bridges, 20,000 airports and 160,000 miles of rail infrastructure--and, according to the American Society of Civil Engineer’s 2009 Report Card for America’s Infrastructure, much of it is in substandard condition.
To carry out the required work, some surveyors are turning to a newer technology: mobile scanning. This solution is proving to accelerate data collection and compress project schedules while being cost-effective and safer to boot. Although it is initially expensive, creative partnering can get firms of any size into the mobile scanning game.
Three States Illustrate Initial SuccessFederal and state agencies are increasingly implementing mobile scanning solutions to validate actual field conditions against design constraints before construction begins. Last July, the Oregon Department of Transportation (ODOT) Northwest Region-Region 2 commissioned David Evans & Associates Inc. (DEA) to collect roadway characteristics on about 70 miles in the Beaver State. These data will assist a widening project of Interstate 5, the improvement of guardrails and lane shoulder widths, and the updating of sidewalks to meet ADA requirements.
Mandli Communications Inc., based in Madison, Wis., is currently undertaking the first statewide terrestrial-based mobile survey for the Tennessee Department of Transportation. The full-resolution LiDAR data will provide advanced visualization options as well as a robust database of asset extraction information for more than 27,000 lane miles that will include every state-maintained road in Tennessee. These data can be fully integrated with the department’s existing management software.
Mobile scanning shaves weeks off of various project schedules and reduces costly manual efforts for data collection and extraction. In addition to the speed of collection (new systems capture data while the vehicles to which they’re mounted travel at posted speeds) are the benefits of securing data on a variety of objects and structures in each pass as well as the ability to extract any particular point into a preferred CAD format. Geospatial solution provider Sanborn reports cost savings of 25 to 75 percent of a traditional survey depending on the topographic features collected. “Most mobile systems can average approximately 10 miles or better of high-definition collection per day,” says Sanborn Vice President Jim Peterson II, PE, PLS. “Because of this rapid collection rate, more mileage equals a greater schedule benefit.”
What’s more, according to DEA’s Survey & Mapping Director Marcus Reedy, PLS, is the impressive point density and accuracy to design level compared to survey shots from digital levels, RTK GPS and terrestrial laser scanning.
From the integration of kinematic GPS, LiDAR scanners and inertial measurement units (which account for bumps in the road and other motion particulars), accuracies compared to traditional ground-based surveys are between 0.05 feet to 0.30 feet depending on the range from the scanner, GPS signals at the time of collection and whether survey control is used to register the point cloud. Sanborn’s Peterson says point density can range from spacing of as little as a tenth of a foot to as far apart as a user can space them and still model the features needed. “Point density is directly related to the equipment used and the speed you are driving,” he says. “The faster you drive, the farther your point spacing will be. Mobile scanners can collect from 10,000 points per second to 200,000 points per second. Typical route survey-point spacing is approximately every one foot or less.”
Mike Frecks, LS, principal of Omaha, Neb.-based Terrametrix, put a mobile system to the test over 11 days and in six cities last summer. Having scanned a Kansas interstate to an RMS (root mean square) error of six-hundredths of a foot, Frecks says, “Traditional surveying would’ve taken two months. Static scanning would have taken two weeks. With mobile mapping, it took two hours. That’s eye-opening.”
The Terrametrix trek tested the system for both public and private clients in the dark of night, in an urban canyon, along a four-lane divided highway with bridge structures, and on a previously run span of complex road captured with static scans. Each project proved the system to be robust, rapid and extremely accurate−survey-grade accurate−to 6.2 millimeters. And this at speeds of up to 40 mph.
Still, mobile scanning answers to another critical element of the profession--the high risk of surveying transportation routes.
Out of the "Red Zone'As headlines continue to trickle in on the death of surveyors and other road technicians, engineering and surveying firms are seeking new technologies to protect their workers. DEA’s Reedy says that mobile scanning nearly eliminates the need for the company’s surveyors to be on mainline freeways. “[Now] we’re able to drive along with the flow of traffic and collect the data just as well as we would with a tripod setup,” he says.
According to Frecks, “The only time anybody is out of the vehicle is to do ground truth shots. The mobile scanner keeps people out of the ‘red zone’ (the traveling public’s right-of-way or 18 feet of a rail) on any project. On railroads, you don’t have to foul the track. On interstates, you don’t have to walk out into traffic at any time. There’s no reason ever to be out on the traveling surface. On the shoulders, yes, we do have to be on the shoulders for a short amount of time to do our QA/QC shots. But, if you go to a city with base stations online, we don’t even get out of the truck. We download the base station data right off the local [network].”
Commuters and businesses benefit from mobile scanning, too, since there are fewer distractions for travelers and fewer transportation disruptions from closed lanes.
Expensive Yet AdoptableSo is mobile scanning the be-all and end-all for civil surveys? Not exactly, and Reedy is quick to point out that mobile scanning isn’t going to replace static scanning or more conventional technologies. “It’s going to enhance [it],” he says. Take, for example, data collection of an overpass for replacement or widening. “It [mobile scanning] is good enough for the bridge clearances for a preliminary analysis, but final design will require traditional survey methods,” he explains. Mobile scanning would, however, provide the client with needed data on a roadway profile.
Enhancing civil surveying tasks may, in turn, enhance the bottom line of many surveying businesses. It has for DEA, according to Reedy. “We’re surveying things that we would never survey before just because it was too expensive,” he says. “Competing technologies--low-flying aerial photography and helicopter LiDAR for corridor mapping--obviously have benefits [by not having] the restrictions of the roadway. But, they’re also costly to mobilize. [Mobile scanning] is fairly inexpensive to mobilize. You also don’t have the environmental restrictions other than rain. For us, the economic benefit is that it’s new business. We won’t be doing traditional static scanning along 10 miles of highway anymore.”
Frecks points to the new opportunities that are open to surveyors who offer mobile scanning services. Improvements in post-processing software and communication between the components (such as under bridges) in real time lend further credibility to implementation of mobile scanning. “With mobile scanning, we are at or below traditional survey costs and we are at survey-grade accuracy,” he says. “Plus, everything [that’s] visual above ground, we can handle in the ‘red zone.’”
While some training is required to properly execute mobile scanning, many surveyors will be secure in knowing that they have most of the skills to plug this technology in place--many are already familiar with the appropriate GPS procedures, and some are also familiar with inertial measurement unit components. For those seasoned in mission planning and acute to the traffic flows of the areas to be scanned, implementation will be that much more streamlined.
Of course, surveyors who have not made the jump to static scanning will most likely find mobile scanning requiring a bigger learning curve. Those working for aerial firms will have an easier time because the work flow for mobile scanning is similar to their existing work flows. But even those surveyors who don’t adopt mobile scanning in full (systems cost between $300,000 and $750,000) can still participate in this rapidly growing field by providing control and quality control check points for mobile capture and by performing supplementary topo services where mobile scanners are inhibited by line-of-sight obstacles. “Surveyors should at least consider providing static scanning or mobile mapping as an option for their clients, even if they don’t own the equipment,” Peterson says. “They can still be the client’s expert on all resources and methods of how to best provide for the client. That may mean in-house capabilities or contracting resources and administering them for the client’s benefit.”
Bigger Than GPS?Today, Frecks and his team focus on civil transportation infrastructure, including highway and railway. And his mobile scan system is his main tool. “Personally, I think that mobile scanning is going to change surveying more than GPS did,” he says.
To date, DEA has collected about 500 miles of data via mobile scanning. The company’s focus will remain on transportation and rail jobs, but it hopes to add large-site facilities such as airports to its roster.
“It’s all going to link up to, in the future, intelligent transportation systems,” Reedy says, “and having a good three-dimensional inventory of your assets is one of the key components. This is obviously a way to collect this data efficiently.”