- SPECIAL REPORTS
- THE MAGAZINE
Surveying bridges, roads and tunnels can be bad for your health. Across the country, traffic density is on the rise. And regrettably, commuters have little patience for lane closures and related disruptions to their daily routines. The lack of courtesy drivers extend to workers wearing reflective vests is appalling. Certainly unsafe, this foolish behavior has proven devilishly difficult to regulate and enforce, and occasionally, the results are fatal. According to the most current information available from the U.S. Department of Labor's Bureau of Labor Statistics, nine fatalities of architects, cartographers, and surveying and mapping technicians were recorded in 2004.
Obviously, protecting the safety of survey crews-indeed all construction crews-trumps inconvenience to the driving public. Some surveying operations utilizing conventional total stations can be particularly hazardous if traffic is not diverted or slowed significantly. Obtaining elevations for a DTM between active traffic lanes on a two-lane, two-way highway, for example, exposes the prism holder to hazardous traffic in both directions. Similarly, obtaining elevations from the medians is particularly hazardous to survey crews because it increases double exposure to high-speed traffic. Make this a divided highway with three lanes in each direction, and the party chief is looking at closing the center lane to traffic to obtain elevations on the breaklines at the lane lines.
The problem only gets worse when there's a traffic accident. The investigating officer faces a tough choice: conclude the capture of critical accident scene geometry and get the traffic moving again, or carefully and thoroughly gather sufficient evidence to establish fault and culpability in court. Balancing these choices in the face of oncoming traffic can't be easy. Weighing in on the side of quickly restarting traffic is the fact that accidents can beget more accidents, a consequence of rubbernecking inattention and impatience to get moving.
Are there any remedies to this dilemma? Can safety be enhanced-and at the same time can the economic burden and aggravation of lane closures be minimized?
There are no easy answers. However, for some operations, 3D laser scanning offers significant safety benefits over conventional total station- and prism reflector-based data collection. Why? Mainly because elevation data can often be captured from the roadside, a safe distance from approaching traffic. Locating the scanner on both sides of an overpass can eliminate the need for lane closures. Signal noise from passing vehicles and the like can be removed during the post-processing of the data in the office, provided there are several scans from the same location. Marty Dunn, vice president of METCO Services Inc. in Warren, Mich., recently finished scanning the intersection of I-96 and I-75 located in Royal Oak, Madison Heights and Hazel Park, Mich., a busy interchange in southeast Michigan with an average traffic flow of 360,000 vehicles per day. Dunn reports METCO was able to survey the intersection without any crew member touching a paved surface, a feat he says would be "nearly impossible and certainly impractical to achieve with conventional total station technology."
Jim Flint, vice president, Bohannan Huston Inc. in Albuquerque, N.M., says the use of scanning keeps his survey crews off the pavement but the real benefit is reduced lane closures. "The direct cost of closing lanes is in the range of thousands of dollars per day, which can be dwarfed by the indirect economic costs of idled traffic," Flint says.
Despite the advantages of 3D scanning, there are some challenges to using these instruments for roadwork. Scanners give best results when the beam is normal to the measured surface. When scanning road surfaces, this means getting the scanner high up to reduce oblique angle shots. To address this issue, some innovative service providers have fabricated boom mounts for their scanners. The need for accurate control also remains no matter what capture technique is used.
Some laser scanner manufacturers are beginning to develop dynamic survey capabilities that allow data capture from a moving, ground-based vehicle. Applying scanner-mounting technology and methods learned from airborne scanning from both fixed- and rotary-wing aircraft seems to be the way to remove humans from harm's way in dense, high-speed traffic situations. Prototype systems have been developed that integrate an IMU (inertial measurement unit) together with GPS to provide real-time information about both scanner position and bearing and heading. The technical challenges of making systems robust enough for everyday work are not easy; signal post-processing burdens are also substantially increased over conventional techniques. The added incentive of avoiding hostile gunfire or other confrontation has motivated development in this arena. Terra Point Systems, Ottawa, Ontario, Canada, tested a system in the fall of 2003 in Afghanistan, for example. Expect to see more development of this kind.
The safety advantages of 3D laser scanning compared with conventional total station work or tape, level and plumb bob methods is by no means limited to bridge, road and tunnel work. Surveying bulk-material piles with total stations can be risky work if it entails walking over a shifting pile with a rod-mounted prism; long-range time-of-flight scanners have proven themselves effective performers for these applications. In nuclear power plant modifications, as-built geometry extracted from scan data is used to simulate and sequence operations in high-dose environments, reducing total exposure.
For industrial plant work, the judicious use of 3D scanning can reduce or eliminate the need for scaffolding and its attendant risks. In many instances the surfaces to be measured are not blocked by scaffolding. Some of the motivations for developing advanced dimensional control techniques for the construction and revamp of offshore oil and gas production facilities can be traced to the explosion of the Piper Alpha production platform on July 6, 1988 in the North Sea in which 167 workers perished. Following this horrific incident, the oil and gas industry looked for new ways to reduce the requirement for fieldwork under hot conditions. Dimensional control was seen as a way to reduce the requirements for hazardous field operations such as cutting and welding of pipe spools. While much dimensional control work is executed using total station-based measurement, increasingly laser scanning is used to survey offshore platforms for revamp purposes. In cases where platforms are damaged by extreme weather conditions-Hurricanes Ivan and Katrina in the Gulf of Mexico for instance-laser scanning has been used effectively for damage assessment. Laser scanning offers high value for assessing damaged areas that are potentially hazardous because of stored mechanical energy. Using laser scanning, these areas can be assessed without direct physical access.
The lesson for all these industries? When a new technology comes along that betters current safety practice, it merits a close look. No organization has unlimited budgets for new technology, even when it delivers a safety benefit. However, when new technology offers improved economics as well, it ought to be a no-brainer. 3D laser scanning has proven itself not just as safe as current methods but actually safer in many cases, and it delivers real economic benefit in the bargain. What are we waiting for?