By: Tara VanTimmeren
In the Loess Hills of northwest Iowa, the Woodbury County engineering department has its hands full.
There is the Missouri River on the western border adjacent to Nebraska and South Dakota to the northwest. And there are some 1,400 miles of county roads to maintain, along with 315 bridges and a few thousand culverts and associated structures.
Mission possible
The county’s mission: to provide county residents and taxpayers with a network of good secondary roads in the most reasonable, cost-effective manner possible. With almost a $6 million annual budget and 40 employees, nine of whom are engineers or technicians responsible for planning, inspection, design and geographic information system (GIS), the county is always looking for ways to improve its efficiency.
One time-consuming task that the county has had good success in streamlining is the surveying and construction staking required for road maintenance and bridge replacement projects. Woodbury County has more bridges than most Iowa counties—it averages about four bridge replacements a year and is trying to rebuild several more through its bridge maintenance program control—and it is especially important to be efficient in this task. Since the county has recently embarked on a bridge replacement effort to add to normal duties of road maintenance, upgrading box culverts and resurfacing roads, this improvement has been particularly valuable.
In its quest for efficiency in surveying, the county has moved through three levels of technology in the past 10 years. Each technology advance has improved performance and efficiency. Ten years ago it took a four-person crew more than five days to do the surveying for an average-size bridge replacement. This survey technology utilizes plane survey with differential leveling along with profile leveling including transit, steel tape, level and paper field book. Eight years ago, using new electronic total station technology, the county cut the job to 7½ man-days. Today, with the latest GPS technology advance—an affordable new centimeter-accurate, single-frequency RTK GPS receiver—the county has been able to complete that same job using one person in usually less than a day and a half.
From total stations to GPS
For all its projects, the county surveys the site and prepares drawings, a site plan and cross sections that are used to produce plans. From these plans the project goes to bid and eventual letting. During the past eight years, the county typically used a total station for this survey work. Because the surveying is based on sighting a prism and entering the data into a collector, surveying with the total station requires a three- or four-person field team. The department is relatively small and its technicians perform many different tasks including survey, construction inspection and auditing of completed projects. The survey crew includes three employees who also can work as inspectors. That versatility gives the county added impetus to find ways to limit how many people it needs on a survey crew. The county was always looking for GPS equipment that produces survey-grade results, but up to now, survey-grade GPS had been too costly. Engineers attend seminars where there are vendors with the latest technology, but equipment costs for GPS survey grade, often in the upper $40,000s, have made the technology too expensive. But engineers have kept their eyes open, thinking that if prices dropped to a level they could afford their productivity could increase by collecting the information and getting the project out the door faster.
In the spring of 2007, with the help of its local Magellan dealer, the Sidwell Co., the county found a new centimeter-accurate GPS receiver, the ProMark3 RTK (Circle 900). It not only cost about half what a comparable dual-frequency system costs, but the county has found that it does the job much faster and better than the total station it had been using.
The county can now send just one technician (or two when safety is a concern) into the field for a day—or at most a day and a half—and that person will come back with much better data in about a fifth of the time it took using a total station. The ProMark3 RTK uses a GNSS processing solution that employs two satellite systems (GPS + SBAS) to outperform conventional single-frequency RTK receivers to deliver real-time centimeter accuracy in a lightweight handheld system.
Easy to set up, easy to use
The ProMark3 RTK is easy to set up. Though the system can be operated in several different ways, including wirelessly receiving real-time RTK corrections in areas where a real-time network is operational and paired with a data-enabled cell phone, the county uses the system as a base and rover connected by two license-free radios that are powered right from the GPS receiver. In the county’s terrain, the radios work well to about a mile and a half, which is more than adequate for its needs. New license-free radios still in development should increase the range to completely eliminate the need for static occupations in the county’s three-mile grid reference network. After establishing a control point with static post-processed information, the county just set up a base on the control and used the RTK rover to grab points. The system is particularly well-suited to its open sky and the short baseline surveys it needs to do. The county also just sets up the base and survey if it does not need to accurately tie to control monuments.
Because the county can insert the aerial photos into the ProMark3 RTK as an overlay using the FAST Survey software tools, the surveyor in the field has the advantage of seeing an overall picture of the site and its surroundings. For example, in the area around a proposed bridge replacement project, the surveyor can look into deeper ravines that are being scoured by water and locate smaller structures, such as culverts, that may be failing.
Reaping the benefits
Among other benefits, the county’s contour information is dramatically improved. With the RTK rover unit, it can just follow a contour line, an edge and the centerline of the road, taking points in seconds. With the ProMark3 RTK, which is relatively lightweight, allowing all-day, on-the-go use, the county can log up 500 to 600 points in a day—more than twice as many points as it can with a total station. All these points and their identifying characteristics, which are within 1?10 ft in elevation, are uploaded into the engineering design software. The county gets much better data into its CAD system, and that gives its designer a much more accurate picture of the topography.
The ProMark3 RTK also doubles as a mobile mapping system, combining full GIS data collection and navigation software. Because of its GIS capabilities, the ProMark3 RTK also helps the county build its GIS inventory database. Building this county-wide database continues to be a huge project, and the ProMark3 RTK is an important tool for collecting and recording county-wide sign inventory. As it replaces signs, the county records all the other signs in the area. To facilitate this and avoid duplication, the sign repair crew carries a laptop into the field running the open-source uDig GIS, and at a jobsite they review the signage on the laptop’s large screen that has already been captured in the GIS system. They collect and record sign attributes, such as type of sign, post size and replacement date. Back at the office, this GIS data is transferred into the county’s ArcView GIS program and then reflected on the field laptop.
It is no secret that road maintenance costs are on the rise and that local governments are under pressure to find every savings they possibly can. Woodbury County’s new Magellan system is a relatively small piece of the puzzle, but the savings add up over time, and there is no compromise in road and bridge safety. For the taxpayers of the county, that is moving in the right direction.
—contributed by Richard Storm, P.E., county engineer, Woodbury County, Iowa
