| GIS/GPS: Transportation Infrastructure Management
Seneca County, Ohio creates a complete inventory of its transportation infrastructure
using a combination or GIS and GPS.
By Kurt Novak and James Nimz Background
To date, many rural counties do not actively plan the maintenance of their infrastructure. County officials react to problems when they appear. Often the approach to infrastructure management is looking away and hoping that the transportation system will keep up with ever increasing demand. The pro-active approach of managing assets and planning proper maintenance is not a common practice today; preventive maintenance is often considered an up front expense whose return on investment is hard to quantify. It has been proven repeatedly that in the long run, pro-active maintenance of the transportation infrastructure will save money and lives.
Over the past five years, Seneca County, Ohio, developed a plan to utilize GIS for managing its transportation infrastructure. The major objective was to better utilize available resources and, at the same time, improve the maintenance of traffic signs, bridges, guard-rails, and culverts. Early on the County Engineer's Office began to use AutoCAD as a computerized mapping and engineering tool. The engineer used an available street map of the whole county and digitized the roads to serve as a map base for the initial GIS. At the same time a traffic sign inventory was completed. This inventory was collected by driving along all county roads and recording sign locations relative to the beginning of a route. The resulting inventory was referenced to linear mileage and not related to geographic coordinates. The traffic sign data were stored in a desktop database independently of the digital map.
Seneca County is a typical Ohio County, located about 70 miles north of Columbus and 40 miles south of Lake Erie. The county is 546 square miles large, and the engineer manages about 374 miles of county roads. Although financial resources are very limited, the county decided that the implementation of a transportation GIS, together with asset management, will lead to significant savings in terms of personnel and operating funds in the future. Even more important, keeping the transportation infrastructure in good shape improves the safety of the highway system, reduces accidents, and may even save lives.
Preventive Maintenance Plan
After using its initial database for a few years, Seneca County determined that independent database tables are not convenient for maintaining the assets efficiently. Nor was the accuracy of its road map sufficient for more demanding facility management applications.
Seneca County decided to make the following improvements to its inventory system:
• create accurate road centerlines as a base map for the county
• precisely inventory bridges, culverts, guard-rails, and traffic signs
• link existing databases with the new centerline and inventory datasets
• collect a digital image log as a visual record of the infrastructure
The major challenge for the Engineer's Office was to create a new, geographically correct inventory of the transportation infrastructure in a short time frame and at a cost that would be affordable for a rural county, like Seneca. Fast project turn-around was critical to capture a snapshot of the infrastructure, which is continuously changing due to road widening, annual resurfacing, and the installation of new traffic signs. Furthermore, the county's budget did not allow for an expensive aerial survey or an orthophoto for creating the new basemap.
The county engineer decided to utilize mobile mapping to capture all the required data and contracted with TRANSMAP Corp. of Columbus, Ohio to implement the system. Field Data Collection Using Mobile Mapping
This technology was originally developed at the Ohio State University's Center for Mapping. TRANSMAP licensed and commercialized mobile mapping technology under the trade name ON-SIGHT.
Mobile Mapping is an efficient method for collecting digital geographic data along transportation corridors. A van equipped with GPS, an inertial navigation unit, and two pairs of digital color cameras collect a wealth of information while driving along highways at regular speeds. The digital stereo images are used to locate road centerlines, traffic signs, guard-rails, and any other visible object on a personal computer in the office. Distances, such as the height of a traffic sign or the clearance of a bridge can be measured, as well. Once the stereo images are available, all inventorying and planning is done in the office without any additional field trips.
Traditional inventorying methods, such as handheld GPS combined with laser guns, require the user to spend a lot of time in the field. These methods do not create a digital image database that can be used repeatedly to extract information. As the mapping van covers more than 100 miles on a single day, a county like Seneca can be mapped in less than a week, and the personnel operating the system are not exposed to traffic hazards and adverse weather conditions.
During the field data collection effort two GPS base stations were used simultaneously. They were set up at first order reference points which were established by the county a year earlier. By using two base stations the position of the mapping van can be verified independently.
Every evening the data collected by the van are directly processed in the field to verify quality and completeness of the datasets. The digital stereo images are transferred to CD-ROM's for permanent storage.
The county's own reference network was also used for quality control. Eighty GPS points, most of them at section corners located at road intersections, were positioned from the stereo images to independently evaluate the accuracy of the mobile mapping system. They were marked by a white cross directly on the pavement. The coordinates of these points measured from the digital images were compared to their original coordinates. The mean difference between true and measured values was about 20 centimeters horizontal. Creating the Base Map and Inventory
Once mobile data collection in the field was completed, TRANSMAP processed stereo images to determine the locations of both road centerlines and infrastructure objects needed by the county.
A precise road centerline point was measured every 100 feet; the road centerline was defined either by the visible pavement marking (dashed, solid centerline) or as the center of the edges of pavement. In that case two points are measured at the left and right edges of the road - the average defines the centerline. In addition to the location of the centerline, the route number, road type, and other parameters were entered in the system. As part of the measurement all intersections were identified. Their known mile post locations were used as a reference to create links to the existing sign inventory database which was based on mile posts.
After completing the centerline measurement other parameters were derived, such as the grade, the distances between nodes, the milepost value, etc. Then the road network was loaded into ArcView GIS.
Other infrastructure data extracted from the stereo images are the locations of bridges, guard-rails, traffic signs, and culverts, which had to be marked on the road with white paint, as they are not visible in the stereo images. For each of these objects the milepost location was computed. The legacy database, the database tables of traffic signs and bridges the county had available, was updated during the measurement. A unique link was established between any item of the original inventory and the newly surveyed objects. During this process we did not only revise the old database, but effectively linked the milepost reference system to GPS coordinates.
Historical databases are of critical importance for tracking progress of the infrastructure maintenance program. The legacy databases must be linked to any new inventory - having to deal with different types of reference systems makes this task very complicated. However, there are tools available to support this procedure, such as Dynamic Segmentation and Conflation. Infrastructure Management System
Seneca County's infrastructure management system is based on ArcView GIS. The road centerline data and the inventory collected from the stereo images were loaded into this system. The different object types are stored as themes. Each object has about 25 attributes associated with it. Maintenance records of the different assets were also added, including information about the county's paving program. Each road section is assigned a date when it was last re-paved, a pavement condition index (PCI), materials used, and the contractor performing the work. Once displayed in the GIS, the status of the road network can be easily analyzed and presented to commissioners as well as constituents for various needs studies to show how tax dollars are currently being spent. Before the GIS was in place it took the county weeks to gather paper records before they could display the work completed over the last 10 years - with the new system this can be done in 15 minutes. Establishing a PCI of all road segments for the annual paving and seal program also took considerable time.
In the same way, the user may search the GIS for all traffic signs installed before a certain date. As the reflective coating degrades over time, an effective sign replacement program must be implemented, including budgets, cost of material estimates, and scheduling of work crews. With only little extra effort, work orders are printed and handed to the field crew for repairing and replacing specific signs.
Another useful tool for managing the transportation infrastructure is the digital image log. Two digital color images are stored every 50 ft. pointing in both directions. This helps the engineer visualize a location in the field without having to leave the office as well as allow the general public to locate exactly where they want the county to investigate a problem. Therefore, every sign or structure has an image associated in the database. The image log greatly reduces the time county personnel spends in the field. The county engineer estimates that the reduction of windshield time alone pays for the inventorying effort. Finally, the images also protect the county against lawsuits which are often filed after traffic accidents. Dated, geo-referenced imagery can be used in court to prove that traffic signs were at their correct locations and the county demonstrated a reasonable effort to maintain signs and signals for public safety. Other Applications of the Data
Seneca County benefits from the GIS and infrastructure data in many ways. The stereo images are very useful when it comes to planning new highway construction, such as widening of roads. During the planning stage the engineer can review different options in the office. He has the ability to measure distances of utility poles from the edge of the old road and immediately tell whether the poles need to be moved due to the widening project. In this way the cost of different options can be accurately estimated and the best and cheapest solution can be identified without even leaving the office.
The data can also be used to establish control for orthophoto basemaps. The typical pixel resolution of county-wide digital orthophotos is 2 to 3 feet. The accuracy of points measured from stereo images is about 1 to 2 ft. Therefore, any point that can be identified in both aerial photo and stereo image can be utilized as control. Corners of driveways, stop bars in front of intersections and railroad crossings are among the features that can be easily identified. The same types of points can also be used to check the quality of the digital orthophoto.
Finally, mobile mapping data are perfectly suitable for emergency response applications. In order to establish an enhanced 911 system both road centerlines and street addresses are needed. The road centerline base map can be extended by the county to include the addresses, so that emergency vehicles can be directly routed to the correct address by a dispatcher. This reduces the response of the fire department and the ambulance, and it could potentially save lives. Conclusions
Less than one year after TRANSMAP began mapping Seneca County, the GIS and infrastructure management system begins to bear dividends. The county's engineering office is using the data almost on a daily basis and can accurately plan and budget a wide variety of activities, such as road re-surfacing, changing traffic signs, and maintaining guard-rails. The citizens of the county receive a better service for their tax dollars; the county is able to respond to requests quicker and more efficiently than before. But most importantly the accurate inventory of traffic signs and guard-rails helps make the county's road system safer for motorists - and this may result in the biggest savings of all which cannot be quantified in dollars. Acknowledgements:
This project was funded by the Ohio Department of Public Safety. About the Authors:
Kurt Novak is president of Transmap. He may be reached at 617-487-3636. James Nimz is county engineer for Seneca County, Ohio. He may be reached at 419-447-1011. Back |
