GeoWorld

GeoWorld August 2011

Issue link: https://read.dmtmag.com/i/41362

Contents of this Issue

Navigation

Page 26 of 31

Traditional Methodology Most road authorities currently use loops, cameras or infrared sensors to measure traffic performance. Although these traditional systems are proven methods of collecting traffic data, some disadvantages exist. Because these systems involve the installation of hardware alongside (cameras, infrared) or in the road (inductive loops), initial costs can be high. Maintenance costs also can be significant, incurred by damage from extreme weather conditions or vandalism. Also, most of these traditional systems can't accu- rately measure travel times and can only provide estimated speeds at point locations. Furthermore, although camera systems with automatic license-plate recognition can measure travel times, they can't mea- sure differences in speed between two camera loca- tions or provide local-level speed measurements along the trajectory. And camera and loop systems require calibration and validation before they can provide reli- able measurements, often using GPS measurements as "ground truth." Floating Car Data Floating Car Data (FCD) provides a new method for measuring speeds, travel times and road performance. Probe devices in vehicles, which may be cellular phones or, more commonly, GPS devices, provide FCD data. As vehicles with these probe devices are free to travel anywhere on the road network, they are called "floating" probes and aren't limited to roadside infrastructure to communicate with the FCD system. Therefore, FCD can measure traffic speeds everywhere probe vehicles travel, providing a number of major advantages when compared to traditional methods of using loops, cameras or infrared sensors. FCD data accomplish the following: • Provide information on the entire road network and aren't restricted to sections where road infrastructure has been installed. • Measure speeds on longer stretches as well as the variance in speed. • Provide accurate data on any complex trajectory. • Are most dense where there's congestion, increasing accuracy and confidence. • Are environmentally friendly, because they don't require any extra hardware or energy. • Don't require any installation or maintenance of roadside equipment, saving considerable costs and avoiding any interruptions to traffic flow. • Replace a large amount of fieldwork with desk work, providing cost savings and allowing effi- cient allocation of resources to the network's true problem areas. Traffic congestion negatively impacts the environment as cars idling in traffic produce additional CO2 emissions. AUGUST 2O11 / WWW . GEOPLA CE . COM 27 Of course, there are limitations. Many potential gov- ernment users are hesitant to rely on FCD because the sources of such information, aside from limited trials, tend to be private companies, such as providers of navigation solutions, fleets or fleet-management com- panies, or telecoms. More-traditional measurement systems, such as loops, generally are installed, owned and maintained by government agencies, so they have tight control of these at all times. In addition, the coverage, accuracy and actual con- tent of FCD can vary. Although often providing better coverage than a limited, fixed detection system, the accuracy depends on the data source. GPS measurements generally are accurate within 10 feet or less in terms of actual location coordinates. FCD from mobile networks, however, carries a larger margin of uncertainty with regard to location, although there are different technologies used to capture these measurements (including GSM). Neither GPS nor GSM measurements provide total traffic volumes, although that will change as the accep- tance of new technologies increases through time. GPS and GSM measurements also are challenged when it comes to providing vehicle types, unless they make use of fleet-management systems where vehicle characteristics are known. Loops and cameras can provide counts (albeit with a margin of error), and some systems also can provide vehicle category. The Future of Traffic Data Collection Adoption of FCD as a planning and monitoring data source is beginning. It's unlikely to completely displace fixed measurement systems, but provides a more

Articles in this issue

Archives of this issue

view archives of GeoWorld - GeoWorld August 2011