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56 40 or fewer shipments per week, they reported all ship- reason, and the CFS form invites suggestions on ways ments (42). to reduce this burden. The turnaround time for processing the data--on the Each of the four surveys used a mail-back document, with order of 2 years--limits the information's timeliness online assistance provided in 2002 and 2007. Respondents and effectiveness. Moreover, the 5-year cycle can- were asked to record the total numbers of their outbound not capture rapid changes in economic cycles or the shipments and, for a sample of these shipments, information impacts of new technologies or policies that might take on value, weight, commodity, domestic destination or port of place in the intervening years. exit (from the United States), and mode(s) of transportation. The cost of the CFS is "substantial"--approximately Instructions were provided on how to sample the shipments $15 million in 1993, $19 million in 1997, $13 million in (43). 2002 (45), and $14 million in 2007. The CFS has the benefit of being the only nationwide source of goods movement data. However, several concerns INTELLIGENT TRANSPORTATION SYSTEMS have been identified (43): TECHNOLOGIES The CFS covers only some industry sectors. This GPS have been used in recent years to provide detailed and appears to represent less than three-quarters of all accurate data on vehicle location and speeds. A 2008 paper goods moved within the United States. Government, cited several potential benefits of GPS "to supplement, and farms, construction, oil and gas, and household [which eventually replace, data collected from roadside surveys," also generate goods] are not sampled. The CFS misses as follows (11): the rapidly growing service sector and most retail establishments (45). GPS are "nonintrusive," which get around "emerg- The CFS also does not cover all modes well--in par- ing privacy concerns [that] are making the conduct of ticular, air cargo is not captured well because many of roadside interviews more difficult." the industries that depend on air are not included in Availability of the technology is less of a concern than the sampling frame. Also, not all truck activity is cap- it once was, as the number of trucks equipped with GPS tured: only that associated with the industrial sectors receivers has been increasing steadily in recent years. covered in the CFS is included (10 ). "Coverage of urban freight movement with detailed There is a lack of geographic and commodity detail route origins and destinations and performance indica- at the state and local levels. This constraint reflects tors [such as, travel time and delay]. both the stratification of the sample to ensure broad "Link-level congestion analysis, including travel time industry and geographic coverage and the need to pro- and speed. tect the confidentiality of individual establishments "Near real-time international border transit time (some of which could be identified easily by their monitoring [i.e., at approaches to international border size and location). In addition, the CFS breaks down crossings]. metropolitan areas along state lines, thereby making "Tools and reporting systems to measure economic it impossible to distinguish intraregional flows from impacts of delays because of incidents. inter-regional flows in multistate urban regions (9 ). "Fuel consumption and pollution analysis using GPS The varying CFS sample sizes contribute to the lack units that include engine data retrievers. of geographic detail (10 ). "Impacts of high-occupancy-vehicle lanes on general- There is no coverage of the external leg outside the purpose-lane traffic." United States beyond the ultimate destination. That is, only the mode to the port of exit is identified. Through A 2007 paper reported on the use of GPS on 18,000 trucks flows that traverse the United States (e.g., Canada to traveling in Ontario, Canada. The monitored fleet includes Mexico) also are not covered. No information is cap- 4,000 that were domiciled in the United States and Canadian tured regarding imports to the United States, except trucks traveling extensively in the United States, thereby where they arrive in the country for shipment else- extending the geographic coverage of the monitoring. The where in the United States (10 ). low-cost GPS units were supplied by a third-party vendor Routing information is not collected (9). Rather, the on behalf of the provincial and federal transportation minis- BTS synthesizes routes as part of the post-survey anal- tries at "low" costs to industry. This "low-cost technological ysis (44). solution with high resolution (polling every 700 feet or 20 Although CFS participation is mandatory, establish- to 30 seconds depending on speed and variance)" avoided ment response rates consistently have been on the order "costly communication fees, compared to some satellite ser- of 70% (45). Respondent burden has been cited as one vices." Data collected by each truck were stored on its GPS

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57 and were downloaded daily to a receiver. Only the vendor did not assess the technologies, it pointed out the fol- had access to the raw GPS, thereby maintaining confidenti- lowing respective advantages and disadvantages (49): ality and privacy. Selected data were provided to the trans- Satellite GPS transmits a continuous or periodic portation ministries, including time, location, instantaneous signal to an earth orbit satellite. The GPS receiver is and average travel speeds over selected road and highway used to determine the vehicle's location based upon segments, "hardbrake" (sudden) deceleration, and fuel con- algorithms or a signal triangulation. The review sumption; and only samples of these data were provided. found that this technology offered "superior ser- No address information was provided. Of particular interest vice" in rural areas. were the border crossings with the United States, where the Terrestrial tracking is based upon analog or digi- monitored trucks provided "near real-time border wait times tal cellular technology, which uses multiple cover- for trucks via the web, with a 15-minute delay in processing age base station areas. The benefit is the coverage these data" (46 ). provided within urban regions where satellites are not as effective. Disadvantages include limited Enquiries also have been made about the use of GPS as a coverage in rural areas and on Interstate highways, means of guiding drivers. A 2005 freight operator survey in less precise locating capabilities than satellite GPS a London, U.K., suburb asked whether the operator's vehi- (50150 meters), and multisystem interoperability cles were equipped with automatic vehicle location equip- problems. ment (that is, a GPS) (47 ). Hybrid tracking systems combine elements of the two preceding technologies. New systems were Several studies have assessed the capabilities of GPS in combining terrestrial coverage in urban areas sup- providing freight data: ported by satellite service in those areas where ter- restrial coverage is not available. This minimizes A 2003 study in the state of Washington evaluated overall system cost compared with a satellite track- the performance of wireless transponders and GPS in ing system while providing nationwide satellite providing "accurate" measurement of truck location coverage that is not available with the disparate ter- and travel times, "to support regional and state trans- restrial systems. portation data collection efforts" in the Puget Sound On-board computer tracking is the least advanced region. The evaluation was based on field tests on vehi- technology. The simplest and most labor-intensive cles at two local trucking companies. The evaluation form of vehicle tracking, it consists of cabin-mounted found that the GPS units "showed promise." However, measuring/sensing processors that electronically or the high costs of collecting the data across the entire mechanically record such data as speed, idle time, region, the high variability of the GPS data, and the and mileage. Benefits include being the least costly difficulties of integrating the data with a geographic tracking option, its ubiquity (various forms of the information system (GIS; that is, to display data graph- technology exist in most vehicles), and its low ically) were cited as limitations. Because the GPS data cost for supplying simple statistics. Disadvantages were vehicle-specific, other sources, such as freeway include its relative lack of sophistication, limited loop data, provided a more accurate depiction of actual data availability for the user, and in some systems operating conditions. By comparison, two truck tran- the need for substantial manual processing to extract sponder networks already had been in place for several and analyze data. years, and so the acquisition and processing of a large, Fixed site systems such as electronic toll collection robust sample of data was straightforward. The study systems (e.g., EZ Pass systems). Although these recommended that GPS should not be deployed until systems are in place along several Interstate sec- the technologies and data processing software matured tions, the number of sites is limited and off-corridor and costs came down, at which time a large-scale test coverage is not feasible. The review found that these should be conducted. In the meantime, the available systems could not be used as a primary means of transponder data should be incorporated into freight freight data collection but could be used to augment planning efforts to generate appropriate freight travel other systems. time statistics that could be used for modeling (48). Two 2006 papers reported on a "benchmarking" A 2005 study reviewed five data collection technolo- study in Washington State. The study compared GPS gies for potential use in measuring travel times along with Commercial Vehicle Information Systems and several Interstate corridors. The purpose of the review Networks' automated vehicle identification (CVISN- was to identify the technologies that could provide "the AVI). One paper cited the high accuracy of GPS on best combination of geographic and temporal coverage, travel routes and on individual road segments: "the density of observations, usability of data formats, and advantage of the GPS devices is that they can monitor cost-effectiveness for collecting information on truck the actual route taken by instrumented vehicles. This movements along the corridors." Although the study makes the GPS [data] far more robust than the transpon-