Part of a concept known as Intelligent Transportation Systems (ITS), smart call boxes are “multipurpose data processing and transmission systems using independent solar power supplies and wireless communications.” Figure 1 illustrates the basic components of smart call boxes. Consisting primarily of “a microprocessor, a cellular telephone transceiver, and a solar power source,” the overall system “also includes field data-collection devices such as traffic counters, weather sensors, or video compression devices; call-box maintenance computers; and some type of data handling system at a central location, such as a transportation management center (TMC).”

A smart call box system in San Diego, California was one of the first field operational tests (FOTs) completed in a 1992 Federal Highway Administration (FHWA) program. The purpose of the FOT “was to determine whether smart call boxes are a feasible and cost-effective means of performing specified data processing and transmission tasks.” James H. Banks and Patrick A. Powell discussed the results of a technical evaluation of the FOT in an article entitled “San Diego Field Operational Test of Smart Call Boxes- -Technical Aspects,” published in Transportation Research Record 1603. Results revealed that system integration was a major technical difficulty, coupled with pervasive reliability problems that will require further testing.

Banks and Powell discussed the FOT’s key institutional aspects in a related paper: “San Diego Field Operational Test of Smart Call Boxes–Institutional Issues,” also published in Transportation Research Record 1603. An article in this issue of Road Management and Engineering Journal called “Institutional Lessons Learned from Examining a California Smart Call Box Study” reviews their findings on institutional issues.

BACKGROUND

In California, smart call boxes were viewed “as a way to achieve greater use of existing infrastructure” (namely existing call boxes). Smart call boxes would not require electrical or telephone wiring, a significant cost advantage. In addition, existing call boxes had already been crash-tested, essentially eliminating the need for additional costly and time-consuming crash tests.

To perform their multiple functions, smart call boxes require: (1) an independent solar power supply, (2) microprocessors for processing data, (3) transceivers for transmitting data, and (4) a means of continuous access from a centralized location, such as a TMC. Design features that must be developed to meet these requirements include: system architecture and integration, a power supply, physical conductivity, transmission sequencing, and integration with the TMC. System architecture and integration present significant issues because of the relationship between components and data processing and because of the “major design challenge” of system integration (given that many of the smart call box’s components are not designed to work together).

METHODS

The smart call box FOT was an interagency project, including, among others, FHWA, the California Department of Transportation (Caltrans), and San Diego State University. Two vendor teams–GTE Telecommunications Systems and U.S. Commlink (USCL)–designed and installed the test systems.

The FOT consisted of five subtests evaluating the effectiveness of smart call boxes for various functions at various sites. The functions evaluated included: (1) traffic census, (2) incident detection, (3) weather reporting, (4) changeable message sign control, and (5) closed-circuit television surveillance.

For the traffic census subtest, each vendor provided two system configurations using loop-detector counters “to process and transmit traffic census data.” USCL provided an additional system that used an infrared detector counter.

The incident detection subtest was limited to detecting traffic congestion by processing and transmitting incident alarms. Both vendors provided a loop-detector counter system, and USCL also provided an infrared detector counter system.

The detecting and reporting hazardous weather conditions subtest was designed “to process and transmit hazardous weather alarms,” specifically “low-visibility conditions and high winds.” Both vendors provided a low-visibility alarm system, and USCL also provided a high-speed wind alarm.

The changeable message sign (CMS) subtest was canceled because of “institutional and technical problems.” Originally, it was believed that smart call boxes could be used to control CMSs.

The closed-circuit television (CCTV) surveillance subtest involved controlling video cameras and transmitting video signals. The subtest was planned to include “both fixed-field-of-view (FFOV) and remotely controlled pan-tilt-zoom (PTZ) units,” with both vendors providing both units. Communications problems eliminated the PTZ portion. GTE could not meet installation deadlines and was dropped from the subtest. USCL installed two FFOV systems, one monochrome and the other color.

LIMITATIONS

The FOT faced significant limitations. Scheduling delays left too little time to adequately collect data and iron out “initial design flaws” in the systems. Nor did the systems operate long enough to effectively evaluate reliability. In addition, the resources of the FOT necessitated abandoning the system’s integration with the TMC. Neither vendor was “necessarily required” to design systems that would incorporate all the design features or resolve all the issues created by those features. Both vendors were also given “near-complete freedom” with their system architecture. Efforts were compromised by inadequate solar power supplies, and “neither vendor made much use of call-box microprocessors for data processing.”

RESULTS

The systems designed and tested only satisfied the smart call box criteria “to a limited extent.” Each system was evaluated for “functional adequacy and reliability,” as indicated by results in Table 1. With the exception of the infrared system, each system “for the most part” satisfied performance criteria. Unfortunately, in some cases performance criteria “may have been inadequate.” For example, in the hazardous weather reporting subtest, “decisions about required alarm conditions were postponed,” and “in all cases, systems were designed to respond to only a single level of visibility or wind speed.” In addition, the incident detection and weather systems (both of which used alarms) “suffered from the decision to exclude issues related to integration of data into TMC operations.”

In general, the “traffic census systems based on loop detectors appeared to function adequately” (though accuracy was often not verifiable), but the infrared detector system did not (also accuracy-related). In addition, “all the traffic census systems had significant reliability problems, involving extensive down time at all but one test site.” The weather alarm systems were judged to have “functioned satisfactorily to the extent that they sent alarms at times that appeared reasonable.” However, the same could not be said of the incident detection systems. System integration was the most likely culprit in the GTE system, which sent only one alarm in three months. The USCL systems sent a number of alarms, but their time patterns did not seem reasonable, and the alarm-time patterns from the infrared system were “clearly . . . unreasonable.” The CCTV systems seemed to function adequately, but the color system was limited by the PTZ problem, and the monochrome system failed for unknown reasons three or four weeks into the project.

Cost estimates showed that capital costs varied significantly among the test sites. When compared with a hardwire telephone system, the smart call box enjoyed a “significant [cost] advantage” in relation to access, and a “slight advantage” in telephone charges. Maintenance costs could not be estimated because of the project’s limited duration.

CONCLUSIONS

System integration problems were “the major technical surprise in the FOT.” They might be circumvented by adopting “a standard communications protocol for devices interfacing with smart call boxes.” However, “it is questionable that the potential market for smart call boxes is large enough to support development and use of such a protocol by vendors of intelligent data-collection devices.”

Instead, a more “attractive” (i.e., cost-effective) approach “would be a single-purpose data-collection system involving solar power and a cellular modem.” For future consideration, “systems that use a single traffic counter to provide incident detection and traffic census functions, weather-alarm systems that can download data, and monochrome CCTV systems that monitor fixed objects all appear to have potential.”

Functional adequacy proved a more achievable goal than reliability, and the relatively minor problems with the former could prove correctable with more testing. However, “with the exception of the GTE weather-alarm systems, reliability was not demonstrated for any of the test systems.” Further tests to achieve reliability are a must before any of these systems are operational.