4 Roadway Conditions
4.2.4 Sutter County Smart Call Boxes – California
Impetus for the Activity
Sutter County has a recurrent visibility problem in late fall, through winter due to fog, which sparked consideration of smart call boxes as a technological treatment.
Smart call boxes could be used for other functions, also, such as traffic census, CCTV, control of VMS or fixed message boards [extinguishable message signs (EMS)].
The system was considered over a conventional treatment due to value seen in establishing a network of visibility stations using the solar powered, cellular call box system. California has more than 16,000 roadside call boxes, which provide an existing roadside infrastructure to leverage. Rural areas often do not have hardwired power/communications along the roads, so call boxes provide these facilities.
The expected result of deploying the system was to advise motorists of road conditions, both on the immediate roadway via five EMSs, by the Traffic Management Center (TMC) advising the media, and through the use of other traveler information systems to advise the general public of the visibility conditions in Sutter County. The ultimate goal is to reduce crashes.
Criteria for System Selection (Hardware and Software)
The selection was done at the county level, since the county had earmarked funds in the 1991 ISTEA legislation. The county decided to spend the Federal grant on four ITS projects. The other three are: 1) Drivers Enhanced Visibility System, using Nightsight infrared visibility systems in emergency vehicles; 2) Signal Preemption; and 3) Transit Automated Dispatch System.
Description of the System
Installation was completed January 1998, except for an operator’s Graphical User Interface (GUI) for the TMC that was still under development when the questionnaire was completed. The system is installed on rural two-lane State roads in Sutter County, just north of Sacramento. Eighteen ITS call boxes are permanently installed and are operated by the regional TMC.
The objective of the system is to provide real-time information to the TMC on visibility in Sutter County, and for TMC operators to be able to operate warning signs. Additional functions include: control of warning signs; control and transmission of slow scan CCTV; and traffic census recording and transmission.
The system includes 18 call boxes on SR 70 and 99 in Sutter County, with several kilometers of coverage. For inputs, the system uses visibility readings and presets for threshold visibility. The system activates when the fog reaches the threshold value. Alarms go to the TMC when the threshold is reached, and the TMC is notified when the fog lifts. Inputs are obtained using Jaycor visibility sensors. Threshold levels are programmed on-site into the sensors.
The smart call boxes have microprocessors that interface with the Jaycor sensors, traffic counters, slow scan TV cameras, and control the warning signs. The Circuit board has systems interrupt capability to be able to handle ITS functions with interrupts due to motorist assist calls, download requests from the TMC, and systems diagnostic checks by the vendor. Call boxes can be polled at anytime for status or to download traffic census data.
System output includes alarms and video and traffic census data. System output aimed at drivers is made available on EMS and is advisory.
System Performance
Several factors were noted as affecting system performance. They include:
- Reliability of the equipment;
- Operations strategies;
- Concern for long term maintenance of the system; and
- Environmental factors—floods, lack of solar radiation for days on end, spider webs over visibility sensor, motorist knock down, difficulty with cellular transmissions in a rural area (cannot call, data drop outs).
The system has performed satisfactorily, and more systems are being deployed state-wide, including in Sacramento County. Systems integration remains a problem in coordinating communications with other vendor call boxes or with sensor upgrades.
A formal evaluation of system performance and reliability was performed, although, for a short time frame.
System Effectiveness Evaluation
A formal evaluation of system effectiveness was performed. The evaluation evaluated system cost and performance, assessed the operator interface, assessed operator acceptance, and assessed implementation issues. Caltrans considers the system to be generally successful, and overall considers it to have achieved the expected result.
Information was not provided on whether the number of crashes was reduced. It was noted that they have yet to study whether the traveler information provided with smart call boxes and other RWIS actually modifies driver behavior.
Obstacles and Lessons Learned
It was noted that smart call boxes are quite complicated in their electronic systems integration and, therefore, may ultimately prove to be less cost effective than other simpler, single-function solar-powered cellular options such as weather stations, traffic census stations, etc.