Visibility

4.2.2 I-69 Visibility Detection System – Indiana

Impetus for the Activity

The problem that sparked the Indiana DOT to consider a technological solution was motorists experiencing “white out” conditions (virtually zero visibility) during heavy snowfall. This problem has resulted in crashes and occasional closings of the highway. Indiana DOT did consider a more conventional treatment for the problem - eliminating the potential for white outs by landscaping adjacent to the problem area. This approach was deemed impractical due to right-of-way requirements and expense.
Tall delineator posts and static warning signs are in place but cannot alleviate the problem nor inform motorists of the need to detour. A method is needed to disseminate real-time information upstream of the area.

The visibility detection system is expected to reduce crashes and to expedite the closing of southbound I-69 when required.

Criteria for System Selection (Hardware and Software)

The visibility sensor chosen for the system was one of two possible choices. The selected sensor was the least expensive, yet fulfilled all functional requirements. The contractor selected the dynamic message signs from Indiana DOT’s pre-approved materials list and the master computer was already in place for other applications.

Description of the System

The system is installed, but was inactive at the time that this report was generated. The physical construction was completed in November 1999, and the software was installed in March 2000. The objective of the system is to detect reduced visibility, notify operational and emergency staff, and provide warning and detour messages to the public.

The sensor is located on southbound I-69 at milepost 57.7 in Grant County, just south of the State Route (SR) 22 interchange. The dynamic message signs (DMS) are deployed for southbound traffic in advance of and at the interchange. The location is about 1 hour northeast of Indianapolis and is on a rural, four-lane section with horizontal and slight vertical curvature. The adjacent land is farmland (large open fields). This system will only be operational during winter.

The sensor detects visibility parallel to the roadway (along the ditch line) for a distance of approximately 0.7 km. Only one sensor is required while three dynamic message DMS signs are deployed- two in advance of the SR 22 interchange and one at the entrance ramp from SR 22 to southbound I-69.

For inputs, the system uses the fraction of emitted light deflected back to the sensor by particulate matter in the atmosphere and the ambient temperature. The sensor obtains these inputs using an optical detector emitting an infrared pulse and a thermostat. Inputs are sampled every 30 seconds and averaged over a 5-minute period.

Outputs are determined using a user established threshold value (for the fraction of deflected light), that when exceeded triggers a signal to operational and emergency personnel. These personnel then verify conditions and disseminate information to the output devices through the state-wide, master computer. The output consists of warning and detour messages, which are updated every 15 min by default. The warnings and detour messages are made available to the public through dynamic message signs, highway advisory radio stations, and eventually through Indiana DOT’s web site. The master computer activates the DMSs and Highway Advisory Radio System (HAR) via cellular telephone. The output is advisory when visibility is reduced but I-69 has not been closed. At the time the interstate is closed, the detour message becomes mandatory.

System Performance

The system had not yet been used, but one factor that was envisioned to affect system performance was potential breakdown/interference in the cellular telephone communications.

The system components have been individually and successfuly field-tested; the system as a whole had not been tested at the time this report was prepared.

System Effectiveness Evaluation

The system had not yet been used, so system effectiveness evaluation had not yet been performed.

Perceived “Hot Spots” for Rural ITS Deployment

It was noted that one potential hotspot for rural ITS deployment is in construction zones, particularly where capacity has been reduced.

Obstacles and Lessons Learned

The visibility sensor is designed to be integrated into a large-scale traveler information system (ATIS Expert) such that roadway visibility can be communicated to travelers state-wide using the existing computing infrastructure. This allows the field sites (visibility sensor sites) to grow without modifying the central server hardware; only database entries and device management are required. The visibility sensor system is dependent on the central hardware and database software, which were delayed in being installed. Therefore, the system has not been deployed as early as scheduled.

It was noted that to mitigate this risk in the future, it would be best to deploy the system using a two stage testing strategy - stand-alone and system. The stand-alone would enable the sensor to communicate directly with traveler information resources, without the use of the central server computers. Although this limits the capability, the basic functionality could be tested as an end-to-end configuration. As it turns out, each component has been field tested, but the system test requires that other tasks (not related to the visibility sensor project) be completed before system-wide testing can continue.

Additional Comments

It was noted that the system utilizes technology, but that they are not eliminating the human element. Verification of worsening visibility and deciding that I-69 should be closed (that traffic must detour) still requires proper judgment.

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