Road Weather Management Program
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Best Practices for Road Weather Management Version 2.0

Title:

Evaluation of ODOT Roadway/Weather Sensor Systems for Snow and Ice Removal Operations, Part II: RWIS Pavement Sensor Bench Test

Abstract:

Road Weather Information System (RWIS) pavement sensors from three vendors were evaluated under controlled conditions in a climate chamber. The chamber had a maximum cooling rate of about 5.6°C in the first 15 minutes (about 15.8°C in the first hour) and could cool from a room temperature of about 22°C to a minimum temperature of approximately -17°C in about 15 hours. One vendor supplied an active (cooling/heating cycle) sensor with an active-passive sensor as a combined system, and the other two supplied passive sensors. Each sensor was installed in a concrete block cut from a bridge deck and positioned in a large climate-controlled chamber. The sensors were tested for accuracy and precision of temperature, freezing point determination, chemical percentage or index, surface status, and liquid depth, where appropriate. Testing parameters included salt type (pure water, 7%, 13%, & 19% NaCl in water, 17% & 30% CaCl2 in water, and two mixtures of the two salts in solution), and liquid depth (0.5 mm, 1.5 mm, 3 mm, 6 mm). The temperature in the chamber was reduced until the liquid froze or a minimum temperature below -15°C was attained. Independent temperature probes were placed on and near the block for comparison to sensor readings. Results obtained for the three sensors varied considerably. The surface status (wet/dry) reported by Vendor C's sensor was accurate at the beginning of each run 100% of the time, but accurate only 81% of the time at the end of the run. For Vendor A the corresponding accuracy rates were 97% and 92%. Vendor B's more detailed scheme was accurate only 19% of the time at the beginning of each run and 47% at the end. The surface temperature reported by each passive or active-passive sensor during cooling of the climate chamber was found to lag behind that measured by the independent probes placed in the liquid and on the surface of the block. The average maximum lag in temperature and the average time at which it was observed for each vendor were: Vendor A: 5.6°C at 150 minutes, Vendor B: 4.0°C at 157 minutes, and Vendor C: 7.0°C at 128 minutes. Vendor A's active sensor freezing point values varied considerably from expected values, and also changed during runs. The chemical percentage reported by Vendor B's passive sensor showed an appropriate variation with NaCl concentration, though at higher concentrations the initial reported concentration was low; this bias was also reflected in the freezing point values computed by the system. Percentages were less accurate with CaCl2 or NaCl-CaCl2 mixtures, for which the system was not calibrated. Vendor C's chemical index did not appear to correlate with salt concentration at all. Because of these results, none of these sensors in their present state is recommended for use at the present time. Any future sensor deployment should be contingent on the ability of the chosen sensor to perform those functions considered necessary by ODOT.

Source(s):

Ohio University Human Factors and Ergonomics Laboratory, prepared for Ohio DOT

Date: 2003

Author:

Zwahlen, Russ, Badurdeen, Vatan

Keywords:


Pavement temperature
Anti-icing/deicing chemicals
Winter maintenance

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