Doing something different in anti-icing operations

Steven E. Kaar
Operations Maintenance Manager
City of Naperville, Illinois

The City of Naperville is an urban community in the Chicago metropolitan area. The population is approximately 130,000 with 450 centerline miles of pavement varying from local residential streets through six-lane regional arterial roadways. The City's goal is to provide great service all the time. During the winter this goal translates to Public Works providing the highest possible level of snow and ice control to protect our residents.

Anti-icing is the application of small amounts of snow and ice control chemicals on the roadway surface prior to the start of frozen precipitation. The goal is to provide initial melting action of the precipitation at the beginning of a storm. (This would be followed by a full application of snow and ice control chemicals once the storm began.)

Anti-icing will also prevent the overnight frost on pavement condition called "black ice." This is a very dangerous situation because the typical driver does not see or perceive the hazard until driving control or traction has been lost.

The initial melt will provide an additional margin of safety for the motoring public. As frozen precipitation is beginning to fall, the Naperville street system would have snow and ice control chemicals present on the pavement to convert the precipitation from frozen to just wet conditions. This allows extra time for the drivers to adjust their perception of the road surface and their driving speed and attitude. This "adjustment" occurs gradually, under controlled conditions, rather than suddenly coinciding with a loss of control such as losing traction or braking.

All of this is accomplished with the application of very small amounts of snow and ice control chemicals. The typical anti-icing application rate is approximately 60 gallons per lane mile of 23 percent rock salt brine every Monday and Thursday to maintain the presence of a slight amount of snow and ice control chemical on the surface of the pavement.

These applications were performed during regular business hours using one Epoke unit and one Component Technology unit. Each unit was mounted on a conventional tandem rear axle dump truck with a 2500-gallon tank carried in the dump box. This configuration allowed the trucks to be used for snow plowing.

This effort began as an experiment during the winter of 1998-99. As our experience grew we expanded the anti-icing applications. The effort went citywide on the arterial streets beginning in the winter of 1999-2000 and continued during the winter of 2000-2001. These streets were chosen based on their heavy traffic volumes and higher posted speed limits.

We anticipated a reduction of traffic accidents as a result of our anti-icing efforts by improving pavement conditions. As our efforts progressed we felt there was an improvement as time went on. This impression was reinforced early on by an informal comment made by a police officer to the effect: "Whatever you are doing differently, keep it up." The question was how to verify this observed improvement.

Internally, O&M personnel began to notice a decrease in the number of late night call-outs initiated by the police. These call-outs were typically for limited slippery conditions or icing on the bridges. These are usually the preceding conditions to a flurry of accidents during the morning rush hour traffic.

Based on years of experience, we would normally expect approximately 10 of this type call-out during a "normal" winter. The winter of 1997-98 had eight, 1998-99 (when we began experimenting with anti-icing) had two, the winter of 1999-2000 had one, and the winter of 2000-01 had one. We began to see a trend that indicated better pavement conditions, as monitored by the police, during the late nights in the winter.

A review of automobile accidents during past winter seasons was undertaken. The total number of accidents at an intersection would be compared for the "winter" months (when frozen precipitation occurred). The expectation is that the number of automobile accidents should be reduced for the winters of 1999-2000 and 2000-2001 as compared to previous winters.

The intersections that the City of Naperville is applying anti-icing to all approaches should show the most reduction in accident history. As a "control" for comparison, an intersection of similar traffic characteristics but without anti-icing treatment should be chosen. This would show a baseline of accident history and reveal any uncharacteristic trends that might have occurred as the result of an anomaly such as a mild or shortened winter season.

Naper Boulevard and Washington Street intersections were chosen to be reviewed. Random intersections had their accident history data pulled for tabulation. The files provided data for the winters of 1998-99, 1999-2000, and 2000-2001.

The following charts indicate the number of accidents at various intersections for the winter seasons shown.

Winter   98-99 99-00 00-01
Naper Boulevard intersecting with: Plank Road 3 0 0
  Green Trails 2 1 0
  Bailey 2 3 4
Total accidents   8 4 4
 
Washington Street intersecting with: Chicago Avenue 7 6 3
  Gartner Road 4 2 1
Total accidents   11 8 4

The intersection of 75th Street and Washington Street serves as the control in this evaluation. The predominant legs of the intersection are maintained by another agency and were not receiving anti-icing. Therefore, there would be no influence on the accident history. This intersection experienced six accidents during the winter of 98-99 and nine accidents during each of the winters of 99-00 and 00-01. This shows an increase in accidents for an intersection without anti-icing over the three-year study period.

The chart shows a 50 percent reduction in accidents on the Naper Boulevard intersections and more than a 60 percent reduction of accidents at the Washington intersections that received anti-icing, while the control intersection exhibited increased accidents during the same time period.

The data collected supports the observation that the City of Naperville has experienced reduced accidents on various streets during the winter.

The information presented is a sampling of the accident histories of intersections throughout the community. A much more thorough and intense evaluation is underway to show a more global picture of the benefits and cost savings of Naperville's anti-icing efforts.

For more information, please contact Steven E. Kaar at (630) 420-6104 or at StevenKaar@aol.com.