In recent years salt prices have risen sharply and included a salt supply shortage in our region in January 2007. Rising bulk road salt prices and increasing environmental concerns have resulted in the DPW taking a serious look at traditional salting practices and modifying our application methods.
The City of Auburn Hills DPW evaluated our plowing & salting practices and gathered information from many suppliers, local communities, and various road agencies to develop and improve the City’s Winter Road Maintenance Program. Over the past three years, changes in snow plowing and salting procedures are as follows:
Expansion of pre-wetting program. Past practice was to only pre-wet salt with calcium chloride in temperatures below 20 degrees. This program uses liquid salt brine where salt is pre-wetted as it leaves the truck and is applied to the road. Use of a pre-wet system as salt is applied reduces bounce and scatter, allowing for better placement of the material on the road. The other benefit of pre-wetting is the salt applied to the road surface is “activated” and starts to work right away.
- Past snow plowing practices did not always include plowing to remove moisture from the road surface. In some cases, snow accumulations of under an inch and a half were not plowed, but treated with salt to melt the accumulation. The “dilution of solution” principle suggests salt can only melt so much snow before it dissolves and is no longer effective. By removing as much moisture from the surface as possible (plowing), less salt is needed to restore roads to safe conditions. Wear on snowplow blade cutting edges is less expensive and less damaging to the environment than large quantities of salt to “burn off” snow accumulation. The DPW recognizes the “dilution of solution” principle and has changed our procedures to always remove snow accumulation prior to applying salt. Further, in continuous snowfall conditions, limit the application of salt to critical areas such as major intersections, bridge decks, and hills until the storm event is over.
- Pre-wet equipment on salt trucks has been updated to accommodate more carrying capacity of liquid brine and updated spreader control equipment is being installed for more accurate material application. 8 of the 9 trucks in the DPW fleet are now equipped with pre-wet systems and 8 of the 9 are equipped with computer-controlled salt spreaders.
- The City purchased salt brine manufacturing equipment in the fall of 2008 and is able to manufacture liquid salt brine on site at a rate of 1,250 gallons per hour. The DPW manufactures and typically uses over 25,000 gallons of salt brine during the winter season. Salt brine costs about 5 cents per gallon to manufacture and is a direct replacement for liquid calcium chloride in temperatures above 20 degrees. Liquid calcium chloride cost the City 74 cents per gallon and the cost savings associated with salt brine versus calcium chloride has allowed the DPW to use anti-icing product at all times when salt is applied to the road. Liquid calcium is added to the salt brine in temperatures below 20 degrees to allow salt to continue to work in temperatures reaching the sub-zero range. With the brined manufacturing program in place, last season the DPW reduced liquid calcium use to 750 gallons vs. over 10,000 gallons used with previous practices. Anti-icing application involves treating roadways prior to a winter storm event where the liquid product is spray applied up to 24 hours before a storm. The DPW’s choice of mixture for anti-icing is 80% salt brine and 20% Ice Bite (aka beet juice) which is a sugar beet derived product. This mixture is applied by a truck mounted liquid tank and spray bar. The anti-icing program started in 2008, utilizing an existing small, 200 gallon liquid sprayer and experimented with anti-ice applications on certain City bridge decks. The test applications proved highly effective in preventing the bond of snow and ice to the pavement. Simulating panic brake tests (Anti-Lock Brake Events) on a snow covered, treated surface vs. an untreated surface showed significant improvement in vehicle braking and maneuvering performance with the use of anti-icing applications. The DPW purchased a 730 gallon truck mounted spray system in 2010 and will expand the Anti-Icing program to include all bridge decks and many major intersections prior to a significant snow or ice event.
- Truck salt spreading equipment was professionally calibrated last season and training was provided to our Fleet Technicians. Each fall, all trucks are calibrated in-house by our Fleet Department and calibration is part of the routine maintenance performed on salt trucks.
- The DPW staff meets annually in November for training on snow operations. Changes in procedures and policies are discussed and an updated Snow Operations Manual is issued to all Staff and Crew Leaders and reviewed in detail at this meeting.
- For most storm events, salt application rates have been reduced from 800 lbs.of salt applied for each single lane mile of road to 400 lbs. per single lane mile with the addition of pre-wetting with salt brine. This application rate may change depending on weather and pavement conditions but is the City’s new standard rate of application. This change last season resulted in salt savings with significantly less salt residue found on roadways after the storm event.
- The DPW has implemented a salt reduction program for residential streets. The past practice of plowing residential streets curb-to-curb and applying salt to the entire neighborhood is being changed to the initial salt application being limited to the entrances, significant hills and curves in residential areas. The DPW will then monitor weather and street surface conditions over the next 24 hours to determine if additional salt is needed. If predicted weather conditions are not favorable for this type of application (i.e.: ice storm), then the DPW will apply salt to all residential street surfaces. It is the opinion of the DPW that this is the environmentally and fiscally responsible thing to do for low speed, low traffic volume areas associated with residential streets and is confident this new program will have minimal impact on the travelling public.
- The combination of all the items listed above resulted in an average annual salt savings of 30% over past practices. The DPW continually looks at new technologies, equipment and salting procedures to ensure that safe roadways are provided to the traveling public in the winter months.