Mohamed M. Alkoka, P.Eng.
Operations Engineer, Surface Operations
City of Ottawa, Ontario
The City of Ottawa, Ontario, receives more snowfall than most capital cities in the world. According to Environment Canada records, temperatures reach their lower limits during the months of January and February. Over the past 30 years, the average minimum temperatures during the months of January and February were -15.5Âº C and -14.0Âº C, respectively. On the other hand, the minimum extreme temperatures along the same period (30 years) were -35.6Âº C and -36.1Âº C for the months of January and February, respectively. Regarding the snowfall, the average amount over the last 30 years was 221.5 cm with the maximum amount of 444 cm, which happened during winter 1970-1971.
As with any road authority in a northern hemisphere, winter control forms the largest single item of a maintenance operation. Traditional winter control measures include plowing, removal, salting (de-icing), and sanding. This article should have you consider your day-to-day activities in a different light, to help you move forward towards a more cost-effective and efficient winter maintenance operation.
Traditional snow and ice control (snow fighting) generally involves waiting until snow starts coming down and some accumulation has occurred, and then mobilizing equipment to remove snow from the road surface. Salt is then used to prevent liquid from freezing and forming a layer of ice known to be dangerous to drivers. The application of road salt to break the ice-pavement bond became known as "de-icing" operations. This approach has also been labelled as reactive. A proactive approach would be centred on preventing the ice-pavement bond from forming, rather than breaking it later properly with more material and effort. A proactive approach will allow for the adoption of the "System" approach for a well-integrated maintenance operation.
Let's step back and theorize a little about winter maintenance. We must look into our objective for the operation: A typical objective might be to "maintain adequate road access for safe passage of traffic in a timely and cost-effective manner." However, a more simplified operational objective for a winter maintenance provider would be "to use the right material, in the right amount, at the right time, in the right place." Such an objective will form the basis for a more cost-effective and efficient operation, not to mention a more environmentally-conscious one.
To further understand operational objectives, we need to look into elements that have the largest effect on the operation. Elements of winter maintenance may include policy, standards, materials, road and weather conditions, equipment, labour, technology, and methodology.
A road maintainer should establish a policy for his service delivery. A policy defines the minimum acceptable Level of Service (LOS). A policy would define the desired end condition; an example of a policy would be "bare pavement," "partial bare pavement," or even "snow packed" if it is in an area where snow-packed roads are best to have. A LOS is considered to be the maximum time to achieve the policy objective.
Now that the policy and LOS are in place, a mechanism is needed to facilitate delivery of the proper LOS to the various roads within a road network, keeping in mind that roads are not all equal and should be treated accordingly. Thus, the need arises for a roadway classification system, whereby the service level of each road is defined based on preset criteria. The selected criteria can be based on traffic volumes, speed limit, number of lanes, or any formulated combination thereof.
With the above accomplished, a plan has been started for winter maintenance operations. The plan should include consideration of the various elements mentioned above, and be used to establish predetermined operational routes (beats) for material application, snow plowing, snow removal, etc. The routes then should be optimized using intelligent computer software to achieve maximum utilization of available resources.
A plan would not be complete if it did not account for the type of equipment being used; speaking of which, we can see that the typical equipment that has been used over the years consists mainly of single-function units. A plow truck, with or without a wing plow, is used for snow plowing; older units required a second operator to operate the wing. At the same time, salting and sanding are performed using spreaders, with no plowing capabilities or very limited underbody plow. Winter maintenance professionals need to consider use of multipurpose equipment and combination units. Such equipment will help maximize available resources as well as maintain a reasonable work force.
While winter maintenance might be the largest expense for a road authority, the materials used in snow and ice control form the largest single ticket item of a winter maintenance budget. Therefore, when considering a chemical for de-icing operation, one should consider and understand the capabilities and limitation of such chemical; not only to establish what is the optimum working temperature for this chemical, but also to establish the proper working application rates and application methodology.
Building on the above, one should realize the fact that dry material (salt) does not melt snow and ice; the material has to be in a liquid solution before it has any effect. Thus, working with liquid de-icers may have merits. Liquids have a shorter response time for depressing the freezing point of water on the road due to snow and ice. Understanding the limitations of liquid de-icers opens the door for using pre-wetting and anti-icing techniques as winter maintenance tools. Use of liquids in pre-wetting and anti-icing will increase the retention of material or the road, shorten the time for the effect to take place, and help reduce the total amount of material used for the same level of effectiveness.
Another fact that has to be realized is that the temperature that affects the chemical and its application is pavement temperature, and not air temperature, since the contact is at the road surface. This makes pavement temperature a key factor in making decisions on the type and application of material used for snow and ice control. Pavement temperature can be monitored with mobile infrared temperature sensors, or as part of more elaborate systems such as Road Weather Information Systems (RWIS). RWIS allows network-wide monitoring of the near-live road conditions, as well as allows for the use of value-added services such as road temperature forecasting and road condition forecasting.
All of the technology will not give you the edge on winter unless it is accompanied by the proper training which is vital to the success of your plan. Training should encompass the various levels of the organization, from supervisory staff and spreader operators to the politicians, contractors, and the media.
Winter maintenance operations is a system with many complementing parts that must be taken in the light of each other's effect on the operation as a whole.
To reach Mohamed M. Alkoka, please call (613) 560-6094 ext. 21177, or send email to Mohamed.Alkoka@city.ottawa.on.ca.