Fighting winter storms: a GIS approach to snow management.
GIS's core competency answers the question "where?" Using a map as a visual representation of the data modeled in the GIS, quick answers can be provided to questions like, "Where are my assets located?" "Where is there a shortfall in service?" "Where could my resources best be deployed under current conditions?"
Modeling data in a GIS allows for easy consideration of any number of "what if?" scenarios. By adjusting variables in the model representing constraints and available resources, different scenarios can be played out to reflect changing conditions.
Public agencies responsible for clearing streets and highways of ice and snow can get quick solutions concerning the amount of current or predicted snowfall, number of plows in operation, and cost of labor expended. This analytical capability makes GIS an excellent tool to support decisions based on large amounts of complex information. Plans of action can be created both in advance of storm events and as conditions change.
In the following scenario, GIS demonstrates its ability to determine the best course of action for the desired result within the given constraints. Constraints:
* Five inches of snowfall is predicted
* Two snowplows are out of service
* The temperature is right to spread salt.
* Reconfigure all snowplow routes to evenly distribute work load
* Maintain priority designation on main roads and emergency routes
* Estimate overtime expended
* Monitor amount of salt distributed by all vehicles.
GIS also can serve as a central hub to unify complementary technologies useful for fighting storms. Route optimization programs determine the most efficient paths and division of labor for a fleet of vehicles. Automatic vehicle location (AVL) displays the current location of vehicles on a map in real time. Weather forecast information can be displayed in a GIS, along with readings from local pavement temperature sensors. Information collected on miles driven by individual snowplows and the amount of deicers dispensed can be used to populate a GIS-centric asset management program, create vehicle maintenance schedules, and generate budgets and reports.
Although it is desirable to know where your snowplows are at any given moment while tackling a snow event, it is only half as useful if you don't know where they should be in the first place. Route optimization determines how to best commit available resources to a snow fight. In the first of two steps, the service area is partitioned into a number of routes equal to the number of available plows. This "turf cutting" also eliminates roads that do not fall within the agency's responsibility. The workload of each route is balanced against the others to make them roughly equal.
Secondly, each individual route is optimized to minimize deadhead time, such as transit to and from the maintenance yard or to the nearest salt dome. A primary goal is to minimize unproductive time with the plow blade in the up position. However, this must be conducted within the snow control policy established by the agency to meet a pre-established level of service for snow and ice control:
* First priority -- arterial streets and intersections connecting hospitals, fire stations, police stations, and emergency medical services
* Second priority -- minor arterials streets and those serving public facilities
* Third priority -- residential streets and all others.
Route generation also must consider the unique characteristics of the streets to be serviced. At the heart of the route optimization program is a street centerline network. This is a digital representation of each street segment in the service area along with rules about how that section of the street can be used by vehicles. Routes generated must obey the rules of the road, such as one-way streets or left-turn restrictions.
The output from a route optimization program results in a digital display of each numbered route shown on the map in a unique color. Standard data browser tools are easy to use: zoom in/out, pan, and full extent. The auto-tracing command demonstrates how a snowplow should progress though its route. A printout of turn-by-turn directions can be generated for the driver to use until the route is learned or for substitute drivers not familiar with the route.
Optimized routing also identifies the need to relocate staging facilities for deicing and aggregate materials. Salt domes often are not in the best location to service finely tuned routes. Repositioning existing facilities or adding new ones to further minimize downtime and fuel usage becomes an easier task.
AUTOMATIC VEHICLE LOCATION
AVL is the real-time depiction of in-service vehicles on a GIS map using a global positioning system (GPS) to establish location, and a communications link to relate this information to the GIS. The progress of snowplows equipped with AVL can be tracked remotely by supervisory personnel, and also by citizens if the information is made available via a city-maintained Web site. A "bread crumb" trail shows where roads already have been cleared.
In addition to current position, onboard sensors can relay other data back to the GIS. Of particular interest to supervisors are variables that affect the budget, such as deadhead time (plow up), operator break time, start/stop time of individual routes, amount of materials spread, fuel stops, and resumption of service.
Once captured, the information paints a complete picture of the resources expended in fighting a storm and removes much of the uncertainty involved in creating accurate budgets.
--Jeffrey Allen is a public works specialist at ESRI Inc., Redlands, Calif.
RELATED ARTICLE: Configuring an AVL system
Automatic vehicle location (AVL) technology uses a range of technologies--from satellites to computer workstations--to manage snowfighting vehicles. Source: ESRI Inc.
RELATED ARTICLE: A snowfighter's glossary
AVL (automatic vehicle location) -- The representation of a moving vehicle on a map using GPS to determine location and a communication link to transmit information.
Communications link -- In AVL applications, it is used to transmit information across distance. The most common format is a cellular phone link. A proprietary terrestrial (radio) network can be used, as well as a satellite-based link in rural settings where no other service is available. For simple "location only" applications, a GPS-enabled Nextel phone is an inexpensive option.
GPS (global positioning system) -- A constellation of 24 satellites, developed by the U.S. Department of Defense, that orbits the earth at an altitude of 20,200 km. These satellites transmit signals that allow a GPS receiver anywhere on earth to calculate its own location.
Load balancing -- An equitable division of labor among all snow-plow operators covering a service area.
Logical network -- An assemblage of behavioral rules associated with a particular road feature, such as speed limit, one- or two-way traffic, or turn restrictions of an intersection.
Network -- An interconnected set of lines and points representing geographic features, such as roads and intersections, on which resources can be moved; a digital representation of streets and their features.
Street data -- A network data set representing a service area of particular interest. Many agencies maintain their own data, purchase commercially available data, or use a combination of both.
Turf cutting -- As it pertains to snow fighting, the partitioning of a service area into discrete subsets, each served by one snowplow.