What is being displayed?
During a winter storm, SDOT sends out a fleet of vehicles equipped with GPS tracking systems. Some vehicles have a plow blade; others have de-icing or spreader equipment. The map shows the recent path of these vehicles that have been dispatched to respond to the winter weather event split into different time frames.
What does Service Goals mean?
The purpose of SDOT's Storm Response is to maintain mobility on Seattle's streets and access to the regional transportation system. SDOT has a goal of achieving pavement clear of snow and ice on specified streets within twelve hours after a lull in the storm. The map displays our planned response routes based upon:
What are Reported Obstacles?
Streets are closed by the Seattle Police Department (SPD) when they are deemed either unsafe for vehicular travel and/or may have obstacles in the roadway. SPD will place signs on the street to prevent vehicles from using the roadway. These reported obstacles are indicated as a red hexagon at the mid-point of the applicable segment. If a street is treated by SDOT's Street Maintenance Division and/or becomes passable again, then the closure signs are removed and the red hexagon is removed from the map.
Why are some of the vehicles displayed not following the streets?
The GPS (Global Positioning System) coordinates are obtained from satellite signals several times per minute as the vehicles are traveling on the streets. The system needs a strong signal from at least four different satellites to get a reasonably accurate reading. Although the accuracy will never be better than plus or minus 5 meters, when the signals are partially blocked by tall buildings or heavy tree cover, the accuracy will be much less, possibly several hundred meters from the actual location. The vehicle paths in downtown Seattle show this effect, with travel routes crossing through buildings and following what appears to be an erratic course. Very rarely, a coordinate will be so far off that the path line may suddenly deviate by a mile or more before returning to the original route.
Why don't I see any vehicle paths on the map?
Vehicle paths are only shown on the map after an SDOT operations staff enables the display for a specific vehicle. This will normally happen at the time a vehicle is dispatched to perform winter weather response activities. However, the systems that support the map must be powered off for maintenance purposes every night between 1:00am and 1:30am. The map will not display any information during this maintenance time.
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