Figure 1 Skagit River Bridge after collapse
Figure 2 Skagit River Bridge vertical clearance levels before collapse
In May 2013, a semitruck with an over-height load struck part of the Skagit River Bridge on Interstate 5, causing one span of the bridge to collapse into the water. The bridge’s highest vertical clearance of 18’ was located above the inside lanes; the vertical clearance above the outside lanes was only 15’ 6”. The truck had been inappropriately traveling in the outside lane. While the accident was not related to erroneous data or lack of signage, the National Transportation Safety Board recommended that the Washington State Department of Transportation create a way for the public to have better access to our vertical clearance data through GIS. In response, we've released a web map application called the Bridge Vertical Clearance Trip Planner. The application simplifies the process of planning the most effective and convenient routes through the state when moving over-height loads.
Previously, route planning was a complex process. Operators or permit applicants needed to locate each bridge or undercrossing entry in a WSDOT Bridge List document using milepost information, crossing name and location and then use their own paper maps to plan their routes, sub routes and detours. The Bridge Vertical Clearance Trip Planner makes the data more accessible in considerably less time, by presenting information from the Bridge Preservation database on a web-based map.
Figure 3 WSDOT Bridge List (pdf format)
With the new Bridge Vertical Clearance Trip Planner application, operators can quickly and accurately see which bridges and overpasses should be avoided or approached with caution. Drivers enter the height of their load, up to 16 feet, and enter a state route or interstate number, including state route ramps, spurs and couplets. The map legend populates with a total number of vertical restrictions, and the map display updates, showing where those restrictions are located, including bridges or overpasses that are not passable, in red, or ones that are passable but require a lane change for proper clearance, in yellow. Users can zoom in and click the point marker to obtain more detailed information about that restriction, including minimum and maximum vertical clearances, street level images, local agency contacts, permit information and other details about the structure.
Figure 4 Bridge app displaying results
Figure 5 pop up information displayed from clicking on a point
The project provided several opportunities for WSDOT to demonstrate its commitment to innovation. The bridge inventory database is organized to efficiently support lists of ‘crossing’ records, but not location geometry; much of the data needed to support the GIS had to be developed and added to the system. Additionally, the vertical clearance data contains multiple crossings, such as roadways on and or under a given structure, and more than one crossing for a given roadway location. In some cases it was necessary to split one record into multiple GIS events, and at other times multiple records were reduced to a single event. In some cases, multiple crossings exist in the same location, so a procedure was created to evaluate and merge duplicate locations onto a single point linked back to the original crossings. In the end, all 6200+ vertical clearance points were carefully checked to make sure each location was correct and that there were no duplicates or errors. The legacy database was also modified to hold the new data and an extract transform load process was developed to regularly update the new SQL database that supports the trip planner application. This process provides the most accurate and up-to-date information with a short turnaround.
As part of the overall effort to keep the information up to date and accurate, a new tool is being developed. The tool is intended to help the WSDOT bridge preservation team update bridge location geometry with an easy-to-use web interface that integrates with the current Bridge Works software. This tool may eventually be extended to cities and counties as well, so they can maintain the status of their bridge data. Keeping the information up to date and accurate is a top priority. This new tool should be in place by mid-2015. Working within funding constraints, WSDOT will continue to expand the trip planner functionality, with possible enhancements such as: displaying lane-by-lane height, directional information, city and county bridges.
We hope this tool and the steps taken within the department to make vertical clearance information easier to access will help the trucking community make safer travel decisions across our state.
As for the Skagit River Bridge, WSDOT crews completed all of the repair work by July 2014. They replaced the collapsed span, raised and reinforced the remaining bridge structure, giving it an equal 18-foot vertical clearance across all lanes, and retrofitted several bridge structural members with reinforced steel components to add strength should the bridge ever be struck again.
Figure 6 Skagit River Bridge after repair
Figure 7 Skagit River Bridge vertical clearances after repair