Tuesday, October 18, 2011
Sunday, October 16, 2011
Sunday, October 9, 2011
"A functionally obsolete bridge is one that was built to standards that are not used today. These bridges are not automatically rated as structurally deficient, nor are they inherently unsafe. Functionally obsolete bridges are those that do not have adequate lane widths, shoulder widths, or vertical clearances to serve current traffic demand, or those that may be occasionally flooded.
A functionally obsolete bridge is similar to an older house. A house built in 1950 might be perfectly acceptable to live in, but it does not meet all of today’s building codes. Yet, when it comes time to consider upgrading that house or making improvements, the owner must look at ways to bring the structure up to current standards.
A bridge sufficiency rating includes a multitude of factors: inspection results of the structural condition of the bridge, traffic volumes, number of lanes, road widths, clearances, and importance for national security and public use, to name just a few.
The sufficiency rating is calculated per a formula defined in Federal Highway Administration’s Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges. This rating is indicative of a bridge’s sufficiency to remain in service. The formula places 55 percent value on the structural condition of the bridge, 30 percent on its serviceability and obsolescence, and 15 percent on its essentiality to public use.
The point calculation is based on a 0-100 scale and it compares the existing bridge to a new bridge designed to current engineering standards.
The bridge’s sufficiency rating provides an overall measure of the bridge’s condition and is used to determine eligibility for federal funds. Bridges are considered structurally deficient if significant load carrying elements are found to be in poor condition due to deterioration or the adequacy of the waterway opening provided by the bridge is determined to be extremely insufficient to point of causing intolerable traffic interruptions.
Every bridge constructed goes through a natural deterioration or aging process, although each bridge is unique in the way it ages.
The fact that a bridge is classified under the federal definition as “structurally deficient" does not imply that it is unsafe. A structurally deficient bridge, when left open to traffic, typically requires significant maintenance and repair to remain in service and eventual rehabilitation or replacement to address deficiencies. To remain in service, structurally deficient bridges are often posted with weight limits to restrict the gross weight of vehicles using the bridges to less than the maximum weight typically allowed by statute.
To be eligible for federal aid the following is necessary (a local match is required):
- Replacement: bridge must have a sufficiency rating of less than 50 and be either functionally obsolete or structurally deficient.
- Repair: bridge must have a sufficiency rating of less than 80 and the jurisdiction is prevented from using any additional federal aid for 10 years.
- The $3 billion East Side Access tunnel will bring Long Island Railroad commuter trains into Grand Central Station by 2016
- Construction of the 8.5-mile, $17 billion Second Avenue Subway resumed in 2007 after a 30-year hiatus. The first 3-station segment is scheduled to open in 2016.
- Construction of an extension of the #7 subway from Times Square southwest to Chelsea is underway and will be completed in 2013. This project sets the stage for further extension of the line beneath the Hudson River to New Jersey.