An Evaluation of the Condition of the Nation s Bridge Infrastructure Using Indicators Extracted from National Bridge Inventory Source Files

Transcription

1 McClure, Daniell and Langehennig 1 An Evaluation of the Condition of the Nation s Bridge Infrastructure Using Indicators Extracted from National Bridge Inventory Source Files Authors: Scott McClure, P.E. Research Bureau Chief New Mexico Department of Transportation 7500 Pan American Freeway NE PO Box Albuquerque, NM Telephone: Fax: Scott.McClure@state.nm.us Keli Daniell. M.A., Corresponding Author Management Analyst New Mexico Department of Transportation 7500 Pan American Freeway NE PO Box Albuquerque, NM Telephone: Fax: Keli.Daniell@state.nm.us Michelle Langehennig I.T. Applications Developer New Mexico Department of Transportation 7500 Pan American Freeway NE PO Box Albuquerque, NM Telephone: Fax: Michelle.Langehennig@state.nm.us Submission Date: November 7, 2012 Keywords: National Bridge Inventory, NBI, software, bridges, evaluation NBI, deficient bridges Word Count: 3127 Number of Figures: 13

2 McClure, Daniell and Langehennig 2 ABSTRACT As bridges continue to age and deteriorate, the Nation is facing enormous repair, maintenance and replacement costs, as well as an increase in safety hazards to the motoring public and a decrease in efficiency to the trucking industry. Bridge conditions are of immediate concern to public safety, economy and national security. Compounding the issue is a chronic lack of adequate resources to perform recommended maintenance and repair, a continual increase in the weight and numbers of heavy commercial vehicles, and a reduction in the number of new bridges built or replaced annually in recent years. Essential to addressing this issue is a simple to use, easily accessible means to assess current conditions and to identify specific historical trends that may contribute to these conditions. For the past two decades the primary source of publicly available information on the condition of the nation s bridge infrastructure has been the National Bridge Inventory (NBI) data files compiled and provided by the Federal Highway Administration. This paper presents the results of efforts by the Research Bureau of the New Mexico Department of Transportation to produce a user-friendly bridge information system that uses readily available NBI source files, and to examine ten specific indicators of the condition of the nation s bridge inventory using data extracted from these files. These indicators are described in Federal Report No. MH , National Bridge Inspection Program: Assessment of FHWA s Implementation of Data-Driven, Risk-Based Oversight, and pertain primarily to the load rating and posting status of the nation s bridges.

3 McClure, Daniell and Langehennig 3 OVERVIEW In 2010 the Research Bureau of the New Mexico Department of Transportation (NMDOT) produced a prototype of a software application, the SABIS Bridge Information System (SABIS, an acronym for Special Application Bridge Information System), that processes National Bridge Inventory source files available through the Federal Highway Administration (FHWA) website [1], populates State-specific databases, and provides a simplified means for reviewing detailed information on each of the approximately 600,000 public bridges in the inventory and for generating reports of commonly requested information. This effort is described in an earlier technical paper, Development of User-Friendly Software for Extracting Information from National Bridge Inventory Source Files, as published in the Transportation Research Record in December 2010 [2]. Improvement and refinement of this application is ongoing, and in 2012 the authors completely redesigned and recoded the software in the Microsoft.NET programming environment as a means to ensure continuity of service with newer 64 bit operating systems. The application is considered to be in an evaluation phase at the time of this report. The information available through the NBI database presents an opportunity to study bridge conditions and trends over the twenty years of available data. For example, Figure 1 presents a chart showing the age of structures based on the 2011 NBI database as determined from NBI Item No. 27, Year Built. The mean and median age of structures less than 100 years old in this population is 40 years, and the chart indicates the trend of new bridge construction over the last century. Evident from this chart is a general reduction in the number of new bridges built or replaced annually in recent years. According to the latest information available at the time of this report, new bridge construction is at its lowest point in nearly sixty years. The NBI database indicates that approximately 6300 new bridges were added to the inventory in program year 2010, and that over 100,000 bridges currently in the inventory are recommended for replacement due to substandard load carrying capacity or substandard roadway geometry. Figure 2 presents the recommended improvement costs as derived by SABIS from the NBI database for program years 1992 through Three cost categories are shown: a) roadway improvement cost; b) bridge improvement cost; and c) total improvement cost, which is typically higher than the sum of a) and b). The chart indicates a general annual upward trend in the cost of bridge improvements, and the annual increase in cost appears to be dramatically higher than the approximately $4 - $6 Billion allocated annually by the Federal government for bridge replacement and rehabilitation. The dark line toward the bottom of this chart shows the Federal Highway Bridge Program (FHBP) funding for the period of 1998 through From historical data extracted from the NBI database, it s apparent that recommended bridge improvement costs have more than doubled, from $99.5 Billion to $209.4 Billion over the twenty year period from 1992 through According to the Apportionment of Bridge Replacement and Rehabilitation tables available through the FHWA website [3], the annual amount apportioned for the Federal Highway Bridge Program increased by $1.5 Billion over a ten year period, from $4.4 Billion in 2002 to $5.9 Billion in According to the NBI database, the reported cost of recommended bridge improvements rose by $85.8 Billion, from $123.6 Billion to $209.4 Billion during that period. The amount of the Federal Highway Bridge Program constitutes 3.6% of the reported recommended bridge improvement cost in 2002, and 2.8% in While the funding programmed for the Federal Bridge Program is available for the program years indicated, it s noteworthy that with the MAP-21 transportation bill, funding for bridge projects is variable and may not be as readily apparent in future years. BACKGROUND A natural extension of the SABIS project is to use the information encoded in State NBI databases to gain insight into the health and condition of the nation s bridge infrastructure. In 2011 the Research Bureau of NMDOT created a series of subroutines that use these State-specific databases to generate national maps and reports on bridges in ten general categories, primarily related to load rating and bridge posting. The objective of this effort is two-fold. The first is to demonstrate the utility of the SABIS Bridge Information System as an effective tool for the general examination of bridge conditions and trends as encoded in NBI

4 McClure, Daniell and Langehennig 4 source files, and the second is to present the results of a targeted study of the nation s bridge infrastructure using indicators established by the Federal Highway Administration (FHWA). These reports are based on descriptions of condition indicators presented in an attachment to Federal Report MH , National Bridge Inspection Program: Assessment of FHWA s Implementation of Data- Driven, Risk-Based Oversight [4]. These ten reports are intended to assist FHWA Division Offices in evaluating States compliance with National Bridge Inspection Standards (NBIS) as documented in Federal regulation 23CFR650 Subpart C, National Bridge Inspection Standards (NBIS) [5]. Following is a list of indicators described in Federal Report MH Report 1. Identifies bridges with an operating rating of less than 36 U.S. tons; but they have not been posted. The report identifies bridges that may be open to vehicles that are too heavy to cross. Report 2. Identifies bridges with an operating rating of less than the maximum legal load; but they have not been posted. The report identifies bridges that may be open to vehicles that are too heavy to cross. Report 3. Identifies bridges for which no operating rating analysis was performed. The report identifies bridges that may not be properly rated for their safe-load carrying capacity. Report 4. Identifies bridges that have been recommended for posting; but they do not have legally implemented signs. The report identifies bridges that should be posted, but are not. Report 5. Identifies bridges with a superstructure condition rating less than or equal to 4 (poor condition) and have not been posted. This report identifies bridges that may not have their deteriorated condition properly accounted for in their load rating. Report 6. Identifies bridges with an operating rating of less than 3 U.S. tons; but open for service. The report identifies bridges that must be closed, but are not. Report 7. Identifies bridges with a change in wearing surface, but no change in their operating rating. The report identifies bridges that may not have changes in the weight of the bridge properly accounted for in their load rating. Report 8. Identifies bridges that have been reconstructed and report no change in their operating rating. The report identifies bridges that may not have the structural improvements following a reconstruction properly accounted for in their load rating. Report 9. Identifies bridges with a change in superstructure, substructure, or culvert condition rating to 4 (poor condition) or less from a higher value with no change in their operating rating. Also identifies bridges with a change to 2 or less from a higher structural evaluation appraisal rating with no change in their operating rating. The report identifies bridges that may not have their deteriorated condition properly accounted for in their load rating. Report 10. Identifies bridges that have been structurally deficient for 10 consecutive years. The report identifies bridges that should likely be programmed for replacement or rehabilitation. These report descriptions are taken verbatim from Federal Report No. MH [4], and using these descriptions the authors created a batch processing application that queries the NBI database for bridges that meet these criteria. In preparing these reports the authors made various basic assumptions including, for example, that bridges designated as structurally deficient in one program year and also ten years later (Report 10) remained in that designation during all of the intervening years. Similarly, for Report 7, the authors chose a ten year comparison period with the assumption that there are no

5 McClure, Daniell and Langehennig 5 intermediate changes to the wearing surface between the first and last program years. The state NBI databases were queried for selection criteria as described above in accordance with guidance provided in Publication FHWA-PD , Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation s Bridges (NBI Coding Guide) [6]. Report 6, for example, lists bridges with an operating load rating of less than 3 tons and open for service. The NBI Coding Guide specifies that bridges that are unable to support a minimum of 2.7 metric tons (3 standard tons) should be coded as 000 and closed to traffic. SABIS uses this convention when evaluating the criteria and filters the database for bridges with an operating load rating of 000 and a posting status not equal to K (not closed to traffic). In one state with an unusually large number of bridges in this category, all have operating load ratings coded as 000 and a posting status coded as E, which indicates that a temporary structure is in place to carry legal loads while the original structure is closed, and all are owned by local agencies. No attempt is made by the authors to interpret these results, to determine differences in the way that owner agencies report data, or to speculate as to causative factors, as this is better left to owner agencies. The subroutines created to prepare these reports produce formatted files that list all bridges meeting the selection criteria, and a coordinate file that may be used to plot structures using a third party mapping application. Reports are generated for each State and summarized for the nation as a whole. In all, over 1000 individual reports were generated through batch processing operations for program year These reports present an opportunity to perform comparisons among States, and to investigate historical trends in a particular State or region using the 20 years of historical data provided by the FHWA and processed through the SABIS software. RESULTS Table 1 presents a State by State summary of the numbers of bridges that fall into these categories. The queries used in generating these reports are based on available NBI data and include on-system and offsystem bridges, as well as structures owned or maintained by various local, State and Federal agencies, It should be noted that there is likely variation between States in the way that some data are reported, which may give rise to some of the differences in the reported number of bridges in these categories. The results of the query are presented as-is without an attempt by the authors to interpret these results. With further modification these reports could be refined to filter and sort by classification, age, owner, material and design type, location or other combinations of criteria with minimal effort. Figures 3 through 7 show the distribution of bridges in these categories as plotted on a map of the contiguous United States. While the reports produced by SABIS provide only identifying information for bridges in each report category in tabular format, the application is highly interactive and the user may easily obtain detailed information on a particular structure. If the user clicks on a bridge number in a report, SABIS jumps to a detailed report for that structure and plots its location on a state map. From this page the user may use a hyperlink utility to view the selected bridge in Google Maps. Figures 8 and 9 illustrate these functions for a bridge in California identified from Report 10, Structurally Deficient for Ten Years. SUMMARY In 2010 the New Mexico Department of Transportation (NMDOT) completed work on a preliminary prototype of the SABIS Bridge Information System (SABIS). Testing, evaluation and refinement of the application are ongoing and in 2012 the authors completely redesigned and recoded the application using the latest available software development tools. SABIS processes publicly available data encoded in National Bridge Inventory (NBI) source files as collected and compiled annually by the Federal Highway Administration (FHWA). Unlike the Pontis bridge management program, an AASHTOWare Bridge product which serves the bridge management needs of owner agencies, SABIS is a more modest application created for use by technical and non-technical users who require a simple means for reviewing the wealth of information available in the NBI Database. SABIS provides simplified access to NBI data compiled by the FHWA since The application serves as a general bridge information system, with the means to access commonly requested reports, multimedia resources including digital images and video, bridge inspection reports if available, and internet content. The program uses approximately 1000

6 McClure, Daniell and Langehennig 6 State-specific NBI databases to produce 25,000 standard reports and to access 10 million individual bridge records using twenty years of available data. A memo from the U.S. Department of Transportation (USDOT) designated as Federal Report No. MH [4] includes an attachment that describes ten reports being developed to assist the FHWA Division Bridge Engineers in evaluating States compliance with the National Bridge Inspection Standards (NBIS) [5]. These reports are primarily related to load rating and posting status, and use criteria from the National Bridge Inventory database. As a means to evaluate the utility of SABIS as a viable research tool, the authors created a supplemental application to duplicate these reports. The application permits users to generate reports for an individual State, or to perform batch processing for all States in the inventory for a given program year. The application creates a report which includes a plot of bridges meeting appropriate criteria on a State map. The program is interactive and permits users to click on a bridge in a report and jump to a summary file of the selected structure and to plot the structure to a map. Separate report and coordinate files are created in the event that a user needs to customize reports using a third party mapping application. The program includes a link to Federal Report No. FHWA-PD , Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation s Bridges (Coding Guide) [6] as a reference for users. Figure 10 presents a representative screenshot of one the reports, Report No. 3 Bridges with no Load Rating Performed, as described in Federal Report No. MH [4]. The program permits users to compare conditions between various States and regions. Figure 11 presents a visual comparison of structurally deficient bridges in three midwestern States. Figure 11.(a) displays the distribution of bridges classified as structurally deficient in the 2011 NBI database. Figure 11.(b) displays bridges which have been in this condition for 10 or more years. Nationally, approximately 44% of the 67,500 bridges designated as structurally deficient in the 2011 NBI database have been in that condition for ten or more years, and approximately 20% have been structurally deficient for twenty or more years. In addition to comparing bridge conditions between States, the NBI database may be used to evaluate historical trends. Figure 12 displays a chart of the number of bridges in the inventory designated as structurally deficient for NBI program years This chart demonstrates a continual reduction in the number of structures in this classification during this period. CONCLUSION The objectives of this report are two-fold. The first is to demonstrate the utility of the SABIS Bridge Information System as a viable research tool, and the second is to present the results of a targeted study of bridge condition indicators in the United States through the use of this tool using ten specific indicators as identified by the Federal government. Results of the analysis herein are provided as-is on the assumption that NBI source data is reasonably accurate, and speculation as to the potential causes for these results is beyond the scope of this report. While the authors have made every effort to ensure the accuracy of the subroutines created in preparing the reports used in this analysis, the SABIS Bridge Information System continues to be in a state of development, and the research community is invited to independently confirm or refute these findings. The results from the study of bridges in the ten categories summarized in this report identify a large number of structures for which the load rating is suspect or for which the posting status is inadequate. Load rating and posting status are of immediate safety concern, and studies of this nature present an opportunity to target specific structures for corrective action. Likewise, a bridge information system such as SABIS may provide the means for researchers and others to perform detailed analysis of NBI data to serve particular needs. ACKNOWLEDGEMENTS The authors gratefully acknowledge the technical support and assistance provided by Dr. Thiet Nguyen, who serves as Bridge Engineer for the New Mexico Division of the Federal Highway Administration. For

7 McClure, Daniell and Langehennig 7 more information on the SABIS Bridge Information System, contact the project manager at Keli.Daniell@state.nm.us.

8 McClure, Daniell and Langehennig 8 REFERENCES 1. NBI ASCII Files. FHWA, U.S, Department of Transportation McClure, S., and K. Daniell. Development of a User-Friendly Software Application for Extracting Information from National Bridge Inventory Source Files. Transportation Research Record, No.2202, Transportation Research Board of the National Academies, Washington, D.C Apportionment of Bridge Replacement and Rehabilitation tables. FHWA, U.S, Department of Transportation National Bridge Inspection Program: Assessment of FHWA s Implementation of Data-Driven, Risk- Based Oversight. Memo referenced as MH U.S. Department of Transportation National Bridge Inspection Standards. 23CFR650C. FHWA, U.S. Department of Transportation Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation s Bridge. Publication FHWA-PD FHWA, U.S. Department of Transportation

9 McClure, Daniell and Langehennig 9 LIST OF TABLES AND FIGURES Tables TABLE 1 Summary of Number of Bridges by State and Category Figures FIGURE 1 Age Distribution of Bridges FIGURE 2 Bridge Improvement Costs FIGURE 3 Distribution of Bridges in Report Categories 1and 2 FIGURE 4 Distribution of Bridges in Report Categories 3 and 4 FIGURE 5 Distribution of Bridges in Report Categories 5 and 6 FIGURE 6 Distribution of Bridges in Report Categories 7 and 8 FIGURE 7 Distribution of Bridges in Report Categories 9 and 10 FIGURE 8 Screenshot of the SABIS Bridge Information System displaying a detail report of a structurally deficient bridge FIGURE 9 Google Maps display of Bridge No R in California as identified through Report 10 FIGURE 11 a and b Bridges in Midwest Classified as Structurally Deficient FIGURE 12 Structurally deficient bridges by NBI program year

10 McClure, Daniell and Langehennig 10 TABLE 1 Summary of Number of Bridges by State and Category; Source: 2011 NBI Database

11 McClure, Daniell and Langehennig 11 FIGURE 1 Age Distribution of Bridges; Source: 2011 National Bridge Inventory Database.

12 McClure, Daniell and Langehennig 12 FIGURE 2 Bridge Improvement Costs ; and Highway Bridge Program expenditures, Source: National Bridge Inventory Database and Apportionment of Bridge Replacement and Rehabilitation tables, Federal Highway Administration.

13 McClure, Daniell and Langehennig 13 FIGURE 3 Distribution of Bridges in Report Categories 1, (Operating Rating > 36 Tons, Not Posted); and 2 (Operating Rating < Max Legal Load, Not Posted) Source: 2011 NBI Database.

14 McClure, Daniell and Langehennig 14 FIGURE 4 Distribution of Bridges in Report Categories 3 (No Op. Rating Analysis Performed) and 4 (Recommended for Posting, but Posting not Legally Implemented); Source: 2011 NBI Database.

15 McClure, Daniell and Langehennig 15 FIGURE 5 Distribution of Bridges in Report Categories 5 (Poor or Worse Superstructure Condition Rating, Not Posted) and 6 (Operating Rating < 3 Tons, Open for Service); Source: 2011 NBI Database.

16 McClure, Daniell and Langehennig 16 FIGURE 6 Distribution of Bridges in Report Categories 7 (Change in Wearing Surface, No Change in Operating Rating) and 8 (Reconstructed, No Change in Operating Rating); Source: 2011 NBI Database.

17 McClure, Daniell and Langehennig 17 FIGURE 7 Distribution of Bridges in Report Categories 9 (Change in Condition Rating to Poor or Worse from a Higher Rating, No Change in Operating Rating) and 10 Structurally Deficient for Ten Consecutive Years); Source: 2011 NBI Database.

18 McClure, Daniell and Langehennig 18 FIGURE 8 Screenshot of the SABIS Bridge Information System displaying a detail report of a structurally deficient bridge. Source: 2011 NBI database.

19 McClure, Daniell and Langehennig 19 FIGURE 9 Google Maps display of Bridge No R in California as identified through Report 10, Structurally Deficient for Ten Years.

20 McClure, Daniell and Langehennig 20 FIGURE 10 Screenshot of SABIS displaying bridges in New Mexico for which no operating rating analysis was performed. Source: 2011 NBI Database.

21 McClure, Daniell and Langehennig 21 FIGURE 11 (a) FIGURE 11 (b) (a) (b) Distribution of bridges in three Midwestern States (Colorado, Kansas, Nebraska) currently classified as structurally deficient. Distribution of bridges which have remained in the structurally deficient category for ten or more years. Source: NBI Database.

22 McClure, Daniell and Langehennig 22 FIGURE 12 Structurally deficient bridges by NBI program year. Source: NBI Database; Program Years