Research Project Statement s3

Research Project Statement Fiscal Year 2003

Project Number: 0-4510 Modification? Yes No

Title: Evaluate Equipment, Methods, and Pavement Design Implications for Texas Conditions of the AASHTO 2002 Axle-load Spectra Traffic Methodology

RMC Number: 1 Strategic Issue 4: Traffic Characterization

Developed By: Joe Leidy, P.E.; Dr. German Claros, P.E.

Project Statement Date: January 4, 2002 TxDOT Project Name Office Area Email Fax Number Personnel Code/Phone Number Program Coordinator (PC) Dr. German Claros, P.E. RTI 512 467 3881 [email protected] 512 465 7486 Project Director (PD) Joe Leidy, P.E. CST-M&P 512 506 5848 [email protected] 512 506 5839

Project Monitoring TBD Committee (PMC) (Project Advisors Optional) Duration (# of years): 2 Total Budget: $ Budget by year: First Year FY $ Other Funding Available? Yes No Second Year FY $ Additional FYs $ Project Description: A monumental effort is underway to change the way cumulative traffic loads are accounted for in the pavement design process. Current state of the practice for most State Highway Authorities (SHA) is to estimate cumulative traffic in terms of 18-kip ESALs. In AASHTO’s 2002 mechanistic design process, traffic will be accounted for in terms of a highway’s “axle load spectra,” a cumulative reconciling of axle loads grouped into discrete “bins” by axle group configuration (single, tandem, tridem, quad). For the most critical design cases (level 1), WIM data from the highway to be rehabilitated or reconstructed is to be used with appropriate growth factors, projected to the length of the analysis period. Highways to be constructed on new right of way would require traffic estimated loading data from highways in close proximity, particularly those used as connecting routes. For less critical design cases, appropriate “regional” axle load spectra data for facilities with similar truck volume and site-specific classification breakout will be used (level 2). Finally, for the least critical designs, actual traffic counts will be used in conjunction with regional classification and WIM breakouts (level 3).

Currently, there are only 15 continuous WIM stations in Texas, with the majority of these on interstate facilities. What WIM coverage “density” and sampling frequency is necessary to insure adequate traffic forecasting is still open to debate. However, the recently completed study 0-1801 lists acquisition of additional weigh sites in compliance with the Traffic Monitoring Guide and better diversification of new sites as “essential enhancements.” Currently TxDOT does not have adequate regional representation of weigh data and uses a “state-wide average” to generate load data for most highways. The 0-1801 study indicates that a variation of up to 40% in ESAL forecasts could be derived from relying on non-project specific weigh site data to represent traffic loading at the project location. This magnitude of error in forecasting loading can also be realized using the axle load spectra. Also included in the 0-1801 study are recommendations for improved evaluation of calibration standards. What minimal level of acceptable precision by WIM devices has not been specifically addressed (e.g., not all WIM equipment can deliver axle loads within 10% of the static axle load). Setting a fixed level of WIM precision is complicated by the uncertainties of forecasting traffic for 20 to 40 years in the future. Similarly, the density of vehicle classification and count devices to support designs using regional WIM data may need to be defined.

Research to be Performed: 1. The researcher must identify issues in the collection, data reduction and end use aspects of axle load spectra data. Data collection issues include: Procedures to determine the density and sampling frequency of WIM

of 2 systems needed to provide adequate coverage for high-type traffic facilities and regional requirements must be identified/developed. Required d 2. Densities of continuous classification and count devices to support level 2 and 3 designs are needed. 3. Recommendations as to the required accuracy and calibration regimen of WIM devices considering the potential inaccuracies of traffic forecasting must be investigated. Data reduction issues include investigating possible changes in the way TP&P currently reduces WIM data to allow for integration with the AASHTO traffic module. The amount of storage required to support 10 years of axle-load history by weigh location as recommended by 0-1801 should be further investigated. 4. The time requirements to conduct a project specific traffic analysis (by design level) and the procedure/format for transferring the traffic analysis to the designer should be identified. End use issues include: establishing guidelines on which level of design is appropriate, establishing state/district default parameters, and calibrating/ validating design thickness results. It is recognized that the full calibration/validation process will include updated material properties and distress considerations in addition to the new methodology for classifying traffic loading. The responsibility for establishing which growth function and traffic distribution options to use should be explored. 5. Develop “regional” axle load spectra with available data for application on level 2 analysis and level 3 analysis using traffic counts, regional traffic classifications and WIM breakouts.

Minimum deliverables are: Deliverable Products  A report should be rendered within 6 months that addresses topics related to data collection issues (see And Reports: Research to be Performed). A thorough review of Report 1801-1 is required. Conclusions from other sources should also be included.  A report addressing topics related to data reduction (see Research to be Performed) should be delivered at the end of the first year.  A Final Report that fully documents the research performed, findings and recommendations and that addresses end use issues (see Research to be Performed) is required by the end of the second year.  A separate guide addressing selection of design level and recommended traffic-related default values is required.  A Project Summary Report concisely outlining the research, findings and recommendations for implementation (4 pages).

Implementation: If recommendations require extensive additions to the Department’s automated data collection system (counters, classifiers, WIM), a multi-year implementation plan should be drafted. Recommendations made regarding changes to the way the Transportation Planning and Programming Division currently collects and stores traffic data should be worked out prior to the Department accepting AASHTO 2002 design procedures as the preferred method. Guidelines for the selection of design level and recommended traffic- related default values should be disseminated to the appropriate level within the Department following review by the project advisory committee.

Pre-Proposal Meeting: Yes No Thursday, March 7, 2002, 9:30 a.m., RTI, Camp Hubbard, 4000 Jackson Street, Bldg. 1, Alamo Room, 2nd floor

Sole-Source Project: Yes No

Project Rating & Justification: Mandated Critical Important Desirable 1. Schedule of Activities should include a column next to the Task/Description column that Additional Information: shows estimated percentages of the total project budget for each task. This information will be used to help the PC/PD more completely understand the level of effort that is planned for each task. 2. The Project Director will require monthly updates from the researcher, and as a minimum will schedule project meetings around October and April. Project kickoff and wrap-up meetings may be scheduled. 1. All individuals interested in proposing are encouraged to contact the PC and PD by February Deadlines (for RTI use only): 15, 2002. 2. All proposals from researchers should be sent directly to your university Research Liaison’s office for final submission to RTI. The Research Liaison is TxDOT’s official point of contact with the university. 3. Proposals are due to RTI by 4 p.m. on March 27, 2002.

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