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50 CHAPTER SEVEN CONCLUSIONS INTRODUCTION The objective of this synthesis is to document the state of the practice of alternate design/alternate bid (ADAB) for pavement projects in state transportation agencies as a means of pavement-type selection. Each synthesis chapter concluded with a summary section that articulated the conclusions, effective practices, and suggestions for future research. This chapter con- solidates and synthesizes those summaries into a single area and offers observations on the state of the practice as delineated by the literature, survey results, and case studies. CONCLUSIONS The synthesis found that ADAB has received considerable acceptance by state transportation agencies as a result of its reported benefits in increasing competition and reducing pavement material costs. Missouri Department of Transportation reported an average increase of two more bidders per letting, and a 5% to 8% decrease in price in asphalt and concrete pav- ing prices in over 187 lettings. Other states recorded similar findings. Those DOT survey respondents that did not use ADAB were interested in future implementation to avail themselves of those demonstrated benefits. An ADAB was found to be the pavement-type selection based on real-time pricing for both alternatives. The second major conclusion is that the agenciesâ adoption of life-cycle cost (LCC)-based adjustment factors is far from unanimous, despite the well-grounded theoretical need for its use. Missouri DOT has performed the most ADAB projects to date, and has reported that the LCC-based bid adjustment only made a difference in four of 187 lettings. The policy to not use an adjustment factor for projects below its minimum size has been successfully used since 2003. Six of the 16 DOTs that use ADAB reported that they did not use an adjustment factor. In summary, ADAB procurement has successfully applied both with and without an LCC-based bid adjustment factor. Other conclusions reached in the synthesis are provided here: 1. Based on survey results, engineers are using the AASHTO-MEPDG (MechanisticâEmpirical Pavement Design Guide) methodology as a common platform when developing equivalent pavement designs for ADAB alternatives. 2. The wide-ranging assumptions behind life-cycle cost analysis (LCCA) calculations may lead to equally plausible LCC- based bid adjustment factors, which could be pivotal in determining the winning alternatives. There is no universally accepted solution for developing an LCC-based bid adjustment factor. 3. Because ADAB furnishes a means to compete current market pricing, which eliminates the need to make unreliable cost assumptions, ADAB can be expected to provide a straightforward solution to making pavement-type selections during volatile periods in pavement material prices. 4. For DOTs that do not currently practice an LCC-based pavement-type selection, ADAB offers a comprehensive evalu- ation process. 5. The synthesis found that significant variations exist among agencies in their development and use of ADAB methods. 6. Agencies that perceive higher benefits from ADAB also were found to have formal processes in both alternate bidding and pavement-type selection, as well as a longer history of alternate bidding and higher numbers of bidders per letting. 7. Implementing ADAB increases competition by allowing both HMA and PCC paving contractors to bid on the same job. Increased competition has been reported to result in more favorable pricing.
51 8. ADAB has been successfully employed under DBB, DB, and DBF project delivery methods. The case study projects presented cited benefits from ADAB practices. EFFECTIVE PRACTICES A number of effective practices were also identified in the preparation of the synthesis. Effective practices were identified if their successful use was reported in the literature, agency reports, survey responses, and case studies. One practice found to be effective was the use of deliberate industry outreach programs to ensure the ADAB program is both well understood and accepted. Giving the industry a voice in the development of ADAB procedures adds value to the programâs overall acceptance. Other effective practices are as follows: 1. Use of the MEPDG methodology to generate the equivalent design alternatives; 2. Using ADAB without an LCC-based adjustment factor could still benefit agencies in their pavement-type selection decisions. The agencies could benefit from the relative simplicity in this approach, despite losing the theoretical preci- sion that an LCCA-based adjustment factor is thought to contribute; 3. Establishing threshold criteria based on the LCC differential of competing alternatives or projectsâ surface area was also reported to further simplify the screening processes to determine which projects are candidates for ADAB procurement; 4. The stochastic LCCA approach removes the need to make deterministic assumptions for input values by allowing each to vary over its historic range in values. The resulting LCC for each pavement-type alternative allows the agency to make decisions using the associated confidence intervals calculated by the stochastic models; 5. If the construction schedule associated with each alternative pavement type is a concern, a time value component, such as A+B and lane rental methods, can be added to the ADAB equation to determine the winning bidder; 6. Simplifying the LCC factor input values reduces the amount of input data that must be collected to conduct LCCA; and 7. Maximizing both the clarity and transparency of the ADAB process by publishing the value of the LCC-based bid adjustment factor was also reported to facilitate industry acceptance. SUGGESTIONS FOR FUTURE RESEARCH The study found that a number of SEP-14 project reports recommend future research to develop better specifications for equivalent designs for ADAB projects. Both the survey and one SEP-14 project report specifically pointed to a need for addi- tional guidance on mixture tolerances. The study by De Jarnette et al. (2013) underlined the need to investigate the use of pay factors based on performance testing as a means for agencies to establish relationships between material properties, perfor- mance, and cost. Last, the survey results indicated that the use of the MEPDG to generate pavement-type alternatives was an effective practice, but there is no research that quantifies the benefits of that approach over pre-MEPDG pavement design methods. These topics could be integrated into a single NCHRP research needs statement to develop technical guidelines for critical design considerations in ADAB practices. An Oklahoma DOT research report by Jeong and Abdollahipour (2012) expressed a need to conduct further research to quantify ADAB performance and treatment data for rigid and flexible pavements to better define LCCA models and calibrate assumptions to actual field conditions. As computing and data analysis power continues to increase, the use of a DOT-specific, data-driven LCCA model, such as that used by Texas DOT, will overcome the shortcomings of the assumption-based deter- ministic LCCA procedures currently in use. Leveraging agency-level historical data to populate a stochastic LCCA model, such as the one used by the Ontario Ministry of Transportation, decreases the dependency on professional judgement when conducting an LCCA. A future research project is recommended to assess the costs and benefits of developing a data-driven, stochastic pavement LCC model, and to compare it with the simplified deterministic model in use by Missouri DOT. The final deliverable of the proposed research would be a data-driven framework, based on actual pavement management information system data available in most DOTs, in order to provide pavement engineers with a tool that uses actual local performance data to make pavement-type selection decisions in both conventional and ADAB projects.
