Zongzhi Li

Highway Project Level Life-Cycle Benefit/Cost Analysis under Certainty, Risk, and Uncertainty: Methodology with Case Study

One of the key steps in the highway investment decision-making process is to conduct project evaluation. The existing project level life-cycle cost analysis approaches for estimating project benefits maintain limited capacity of probabilistic risk assessments of input factors such as highway agency costs, traffic growth rates, and discount rates. However, they do not explicitly address cases where those factors are under uncertainty with no definable probability distributions. This paper introduces an uncertainty-based methodology for highway project level life-cycle benefit/cost analysis that handles certainty, risk, and uncertainty inherited with input factors for the computation. A case study is conducted to assess impacts of risk and uncertainty considerations on estimating project benefits and on network-level project selection. First, data on system preservation and expansion, usage, and candidate projects for state highway programming are used to compute project benefits using deterministic, risk-based, and uncertainty-based analysis approaches, respectively. Then, the three sets of estimated project benefits are implemented in a stochastic optimization model for project selection. Significant differences are revealed with and without uncertainty considerations.

Decision support for optimal scheduling of highway pavement preventive maintenance within resurfacing cycle

This paper presents a case study for optimizing decisions on the best combination of preventive maintenance (PM) treatments and timings to be applied in the resurfacing life-cycle (interval between resurfacing events), for a given highway pavement section. In the optimization procedure, the paper incorporates key infrastructure management concepts of treatment-specific triggers, performance jump models, and performance trend models. Using a case study, the paper determines that optimization can be a viable tool to support scheduling decisions for highway preventive maintenance. Also, using sensitivity analysis, it is determined that changes in the resurfacing interval length and discount rate can influence the choice of optimal PM schedule.

A Heuristic Approach for Selecting Highway Investment Alternatives

A heuristic approach is developed for systemwide highway project selection. It can assess changes in total project benefits using different project implementation options under budget uncertainty and identify the best option to achieve maximized total benefits. The proposed approach consists of a stochastic model formulated as the zero/one integer doubly constrained multidimensional knapsack problem and an efficient heuristic solution algorithm developed using the Lagrange relaxation technique. A method is also introduced to improve the upper bound for the objective function by simultaneously changing multiple Lagrange multipliers. The approach is applied in a computational study to obtain a comprehensive highway investment plan for a State-maintained highway system in the United States.

New Methodology for Intersection Signal Timing Optimization to Simultaneously Minimize Vehicle and Pedestrian Delays

This study introduces a new methodology for signal timing optimization that is carried out by adjusting green splits of a.m. peak, p.m. peak, and rest of the day timing plans for each signalized intersection in the urban street network without changing the existing cycle length and signal coordination to minimize total vehicle and pedestrian delays per cycle. It contains a basic model that handles vehicle delays only and an enhanced model that simultaneously addresses vehicle and pedestrian delays using two different pedestrian delay estimation methods. Both models are incorporated into a high fidelity simulation-based regional travel demand forecasting model for detailed traffic assignments. A computational study is performed for methodology application using data on Chicago metropolitan area travel demand, traffic counts, geometric designs, and signal timing plans for major intersections in the Chicago central business district (CBD) area. A sensitivity analysis is conducted in the application of the enhanced model to examine the impacts of assigning different weights to vehicle and pedestrian delays on intersection vehicle travel time and delay reductions after signal timing optimization. The computational experiment reveals that after systemwide signal timing optimization, vehicle delays in the CBD area could reduce by 13% when considering only vehicle delays and by 5% when simultaneously considering vehicle and pedestrian delays.

Aggregate and disaggregate statistical evaluation of the performance-based effectiveness of long-term pavement performance specific pavement study-5 (LTPP SPS-5) flexible pavement rehabilitation treatments

Engineers continually seek effective techniques for preserving highway infrastructure. Using data from the specific pavement study#5 of the long-term pavement performance (LTPP) programmes western region, this article evaluated the performance of eight flexible pavement rehabilitation treatments. Aggregate and disaggregate post-treatment performance models were developed for each treatment. Effectiveness was measured in the short term (roughness reduction) and long term (estimated treatment service life and area bounded by the performance curve (ABP)). The results showed that compared to 2-inch treatments, 5-inch treatments were on average more effective in terms of the following measures: 47% (estimated service life) and 35% (ABP) depending on the level of surface preparation, mix type and initial pavement condition. Also, relative to minimal surface preparation, intensive surface preparation generally yielded greater effectiveness: 25% (estimated service life) and 49% (ABP) depending on added thickness, mix type and initial pavement condition. Compared to recycled mix treatments, virgin mix was marginally more effective. Finally, compared to pavements treated in poor condition, those treated in good condition were significantly more effective. Treatment effectiveness models were developed for predicting the expected effectiveness of future treatments on the basis of attributes such as treatment type, added layer thickness, level of surface preparation and mix type.

A Hybrid Pareto Frontier Generation Method for Trade-Off Analysis in Transportation Asset Management

Trade-off analysis, one of the key elements of transportation asset management (TAM), helps decision makers to not only quantify how different resource allocations affect system performance but also investigate the trade-off relationships between cost and performance measures and between different performance measures. In the fast-growing field of TAM, researchers are beginning to quantify the trade-offs among the performance measures. A successful quantification of these trade-offs is important for the practice because the highway agency decision makers responsible for project selection have long been stymied by a lack of knowledge of the extent to which different decisions lead to different performance trade-offs. In a follow-up to recent research efforts that have sought to address this issue, this article presents a further improved methodology to facilitate the analysis of trade-offs in TAM. First, a general multiobjective optimization framework for TAM is established. Next, the developed hybrid method is presented, which is then shown to quicken the generation of Pareto frontiers for the purpose of conducting trade-off analysis. Using a case study, the proposed hybrid method, which was implemented on a computer to generate Pareto frontiers, ultimately converged faster and generated better-distributed Pareto frontiers compared to the NSGA II method of Pareto frontier generation in the TAM context. Using the generated Pareto frontiers, trade-off analysis between cost and performance measures and between performance measures are demonstrated in this article.

Methodology to Determine Load- and Non-Load-Related Shares of Highway Pavement Rehabilitation Expenditures

A marginal cost method for quantitative assessment of the load- and non-load-related shares of pavement rehabilitation expenditures is described. A set of ordinary least-squares models was formulated by an aggregate approach. The study revealed that the shares of pavement rehabilitation expenditures attributable to load factors depend on pavement type, year of study, and other variables. The load- and non-load-related fractions of rehabilitation expenditures used to repair pavement damage were found to be 28 and 72 percent, respectively, for flexible pavements, 78 and 22 percent, respectively, for jointed concrete pavements, and 38 and 62 percent, respectively, for composite pavements. It is expected that the results of the study will facilitate the apportionment of pavement rehabilitation expenditures for highway cost allocation in a fair and equitable manner.

Life-Cycle Cost Analysis of Highway Intersection Safety Hardware Improvements

A methodology is proposed for project-level life-cycle cost analysis of highway intersection safety hardware improvements. It incorporates a disaggregated risk-based approach for computing the safety index that could be used to assess intersection vehicle crash risks affected by the conditions of intersection safety hardware such as signs, signals, lighting, pavement markings, and guardrails. With safety indices estimated before and after implementation of an intersection safety hardware project, the annual potential for safety improvements (PSI) could be computed using the concept of consumer surplus. The annual PSI is further converted into dollar values and extrapolated to the overall intersection safety hardware service life cycle, defined as the useful service life of longest-lasting intersection safety hardware, to determine the maximum project-level life-cycle benefits of intersection safety hardware improvements. A computational study is conducted for methodology application and validation using 5-year data on 226 intersections in Ozaukee County, Wis. The proposed methodology could be adopted by state and large-scale local transportation agencies for intersection safety hardware project evaluation and investment decision making.

Modeling traveler mode choice behavior of a new high-speed rail corridor in China

This study examines mode choice behavior for intercity business and personal/recreational trips. It uses multinomial logit and nested logit methods to analyze revealed preference data provided by travelers along the Yong-Tai-Wen multimodal corridor in Zhejiang, China. Income levels are found to be positively correlated with mode share increases for high-speed rail (HSR), expressway-based bus, and auto modes, while travel time and trip costs are negatively correlated with modal shift. Longer distance trips trigger modal shifts to HSR services but prevent modal shift to expressway-based auto use due to escalation of fuel cost and toll charges. Travelers are less elastic in their travel time and cost for trips by nonexpressway-based auto use modes. The magnitude of elasticity for travel time is higher than trip costs for business trips and lower for personal/recreational trips. The study provides some policy suggestions for transportation planners and decision-makers.

Project-Level Life-Cycle Benefit–Cost Analysis Approach for Evaluating Highway Segment Safety Hardware Improvements

This paper presents a methodology for a benefit–cost analysis of improving the conditions of highway segment safety hardware over its life cycle. In the framework, a safety index is established for assessing the risks of vehicle crashes on a highway segment. These risks are associated with the safety-related attributes of the segment, which include traffic volume, segment length, standards and consistency of geometric design, pavement surface condition, safety hardware condition, and roadside features. The annual potential for safety improvements (PSI) associated with safety hardware improvements is calculated as reductions in fatal, injury, and property-damage-only crashes on the highway segment on the basis of the without- and with-improvement safety indices. Then, by monetizing and extrapolating the annual PSI over the longest hardware service life, the maximum life-cycle benefits of safety hardware improvements for the highway segment are established. To demonstrate the application of the methodology, data on 193 highway segments in Ozaukee County, Wisconsin, are collected and analyzed and the results are validated using the root-mean-square error test, chi-square test, Spearmans rank correlation test, and the Mann–Whitney test. A direction for future research is recommended to simplify the methodology and to prepare guidelines for enhancing its practical implementation.