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Emission-controlled pavement management scheduling
U.D. Tursun, R. Yang & I.L. Al-Qadi
University of Illinois Urbana–Champaign, USA
ABSTRACT: This paper describes an analytic approach that can be used to evaluate and propose rehabilitation schedules based on economic, performance, and environmental considerations for various types of pavements managed by the Illinois State Tollway Authority. A Mixed-Integer Nonlinear Program (MINLP) is formulated to model the agency’s life-cycle cost and environmental impacts where the decision set consists of the maintenance overlay type and the thickness of the overlay proposed on a temporal scale over a planning horizon. The problem requires interaction of the integer and continuous variables that leads to MINLP formulation. Considering practical implications of the problem, the continuous variables are bounded into a finite and discrete set, while the integrality constraints are relaxed. The objective and constraints of the problem can be alternated to suit the needs of the agency, which may be interested in minimizing environmental impacts and restricting the cost to the agency, or vice versa, over the pavement life-cycle.
Keywords: Mixed-Integer Nonlinear Programming, Sustainability, Pavement Management
1 PAVEMENT MANAGEMENT SCHEDULING
1.1 Introduction
Although transportation agencies traditionally have considered cost as the main factor in deciding initial pavement design and maintenance schedules, interest in evaluating environmental impacts of transportation infrastructure has become common. In a 2011survey, it was found that 29 out of 35 responding state Departments of Transportation (DOTs) in the United States perform Life-Cycle Cost Analysis (LCCA) to evaluate alternative pavement designs for new construction and reconstruction projects (Hallin et al. 2011). Thus, both the initial cost of construction and the future cost of expected Maintenance and Rehabilitation (MR) schedules over the lifetime of the pavement are considered.
The parallel approach to LCCA for environmental consideration is Life-Cycle Assessment (LCA), which is not currently implemented by any US state DOT. Similar to LCCA, this methodology evaluates the environmental impacts incurred over the entire pavement life cycle from initial construction, MR, use, and disposal. If combined, LCCA and LCA result in quantitative cost and environmental measures, respectively, that can systematically inform an agency’s decision-making process.
As LCCA is already an established component of pavement management, recent literature has investigated the application of LCA to pavement management and, specifically, how cost and environmental concerns can be balanced. Gosse et al. (2012) used a multi-objective genetic algorithm able to develop Pareto sets of maintenance plans in Virginia for various budgets, pavement performances, and emission levels. The scope of the work included only materials and construction, taking into account the deterioration of the pavement without user emissions or costs. Yu et al. (2013) further integrated LCA and LCCA for three types of overlay systems by using dynamic programming to consider both agency and user emissions, as well as costs from construction, work zone delay, and normal use of the pavement. Optimized strategies for each overlay system were developed by minimizing life-cycle cost, as well as environmental impacts (greenhouse gases, GHGs; and energy). Lidicker et al. (2012) in turn evaluated resurfacing policies based on minimizing life-cycle costs and emissions from both the user and the agency to find optimal overlay intervals (i.e. 15 years for minimum GHGs and 22 years for minimum cost).
Bryce et al. (2014) and Reger et al. (2014) applied optimization techniques at a multifacility level, incorporating pavement segments from a large network. Bryce et al. included various levels of MR treatment types, and also incorporated probabilistic distributions to account for uncertainties in the extent of treatment (e.g. thickness of overlays), transportation distances, and per unit environmental impact values themselves. A Pareto set for a network was given with respect to cost, energy, and pavement condition. Reger et al. minimized equivalent annual agency costs for a network while constraining GHGs. A Pareto set was formed and used to evaluate past and present MR policies in California. An updated study by Reger et al. (2015) also considered constraining the agency budget and minimizing emissions. In the network-level studies mentioned, delay effects from the work zone during construction was omitted.
Overall, a number of approaches have been implemented to integrate economic and environmental concerns into pavement management. However, this study extends the literature by including probabilistic consideration of changing traffic levels over time, updated inventory, an...
