Improved processes for selection and design of lightly surfaced roads
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This research begins by conducting case study research to determine the current practices of applying Light Surface Treatments (LSTs) on aggregate-surfaced roads in Minnesota. Based on the results of the case study research, a selection guide is developed to select which aggregate-surfaced roads are good candidates for LSTs. The selection guide considers factors such as traffic volume and traffic type, sub grade and sub-base conditions, availability of quality of aggregate and costs of alternative methods for treating aggregate-surfaced roads. The selection guide will include both a GIS model and a decision tree. The GIS model can be used by road officials to make a preliminary assessment to find which roads have the characteristics of a candidate road. Once roads or areas have been identified using the assessment, the decision tree can be used to confirm or refute whether the road is a candidate road. The roads identified by the selection guide were validated using both Henning's (Henning, Bennett, & Kadar, 2007) model and interviews of county engineers. This paper concludes that both Henning's model and the county engineers validated that this selection guide can be used to identify candidate roads. Additionally, the model that was developed can be applied to a number of counties and states in the United States because the requisite GIS data is widely available.
The second part of the research provides recommendations to improve the current practices used to design the road structure supporting a LSTs. Throughout the literature review, it was found that the majority of low-volume road officials in the United States use pavement design methods to design the road structure for an LST. Minnesota was selected as a case study to investigate the current practices of low-volume road officials. In Minnesota the Gravel Equivalent method, the Mechanistic Empirical method and the AASHTO method are the methods used to design roads with LSTs. These three methods were used to design a stabilized full depth reclamation layer on two case study paved roads in rural areas in Minnesota. The case study road designs show that each method has shortcomings that noticeably affect the road design. It is recommended that low-volume road officials throughout the United States conduct a similar evaluation of the design methods used to design their road structure of LSTs. After these shortcomings have been identified, actions should be taken to address the shortcomings. In conclusion, the research found that a design method should be developed to design the road structure of LSTs specifically for local conditions found in each state of the United States. This design method should be straightforward to implement so it compatible with the workload of a local transportation official and should consider factors such as climate, various surface layers, ESALs and soil support conditions.