A Multidimensional Impact Analysis of Heterogeneous Factors on Mobility of a Multilane Highway

Abstract

In the past few decades, rapid growth in traffic volume has impacted the mobility of multilane highways across the globe. Open access multilane highways have a significant share in the highway network of Pakistan and other developing countries in Asia. These highways have high access density, design inconsistency, and other operational characteristics that differentiate them from partially access controlled multilane highways. Most of the past research on improving highway mobility has focused on controlled access and homogeneous traffic conditions, and as such, open-access highways have been less explored. Mobility of open-access highways, especially in developing countries, is influenced by multiple factors inconsistent with partial or controlled-access environment, which needs to be explored exclusively to accurately predict travel conditions. Therefore, comprehensive research has been conducted to develop a framework to determine combined association of geometric design features, accessibility and numerous mobility influencing factors of open-access multilane highways based on expert opinion, user opinion and in-service road data for mobility management, which is the novelty of this research. A two-phase interview-based questionnaire survey methodology was adopted to explore experts’ and users’ perspectives on mobility performance measures and factors impacting highway mobility. The field data was composed of a video photographic survey collected using the test vehicle method for different categories of open access multilane highways. Mobility performance measure and its influencing factors were selected based on findings of literature review, expert opinion, user opinion and pilot field study. Focus of this research was on microscopic modeling of the straight tangent sections of open access multilane divided highways. A total of seven models have been developed based on different categories of multilane open access highways. Based on the perspectives of experts and road users, speed and travel time were revealed to be the most suitable performance measures for analysis and decision-making on open-access multilane highways. Questionnaire survey results revealed that “heavy traffic” is the most critical mobility influencing factor on open access multilane highways, followed by road width, road condition and access density. It was also revealed that the importance of mobility influencing factors depends upon the performance measure used for analysis. The comparison of rating results between survey groups also disclosed difference of opinions on the impact of different mobility influencing factors on the mobility of open-access multilane highways. xxi Results of multilinear regression revealed that the most significant variable impacting the mobility of open-access multilane highways is access density, followed by the traffic flow and pedestrian crossings. Access density variable was common across all developed models which confirmed that open accessibility in terms of high access density significantly reduces the mobility of open-access multilane highways. The individual models' estimates showed that access density impact is higher on four-lane highways compared to six-lane highways. The analysis revealed that the green belt median is more useful for an engineering design on open access multilane highways rather than only the aesthetics. Moreover, it was found that the change in median type from jersey barrier to green belt is more significant on a six-lane highway compared to a four-lane highway. Findings of this research significantly contribute to the existing body of knowledge related to mobility and accessibility management of open-access multilane highways in developing countries, especially Pakistan. The presented results would provide valuable information to highway agencies, transportation planners, and designers for designing and managing open access highways. Moreover, this study would also help to improve highway design in Pakistan as the developed models included additional mobility-influencing factors compared to previously available models and methodologies. A major contribution of this research is to explore additional factors that influence the mobility of open-access highways but are not included in the level of service methodology. This research presents a comprehensive methodology to evaluate mobility as a measure of functional performance of open access multilane highways in terms of mobility rating, duly accustomed to local travel, road, and traffic conditions, as an appropriate surrogate to exiting LOS methodology with its highlighted inherent grey areas. Another vital and novel outcome of this research is the development of a web based “Mobility Management Tool 2022”. It is a decision support tool based on benefit cost analysis of various mobility improvement intervention alternatives, which would assist highway authorities, designers, and practitioners to make better, calculated and more informed decisions about mobility focused road infrastructure investments and strategy selection, duly cognizant of agency and users’ perspectives.