Evaluation of Sustainable Design Method for Three-Lane Entrance Ramps on Expressways in Urban Areas: A Case Study of Xi’an, China

Owing to the challenges faced by two-lane entrance ramps in merging areas on expressways in handling the growing traffic volume, designers are considering implementing three-lane entrance ramps. This approach alleviates capacity bottlenecks and facilitates efficient, safe, and green operations. However, according to the traditional design strategy, the long auxiliary lanes will bring large land occupation and construction consumption, creating obstacles to the reconstruction. To address this issue, this study proposes two new strategies and discusses the applicability of each scheme. A VISSIM microsimulation model was developed and calibrated using the collected data, and five evaluation indicators assessing environmental protection, capacity, traffic efficiency, safety, and construction consumption were selected. This study also presents a comprehensive evaluation(CE) method that combines the CRITIC (Criteria Importance Through Intercriteria Correlation) method and TOPSIS(Technique for Order Preference by Similarity to an Ideal Solution), which considers the association between indicators and offers a more rational evaluation, aiming to recommend optimal designs for various traffic cases. The results indicate that two-lane ramps are still the preferred choice for lower traffic volumes and merging ratios, whereas three-lane ramps demonstrate excellent potential for application under heavy traffic conditions. The CE reveals substantial improvements in optimal designs, with capacity, delay, CO emissions, and conflicts showing maximum enhancements of approximately 20%, 45%, 5%, and 55%, respectively.