Adaptability evaluation of the upgraded highway's geometric alignments based on speed-related characteristics: A case study

Upgrading Class I highways (i.e., divided highways without access control) to freeways (i.e., divided highways with full control of access) is a common method of freeway construction in China. This study investigates whether or not the geometric alignments from the Class I highway can adapt to the high speed traffic on the upgraded freeway by taking the highway from Ning'an to Fuxing in Heilongjiang Province as a case. Traffic conditions before and after the upgrade are video-recorded and then the traffic flow and operating speed data are extracted from the video. The acceleration data after the upgrade is measured by using a vehicle-mounted triaxial accelerometer. Based on the data collected, the adaptability of the upgraded freeway's geometric alignments is evaluated from the aspects of safety and comfort, and the quantitative criteria include design consistency and operating speed consistency for safety evaluation, and side friction factor and vertical acceleration for riding comfort evaluation. The evaluation results show that the overall performance of the geometric alignments is good after the upgrade, but sections with strict geometric limits perform slightly poorly.