When an expressway renovation and expansion project involves a long steep-grade segment, the vehicle operating conditions are influenced by the overlapping impacts of the roadway environment and construction activities, thereby affecting traffic safety and efficiency. Hence, there is an urgent need for a quantitative assessment of traffic operations under the combined scenario of renovation construction and long steep-grade road sections. In this paper, four key indicators—time occupancy, traffic density, speed consistency, and travel delay—are first selected to characterize driving risk and operational efficiency. Subsequently, multiple simulation scenarios are established in VISSIM under varying work zone lengths and large vehicle proportions, and the resulting data are evaluated via gray relational analysis. Finally, based on the variation trends of these indicators and the ranking of gray relational coefficients, we propose optimization recommendations for construction traffic management from the perspectives of work zone layout, lane management, and speed limit control. The results show that: with a relatively short work zone length and a large vehicle proportion not exceeding 30%, travel delay and speed fluctuations remain small, and the overall traffic performance surpasses that of other configurations; as the large vehicle proportion and work zone length increase, time occupancy and the standard deviation of speed both rise markedly, presenting a dual adverse situation of high risk and low efficiency; under conditions where both the large vehicle proportion and the construction scope expand, speed consistency becomes the most significantly affected factor, necessitating close attention to the amplified speed gap caused by heavy vehicles’ reduced climbing speeds.