However, the use of advanced communication technologies such as cellular communication does not automatically resolve all the issues we encounter in real-time traffic scenarios. For example, on urban roads where vehicle density increases significantly during peak hours, maintaining seamless communication under quality of service (QoS) constraints becomes a critical challenge. Traditional orthogonal multiple access (OMA) schemes, which allocate distinct channels to each user, often struggle with channel scarcity in high-density environments. To address this challenge, we explore non-orthogonal multiple access (NOMA) as a potential solution. NOMA enhances spectral efficiency by enabling multiple users to share the same channel simultaneously, distinguishing each user's signal through power domain differentiation rather than unique encoding schemes. Using a technique called successive interference cancellation (SIC), the receiver can separate and decode the composite signal, effectively managing interference and allowing more efficient use of limited channel resources. Capable of accommodating more users compared to traditional OMA, NOMA is treated as a promising solution for high-density scenarios. Integrating NOMA into vehicular communication systems is expected to enhance the overall network performance and QoS [3]. NOMA is becoming a practical and indispensable solution for real-world applications, including cellular communication (i.e., multi-user superposition transmission or MUST) and digital TV (i.e., layered division multiplexing or LDM) [4]. In addition to the channel scarcity with high user density, high energy consumption for communication is another urgent challenge to overcome especially in the vehicular communication domain [5; 6]. Wireless access networks are projected to consume approximately 446 TWh of electricity in 2030, which is approximately four times greater than what it is in 2024, i.e., 102 TWh [7]. High consumption of energy can result in an increase in greenhouse gas emissions and operational expenditures (OpEx) of the mobile network operators (MNOs). In the case of intelligent transport systems (ITSs), wireless nodes can be embedded in battery-operated road signs and traffic control devices [5]. Poor power transmit power management schemes can quickly deplete these batteries. Even in the case where roadside units (RSUs) with stable power supply are utilized for communication, careless transmit power control may lead to a violation of QoS requirements. While power usage is indeed a fundamental aspect of wireless networks, we aim to emphasize its specific importance within vehicular networks, where devices often rely on limited battery resources and operate in energy-constrained environments. Efficient power management is essential to maintaining continuous communication in dense urban settings with high energy demands. In this regard, this study focuses on how to optimally utilize NOMA downlink to accommodate more VUs while minimizing transmit power consumption to guarantee reliable and energy-efficient communication in crowded urban traffic environments. Downlink communication is critical in vehicular networks, as it may enable RSUs to provide vehicles with safety-related real-time information such as traffic alerts, road conditions, and navigation updates. NOMA for downlink has been widely studied and also it has demonstrated substantial benefits in enhancing spectral efficiency, reduced latency, and support for massive connectivity, its real-time application in vehicular networks introduces critical challenges, particularly regarding resource optimization [8; 9]. In addition, NOMA introduces intra-cell and intra-cluster interference, which increases the complexity at the receiver end compared to conventional OMA [9]. Moreover, poor user clustering can pose a critical hurdle to enhancing system throughput [4; 9; 10; 11]. [PERSON] et al. [12] show that NOMA outperforms OMA in terms of sum rate and transmit power consumption.