This study compares the results of three on-road chasing campaigns conducted in 2011, 2017, and 2023, making it the first to report how real-world emission factors (EF) for diesel vehicles have changed over a decade. By directly measuring emissions during real-world driving, this research provides critical insights into the effectiveness of emission control technologies and regulatory interventions. The findings highlight the transformative impact of Diesel Particulate Filters (DPFs), which have consistently reduced black carbon (BC) EF from diesel vehicles to levels comparable to gasoline-powered cars. This underscores the success of DPFs in controlling particulate emissions, a major contributor to air quality issues. Real Driving Emissions (RDE) regulations have also proven effective in significantly lowering nitrogen oxide (NO<sub>x</sub>) emissions. By incentivizing the use of previously underutilized technologies, these regulations ensure better compliance with standards during typical driving conditions. Real-world EF measurements are crucial for bridging the gap between ambient pollution data and traffic emission models, enabling more accurate assessments of vehicle fleet contributions to air quality. This study employs an independent chasing method, demonstrating its value as a practical tool for monitoring fleet emissions, identifying super-emitters, and detecting vehicles with defeat devices. Overall, this decade-long analysis highlights the significant advancements in reducing diesel emissions, while emphasizing the importance of sustained efforts in monitoring and regulation to further improve air quality and refine emission modeling frameworks.