This article investigates the effects of aerodynamic and lightweight double-deck semi-trailers on fuel consumption of Heavy Goods Vehicles (HGVs). The HGVs were evaluated using in-service data, and computer-based simulations with coefficients of aerodynamic drag and rolling resistance estimated from coast-down tests conducted on a test track. The coast-down tests showed that the aerodynamic features reduced the coefficient of aerodynamic drag by approximately 7.2% and the wide single tyres on the lightweight trailers reduced the coefficient of rolling resistance by approximately 10%. The in-service data showed that the aerodynamic features on the aerodynamic vehicles have a statistical significance on fuel consumption. Computer-based simulations showed that the aerodynamic-lightweight trailer reduces the HGV's fuel consumption by approximately 20.2% for a long-haul drive cycle. As these improvements don’t have significant barrier to implementation, which is the case with electrification of HGVs, fleet operators can employ these improvements to reduce their carbon emissions.