While constituting a minority of the vehicle population, heavy tractor vehicles have been recognized as significant contributors to air pollution. Despite the existing apprehension, there is a scarcity of published data related to emissions from heavy-duty vehicles on Indian roads, and obtaining real-world measurements of emission factors for regulated and unregulated pollutants is even more challenging. Precise estimation of vehicle activity is of paramount importance for accurately estimating emissions. This paper demonstrates a method for quantifying the emission patterns of NOx, unburned HC, CO, and CO2 coming from diesel tractor vehicles that comply with the Indian emissions standards to evaluate the real-world emissions, and heavy tractor vehicle was tested on different loading conditions using portable emission measurement system. The on-road emission factors (EFs) operating under empty load on trailer and without trailer were compared with the EFs under full load capacity. The analysis revealed that the driving patterns under different loading conditions resulted in increased emissions. Specifically, emissions were approximately 12% higher for CO, 19% for HC, 38% for NOx, and 34% for CO2 when transitioning from empty trailer to a full load capacity. The findings encompass vehicle attributes, acceleration and speed activity profiles derived from real-world data, and potential factors influencing the emissions factor.