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With considerable population and high emission rates, tri-wheel vehicles contribute to significant pollution throughout China. The first-phase and second-phase emission standards for rural vehicles were introduced in 2006 and 2007. However, the effectiveness of the standards is unknown due to the lack of relevant research. In this study, a Portable Emission Measurement System (PEMS), which is comprised of a regulated gaseous emission analyzer (SEMTECH-DS) and an electrical low pressure impactor (ELPI), was introduced to characterize the emissions of tri-wheel vehicles in real-world operating conditions. Carbon monoxide (CO), hydrocarbons (HC), NOx and PM emissions of 10 tri-wheel vehicles were measured on planned routes, which contained both national roads and rural roads. The results showed that on national roads, there were fewer acceleration and deceleration circumstances than on rural roads. Most of the emission peaks appeared in the acceleration mode. Among the three driving modes (acceleration mode, deceleration mode and cruising mode), distance-based emission factors of CO, HC, NOx and PM for acceleration mode were the highest on national roads and rural roads. For the acceleration mode on national roads, the average distance-based emission factor of CO was 0.7 times greater than in cruising mode and 1.7 times greater than in deceleration mode. Average emission factors of CO, HC, NOx and PM for each driving mode on rural roads were higher than that on national roads. By drawing contour maps of speed, acceleration and pollutant-emission rates, we found that pollutant emission peaks of CO, HC and PM increased at low speed and under high acceleration conditions on both national roads and rural roads. Emission rates of NOx on rural roads were higher than those on national roads. The number-weighted distributions of particles on national roads and rural roads were similar. Most of the particles were in the nuclei mode and the accumulation mode. Number concentrations of coarse-mode particles on rural roads were higher than on national roads. This paper could provide some reference for future emission controls for tri-wheel vehicles. [ABSTRACT FROM AUTHOR]