This article proposes Direct Correlation (DC) models and Integrated Correlation (IC) models for cars and motorcycles emissions, respectively. The DC models regress emissions on vehicle-related variables (i.e. direct factors), while the IC models further account for such variables (i.e. indirect factors) as driver/rider demographics, vehicle mileages travelled and regional types by using structural equation modelling. Results show that vehicle characteristics are the most influencing factors affecting hydrocarbon and carbon monoxide emissions. The old vehicles with small engine, manual transmission, high cumulative mileages travelled, using unleaded gasoline #92 and 2-stroke engine (for motorcycle) can be identified as 'high-emitting' vehicles. The second most influencing construct is the driver/rider demographics. The aged, male, low-educated car drivers and motorcyclists with high income and long driving/riding experience tend to use high-emitting vehicles.
- Structural equation modelling