Driving is a primary task that requires full attention. However, several factors could cause distractions and affect the attention of drivers. Distractions come from both internal and external sources. Internal distractions happen when a person engages into distracting activities inside the vehicle (Beanland et al., 2013) while external distractions come from outside of the vehicle wherein there is a delay in recognition of information needed to safely accomplish the driving task because there are events, activities, object, or person outside the vehicle that tend to induce the driver to shift his attention away from the driving task (Regan et al., 2011). Both external and internal distractions contribute to the interference of focus (Post, S., Schumm, J., 1997). Thus, this paper aims to analyze contributing factors in internal and external sources that affect the attention of drivers in the Philippines. Design of Experiment (DOE) has been used to simulate a model for driving performance of subjects to determine the effect or impact of factors in internal and external sources to the attention of drivers. Contributing factors of internal sources that were considered in the study are tasks, age, gender, driving experience and type of license used by drivers while factors for external sources include pedestrian crossing, vehicle cuts-in, vehicle emergency brakes and vehicle counter flows.  On the other hand, measurements on the impact of driving performance that were considered in the study are change in speed, lane departure and collision count. Statistical analyses such as analysis of variance and Cramer’s V test were employed in the study to determine the relationship of contributing factors to the impact of driving performance. The results of the study showed that among the contributing factors in the internal sources, eating while driving has the highest impact on the driving performance of subjects while for external sources, all contributing factors have significant impact on the driving performance of subjects. Therefore, the result of the analysis will serve as the basis for the researchers to propose policies and regulations to help drivers avoid driving distractions and ensure road safety.