Collisions in work zones have always been a contributing factor in compromising safety on urban roadways. National Highway Traffic Safety Administration (NHTSA) and State Transportation Authorities have implemented many safety countermeasures to reduce forward collision in work zones. However, due to the complexity of traffic in a work zone, traditional countermeasures often fail to prevent crashes. As such, smart warning systems can be applied to notify motorists about upcoming conditions in work zones. In this study, a smartphone-based warning system was designed to investigate effectiveness in reducing forward collisions thru advanced warning and notifications about a work zone. Four different warning messages were generated (visual, sound, male voice and female voice) to alert drivers. Driving simulator tests with eighteen participants with ninety rounds thru work zones were conducted to investigate the impact of smart-phone based warnings on performance measures such as: headway distance, headway time, speed deceleration, and emissions. Statistical results show that, with the help of voice (either female or male) warnings on forward collisions, acceleration and speed was reduced, and headway time and distance increased. Results also showed that sound and voice warnings also reduced total vehicle emissions. Moreover, participants found the notification system user friendly and felt it helped to avoid rear-end crashes in work zones. Overall, this low- cost and effective smartphone application should be tested in real road conditions with similar safety measures as employed in this paper.