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 work zones, traditional countermeasures often fail to prevent crashes. As such, smart warning systems could be very helpful in notifying drivers about upcoming conditions within work zones. In this study, a smartphone-based warning system was designed to investigate the effectiveness of advanced warning and notifications on the reduction of forward collisions in a work zone. Four different warning messages were prepared (visual, sound, male voice and female voice) to alert drivers. Driving simulator tests with eighteen participants, driving through a work zone for ninety rounds, were conducted to investigate the impact of smart-phone based warnings on performance measures, including 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 rate and speed were significantly lower; and headway time and distance were significantly longer. The sound and voice warnings are beneficial to the reduction of total vehicle emissions. Moreover, participants found the notification system being user friendly and helped to avoid rear-end crashes in work zones.