This book comprised with two test studies which were conducted by using smartphone based message in workzone area. In both studies, tests were performed with 24 participants by using driving simulator. Two Smartphone based apps, Safe Forward Collision Warning (SFCW) and Safe Worker to Driver (SWD) were developed by using MITapp inventor 2. In the first test, participants were travelled advanced warning area with four (visual, sound, male and female voice) different kinds of warning messages generated to inform the accident at the end of the advanced warning area. Similarly in the second test, three (sound, male and female voice) warning messages were developed to inform driver about the worker crossing in activity area of work zone. In these two tests, obtained data from driving simulator test, was analyzed and compared with the base scenario. These test results and statistical analysis indicated that participants with voice warning, either male or female voice warning, were successfully able to reduce their speed and acceleration in both tests. Participants were able to increase their headway distance and headway time and applied earlier brake with the assist of voice warning.