This document describes a study that proposes and tests a smartphone-based system to warn drivers about upcoming horizontal curves in the road. The system uses the smartphone's GPS, Bluetooth, and computing abilities to track a vehicle's speed and position in real-time and compare it to curve location data. When approaching a curve, the smartphone sends a warning message via Bluetooth to a display unit on the vehicle's windshield. The study involved defining requirements, testing the system architecture under various scenarios, improving the warning algorithm, and evaluating the system's speed/location accuracy and ability to detect curves through field tests.