Some systems offer an Optical Compatible GPS system with features that also include an Inertial measurement unit (IMU). The price point of some compare to Optical Systems. Therefore, cities that do not have preemption can get a GPS based system for the price of Optical Systems (typically 1/3 the price of many GPS systems). Additionally, cities that have existing optical systems can start upgrading to a GPS-based system while maintaining compatibility with their existing Optical vehicle emitters. These systems also come with Collision Avoidance.