A system and method for warning vehicle operators of obstructions are provided. First clearance data of the vehicle, including vehicle height and width, are obtained and stored in memory. An obstruction in the vehicle's path and the travel surface between the vehicle and the obstruction are scanned by a sensor device. Second clearance data of the obstruction, including the height and width of the vehicle passage defined by the obstruction, are determined and are stored in memory. Utilizing a comparison/warning signal generating device, the first and second clearance data are compared, and a warning signal is generated when values of the first clearance data are equal to or greater than corresponding values of the second clearance data. A monitoring device monitors the time period between generation of the warning signal and responsive action by the vehicle operator to avoid a collision. The vehicle is automatically brought to a stop if, upon expiration of a preselected time limit, the vehicle operator has not taken appropriate action.