PURPOSE: To improve the driving safety of vehicles by forming guide lines on the surface of a road by projecting a molten gaseous jet of a metal which can be detected with a metal detector and attaching metal detectors, a laser detector, an alarm, etc., to the vehicles and issuing alarms when the vehicles meander across the guide line, abnormally approach preceding vehicles, and so on.

CONSTITUTION: Guide lines 10 and 10' are formed on the surface of a road by projecting a molten gaseous jet of a metal which is obtained by melting a metallic wire with an arc torch. On the other hand, metal detectors 14, 16, 18 and 20 and a laser detector 22 which detects the distance to a preceding vehicle are installed to an automobile 12 and a controller and an alarm are installed to the driver's cabin of the automobile 12. When the automobile 12 crosses the guide line 10 or abnormally approaches the preceding vehicle, a warning alarm is issued by means of a buzzer, lamp, etc. Therefore, the meandering or collision of the automobile 12 resulting from drowsy driving, etc., can be prevented.