Researches indicate that foggy weather is one of the most critical factors that restrict human’s traffic activities and cause traffic accidents. It will reduce the visibility of traffic message board, which could cause the insecurity of transportation. Commonly, light-emitting diodes (LEDs) were used as light source for variable message sign, which could not be seen clearly in the foggy low visibility condition. A high-brightness light source which could be used for variable information board was firstly put forward in this paper. And a new type of variable message sign used in low visibility condition was also introduced. Besides, the attenuation characteristics of laser diode (LD) and light-emitting diode (LED) were analyzed respectively. Calculation and simulation show that the attenuation of red light source is fastest, and the yellow LED light has the better transmittance property. In the experiment, LDs were used to make variable message board for verifying image definition. A 16*16 array structure composed of LDs was designed and could display Chinese characters. By comparing the display effect of LDs and LEDs driven with same power, they were placed in fog chamber of the visibility less than 5 meters. And experiment results show that the penetrability of red LD light is better than that of red LED. So traffic variable message sign based on LDs could improve the image definition and the information could be seen more clearly in the foggy weather. In addition to the high-brightness, good coherence, good direction, experimental results show that traffic variable message board based on LD has better visual effect in low visibility condition.