What does it mean when the yellow lights are flashing on the road signs?

 When the yellow lights are flashing, it indicates that there is a message being broadcast. On this message, could be information on construction, emergencies and traffic incidents. This information can also be found on the Thruway's Highway Advisory Radio(HAR)stations. See link below.

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NYS Thruway Authority
Information about the NYS Thruway and Highway Advisory Radio
URL: http://www.thruway.ny.gov/travelers/har/index.html