It shall be unlawful to excavate or disturb the shoulders, ditches, embankments or the surface improved for travel of any class I or class III highway or state-maintained portion of any class II highway for any purpose whatever without written permission from the commissioner of transportation or his district engineer, or any other highway without written permission from the selectmen or highway agent of the town, or the mayor and aldermen or street commissioner of the city; provided that in cases of emergency where the public health or safety is endangered such immediate action as may be necessary may be taken without such permission, but in such cases the person directing or taking such action shall at once notify the official empowered to give written permission.