Miss. Code Ann. § 63-3-503

Whenever the state highway commission shall determine upon the basis of an engineering and traffic investigation that any speed set forth in Section 63-3-501 is greater than is reasonable or safe under the conditions found to exist at any intersection or other place or upon any part of a highway, said commission shall determine and declare a reasonable and safe speed limit thereat which shall be effective when appropriate signs giving notice thereof are erected at such intersection or other place or part of highway.

Whenever the state highway commission determines that speed limits set forth in Section 63-3-501 are different from those speeds set forth in applicable laws of the Federal Government, then said commission may declare a speed limit which is consistent with such laws and which shall be effective immediately upon adoption by the commission. Appropriate signs giving notice of the adopted speed limits shall be erected upon order of the commission.

The maximum fine and sentence to be imposed for a violation of excessive speed above the maximum limits set by the state highway commission pursuant to the authority granted by this section shall be one-half ( 1 / 2 ) the fine and sentence imposed by Section 63-9-11 if the excessive speed does not exceed the maximum limits imposed by Section 63-3-501 .