Indiana Code Title 9. Motor Vehicles § 9-21-5-12

Sec. 12. (a) Except as provided in subsection (d), whenever the Indiana department of transportation determines on the basis of an engineering and traffic investigation that a maximum speed set forth in this chapter is greater or less than is reasonable or safe under the conditions found to exist at an intersection or other place or on part of the state highway system, the Indiana department of transportation may determine and declare a reasonable and safe maximum limit at the intersection or on the part of the state highway system.  The differing limit is effective when appropriate signs giving notice of the limit are erected.

(b) A maximum speed limit under this section may be declared to be effective at all times or at times indicated on the signs.  Differing limits may be established for different times of day, different types of vehicles, varying weather conditions, and other factors bearing on safe speeds.  The differing limits are effective when posted on appropriate fixed or variable signs.

(c) A person who exceeds a speed limit established under this section commits a Class C infraction.

(d) The Indiana department of transportation may decrease the speed limit on a highway in its jurisdiction with a functional classification of minor collector or local road in an urban district to twenty (20) miles per hour without an engineering and traffic investigation.