§ 1620. Speed limits on state highways, and on Indian reservations.
(a) The department of transportation with respect to state highways
maintained by the state outside of cities having a population in excess
of one million, and highways on Indian reservations, may by order, rule
or regulation establish higher or lower maximum speed limits at which
vehicles may proceed on or along such highways than the fifty-five miles
per hour statutory maximum speed limit. No such maximum speed limit
shall be established at less than twenty-five miles per hour, except
that school speed limits may be established at not less than fifteen
miles per hour, for a distance not to exceed one thousand three hundred
twenty feet, on a highway passing a school building, entrance or exit of
a school abutting on the highway. Absence of signs installed pursuant to
this section shall be presumptive evidence that the department of
transportation has not established a higher maximum speed limit than the
fifty-five miles per hour statutory limit.

(b) The department of transportation, whenever it determines on the
basis of an engineering and traffic investigation that slow speeds on
any part of a controlled-access state highway maintained by the state
outside of cities having a population in excess of one million
consistently impede the normal and reasonable flow of traffic, may
establish minimum speed limits below which vehicles may not proceed on
or along such highway,

(c) The department of transportation may determine the maximum speed
which may be maintained without structural damage to bridges and
elevated structures that are a part of any state highway maintained by
the state, and, if such maximum speed is lower than the maximum speed
limit otherwise applicable, may by order, rule or regulation establish
such lower maximum speed limit at which vehicles may proceed on any such
bridge or structure.