Sec. 6. (a) Except as provided in subsection (b), a public or private agency may not erect a traffic control device on a state maintained highway without the written permission of the Indiana department of transportation.
(b) This subsection applies to the installation of traffic signals on a state highway in a city or town. The Indiana department of transportation shall:
(1) install any signal that meets the standards, specifications, and warrants set forth in the Indiana Manual on Uniform Traffic Control Devices for Streets and Highways; or
(2) grant written permission to a city or town to erect the signal if it is not possible for the state immediately to install the signal.