From FMCSA website:
"The Federal Motor Carrier Safety Administration (FMCSA) issued a final rule to amend the Federal Motor Carrier Safety Regulations (FMCSRs) to allow the voluntary mounting of certain devices on the interior of the windshields of commercial motor vehicles (CMVs), including placement within the area that is swept by the windshield wipers.
Section 5301 of the Fixing America's Surface Transportation Act (FAST Act) directs the Agency to amend the FMCSRs to allow devices to be mounted on the windshield that utilize "vehicle safety technology."
In addition, section 5301 states that all windshield-mounted devices and technologies with a limited two-year exemption in effect on the date of enactment shall be considered to meet the equivalent-or-greater safety standard required for the initial exemption.
The announcement of this final rule is a nondiscretionary, ministerial action that does not require prior notice and public comment under the Administrative Procedure Act."