According to Digital Signage Today, several states in the US have recently adopted standards for controlling the set up and operation of digital signage boards along highways. As an example, they quote the recent adoption of new legislation in Colorado.
So far 12 states and Puerto Rico have passed legislation to control outdoor signage in regards to brightness and other restrictions along highways. One of the key regulations is the brightness issue to avoid startling drivers with high brightness signs. As they conclude, the Colorado legislation is very similar to the laws of other states addressing this issue.
Source: Digital Signage Today
You can find more information on the different state laws at the respective sites for Colorado, Massachusetts, Michigan, New Mexico, Oregon, Tennessee, and Wyoming. Digital Signage Today sees the Colorado legislation as typical for these new state laws. As the highways are a kind of federal transportation system, they still fall under regulation by each state for the portion that is in the respective state.
Since the the federal government is funding the maintenance of the highway system, it is requiring states to comply with certain federal laws and guidelines such as the Highway Beautification Act, but also safety standards. In case a state does not comply with federal laws or does not enforce these laws, the federal administration can withhold up to 10% of the highway funding. In the case of Colorado, this would have equated to $40 million per year. This money would have to come out of the state budget instead, providing a strong motivation for the states to pass these compliance laws.
The Colorado law addresses a variety of issues with highway signs. First of all it only addresses signs that are close to highways and are within 660 feet (200 m) of the nearest edge of the highway. Other signs that are further away or on private property do not fall under this jurisdiction unless they violate certain restrictions about location and size. There is also a restriction on the number of signs on the side of a highway.
A Changeable Electronic Variable Message Sign (CEVMS) or digital billboard/sign requires not only a permit but is also restricted in its peak brightness to avoid blinding the passing driver. To be fair, also non-digital signs are restricted in that they cannot blind drivers by using blinking or steady lights. The law allows the sign to only produce an illuminance of 0.3 foot candles (3.2 lx) above ambient before sunrise or after sunset. The measurement has to be taken at a certain distance that depends on the size of the sign itself. If the sign does not comply with this measurement, the nighttime luminance shall not exceed 300 cd/m².
There is also a provision that the brightness of the sign may not be altered in intervals of less than 4 seconds and updating the content cannot have transitions intervals of less than 1 second. Te use of full motion or intermittent video content is also specifically disallowed. – NH
