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requires only that messages be changed at "reasonable intervals."' Moreover, the U.S. Small Business Administration, in a report on its website reviewing safety information compiled since the 1980 report, has concluded that there is no adverse safety impact from the use of EMD signs. See htto://www.sba qov/starting/signage/safelegal html. The most recent study was performed in 2003 by Tantala Consulting Engineers, available through the U.S. Sign Council at http://www.ussc.org/publications.html, also concluding based on field studies that EMD signs do not adversely affect traffic safety. Many small businesses using one-line EMD displays are only capable of displaying a few characters at one time on the display, changing frequently, which takes virtually no time for a driver to absorb in short glances. These signs have likewise not proven to be a safety concern, despite many years of use. 4. Operations: Total information cycle. EMD signs can be used to display stand-alone messages, or messages that are broken into segments displayed sequentially to form a complete message. As to the sequential messages, the report recommended a minimum on-time for each message "calculated such that a motorist traveling the affected road at the 85'h percentile speed would be able to read not more than one complete nor two partial messages in the time required to approach and pass the sign." 5. Operations: Duration of message change interval and off-time. The report defines the message change interval as the portion of the complete information cycle commencing when message "one' falls below the threshold of legibility and ending when message "two" in a sequence first reaches the threshold of legibility. This is relevant when operations such as "fade off-fade on" are used, when the first message dissolves into the second message, or when the two messages move horizontally (traveling) or vertically (scrolling) to replace the first message with the second. Off-time, on the other hand, is a message change operation that involves the straightforward turning off of the first message, with a period of blank screen, before the second message is instantly turned on. ~ The appropriate interval of message change may be affected by a variety of factors, and one standard does not fit all situations. Imagine, for instance, a bridge that serves two roadways, one with a speed limit of 30 mph and the other a highway with a speed limit of 60 mph. in a situation where the bridge is socked in by fog, an electronic sign on the approach to the bridge may be used to convey the message, "Fog ahead...on bridge...reduce speed... to 15 mph." The driver on each roadway needs to see all the segments to the full message. Tlie rate of changing each segment of the message needs to be different for each roadway. If the change rate were based only on the 60 mph speed, the sign on the slower roadway may appear too active. if the change rate were based only on the 30 mph speed, the result could be i'atal to drivers on the highway,_ 6 26-