The ODOT research project using UAVs to conduct bridge inspections will be posting warning signs to alert drivers to the activity in the area. This will likely be a common practice when the technology is used in areas that might bring the UAV in fairly close proximity to the roadway. It seems reasonable to consider how drivers respond to such warnings, which generally are in the form of a variable message sign (VMS).
Charleton (2006) found that the effectiveness of road works/hazard signing depended on the type of hazard sign used. Perhaps surprisingly, this study found that a flashing variable message was "only slightly more conspicuous than the large dimension format, equal in comprehensibility, and perhaps somewhat worse in terms of memorability." Another study examined the effect of using a VMS to issue a warning, followed shortly by a variable speed limit sign (VSL). The results showed that drivers were much more responsive to the reduced speed when the VMS warned of dangerous driving conditions or potential hazards rather than a speed enforcement notice (Lee and Abel-Aty, 2014). Kircher and Thorslund (2009) examined the impact of low friction warnings during icy conditions. Without the warning, drivers varied speed based on whether or not ice was visible. Since icy conditions can be invisible, this was a serious safety concern. The study showed driver response and compliance with low friction warning signs, even when ice was not visible.
On the other hand, a survey of drivers' response to variable message signs in London showed that only one third of drivers saw the posted information, and few of those reacted to it, in terms of diverting to another route or changing driving practices. The survey also noted that the location of the warning and the message content were important factors in determining drivers' awareness and response. (Chatterjee et al., 2002).