## 2 Roadway Signage and Human Factors Issues  
Roadway signage is one of the most common forms of traffic control device. Signs utilize words, pictorial elements, or a combination of these to convey information [17]. Although extensive design guidelines have been developed for roadway signs [18], these guidelines do not apply to ensuring readability and comprehension of signage information when presented via an in-vehicle display. [PERSON] and [PERSON] identified five ergonomic principles related to the development of traffic signs, including: (1) spatial compatibility, (2) conceptual compatibility, (3) physical representation, (4) familiarity, and (5) standardization. Spatial compatibility refers to a sign's physical position and orientation in space [19]. For example, in a right-side driving environment, a stop sign is always placed to the driver's right at an intersection. Conceptual compatibility refers to the degree to which symbols and words presented on a sign match driver expectations. For example, a stop sign is always octagonal in shape, so drivers associate the shape with the act of stopping. Physical representation refers to the degree to which the content of a sign represents reality. In this case, the sign needs to accurately inform a driver of a roadway circumstance (e.g., falling rocks). Familiarity refers to the extent of the driver's experience with a specific sign. Some drivers may encounter signs that are uncommon (e.g., minimum freeway speed limit) and may be confused as to the meaning. This lack of familiarity can be an issue, if the sign is designed to serve as a warning or in cases of driving in foreign countries. The last guideline is standardization, which refers to the level of consistency in the design of the signs. Shape, color, and pictorial elements should be consistent for each specific type of sign; otherwise, driver interpretation can be compromised if different designs are used for the same purpose. [PERSON] & [PERSON] [20] found that pairing pictorial information with text on road signage presentation improved interpretation accuracy, even when the sign was unfamiliar to the driver. While the presentation of roadway signage information through an in-vehicle display potentially allows for more creative designs, as well as greater flexibility in timing and duration of communication, such displays may still benefit from consideration of existing ergonomic principles for roadway signs due to driver prior adaptation. Beyond the formatting of signs, the physical location of the sign on the roadway is another important human factors consideration. Although many drivers have experience with different types of roadway signs, there are barriers to recognition due to the signing environment and sign configuration [21; 22]. For example, driver awareness of a road sign can be easily affected by weather (e.g., fog vs. clear), lighting conditions (e.g., night vs. day), vegetation (e.g., tree branches covering a sign), sign legibility (e.g., font size of a street name being too small to see), and language used in signs (e.g., foreign drivers face difficulty in understanding local signs). In addition, driver compliance with a road sign may be low, even if they comprehend the sign, as they may not associate the sign with a necessary action. For example, a driver may ignore the need to stop at a stop sign when there is no traffic at an intersection. In a comparison of studies on driver compliance with conventional stop signs between 1931 to 1999, traffic counts revealed a sharp decline in the percentage of drivers who made a full stop at stop signs from 47% in 1931 to 1% in 1996 [23] (p. 2775, Table XIV). Drivers in full violation of a stop sign increased from 42% in 1931 to 97% in 1996. With higher levels of vehicle automation, drivers may not need to perform some or all aspects of the driving task, thus their visual scanning and vigilance of the roadway may degrade, as compared to manual driving [24]. As a result, driver processing of signage on the road could be further limited or even abandoned.