Performance Comparison of Three Freeway Guide Sign Alphabets

Abstract

Modern fully retroreflective legends can create a blooming effect that reduces legibility. In this research project three alphabets were evaluated to determine whether the legibility of a white high-intensity legend on a green high-intensity background could be improved by reducing the blooming effect. The three alphabets were: Series E(Modified), Clearview, and British Transport Medium. Overhead and ground-mounted sign positions were evaluated in both daytime and nighttime conditions. There was no sign illumination for the nighttime conditions other than the vehicle headlights. Both legibility (unknown word) and recognition (known word) distances were measured. A total of 54 subjects participated in both daytime and nighttime trials. There was significant variability in the results of the various experimental conditions. In general, the results indicated that Clearview was slightly more legible than Series E(Modified) in the overhead position in both daytime and nighttime conditions. The extent of improvement over Series E(Modified) was generally in the range 2 to 8 percent. The greatest improvement was achieved for worst-case drivers. Clearview ground-mounted signs were less legible than Series E(Modified) in daytime conditions. In nighttime conditions, the ground-mounted Clearview signs did not demonstrate a consistently better performance than Series E(Modified). A greater degree of improvement was realized in the recognition of Clearview in the overhead position for both day and night conditions. British Transport Medium was generally less legible than Series E(Modified).

Empirical Assessment of the Legibility of the Highway Gothic and Clearview Signage Fonts

“…However, the notice of discontinuation overlooks most research on Clearview. Even though some studies have found Clearview not to hold a legibility advantage (13)(14)(15), many others have reported significant evidence that Clearview is more legible (16)(17)(18)(19)(20)(21)(22)(23). Even Miles et al, who dismiss Clearview in the summary of their evaluation, found results that could be described as mixed at worst: Clearview improved legibility distances for older drivers during the day but not at night (15).…”

“…The real-world validity of such assessments has obvious advantages, but many limitations and uncontrolled variables apparent in this general design can complicate interpretation of results. Several studies distinguish day and night driving (14)(15)(16)(17)21), but only one reports an attempt to account for whether the day was sunny or overcast (22), which can reduce the amount of available illumination by as much as half. Results also may be affected by the particularities of the test track and surrounding area, the type and size of vehicle driven, whether the research participant is driving or reading signs as a passenger, and how fast the vehicle is traveling-which ranges from 8 km/h (5 mph) to 56 km/h (35 mph) in these studies (14,15).…”

“…Results also may be affected by the particularities of the test track and surrounding area, the type and size of vehicle driven, whether the research participant is driving or reading signs as a passenger, and how fast the vehicle is traveling-which ranges from 8 km/h (5 mph) to 56 km/h (35 mph) in these studies (14,15). All but one of the aforementioned studies relies on participants to report responses verbally, which introduces unavoidable and unpredictable delays between stages, including the driver's accurate perception of the sign, initiation of a verbal response, the experimenter's recognition of the response, and recording of the legibility distance (17). These delays introduce an uncontrolled source of noise in the data, especially with the vehicle traveling at a high speed relative to human-scale action.…”

Maximizing Legibility of Unlit Freeway Guide Signs with Clearview Font and Combinations of Retroreflective Sheeting Materials

“…To date, three research studies have reported on the visibility impacts of using guide signs made with the Clearview font instead of the currently specified Series E (Modified) font (14)(15)(16). The results of the studies show an evolution in the testing techniques and results; the most recent study, completed with full-scale signs made entirely of microprismatic retroreflective sheeting, showed significantly increased legibility distances with guide signs made with the Clearview font as compared to those made with the Series E (Modified) font (16).…”

The Effects of Ambient Illumination, Color Combination, Sign Height, and Observation Angle on the Legibility of Wayfinding Signs in Metro Stations

“…Legibility is a commonly used ergonomic criterion for display evaluation [13][14][15][16][17][18]. Recognition and legibility distances are indicative of a sign's visual performance [19], and they are used as the dependent variable in experiments of traffic signs in many articles [20,21]. Recent works on text legibility are mostly focused on screens at a short distance with subject rating scores or reading time.…”