# Evaluation of Adjustment Effects of Highway Guide Signs Based on the TOPSIS Method
## 4 Construction of Evaluation Index System
### Evaluation Metric Determination
#### 4.3.2 Readability Indicators  
Based on the factors affecting the readability of guide signs, the following evaluation indicators are proposed. 1. Compliance rate of layout standards (D4)  
This indicator assesses whether guide signs meet standards in design elements like color, shape, font, and directional arrows. For highways and urban expressways, guide signs should have a green background with white symbols, a white border, and green edging, with a square shape. Fonts should primarily be in Chinese, with additional languages or English if needed; English names must follow pinyin rules, capitalizing only the first letter. Up to six types of directional arrows are permitted, including right, diagonal right, straight, and diagonal left. This metric is the proportion of compliant guide signs to total signs. \[D_{4}=1-g_{21}/G \tag{14}\]  
\(D_{4}\) is the compliance rate of layout standards, \(g_{21}\) is the number of signs that do not meet standards, and \(G\) is the total number of guide signs. 2. Visual comfort of layout (D5)  
The comfort experienced by highway users depends on both the design of the signs and environmental factors. Poor design may increase driver fatigue and elevate the risk of traffic accidents. To assess visual comfort, an attitude scale is applied, with five levels of satisfaction: very satisfied (5 points), satisfied (4 points), neutral (3 points), dissatisfied (2 points), very dissatisfied (1 point). Score = Total score from all questionnaires/(5* number of questionnaires). 3. Non-overload rate of layout information (D6)  
When the amount of information on a guide sign exceeds recommended limits, drivers may struggle to recognize and process key details in time, potentially compromising safety. According to the standard, the total number of destination entries on a single sign should not exceed six per direction. This indicator is defined as the ratio of signs with non-overloaded information to the total number \(G\) of guide signs. \[D_{6}=1-g_{22}/G \tag{15}\]  
\(D_{6}\) represents the rate of non-overloaded signage information, while \(g_{22}\) denotes the number of overloaded signs. 4. Unobstructed signage rate (D7)  
Guide signs may be blocked by trees, vegetation, or other structures, impairing visibility and reducing their effectiveness. This indicator is defined as the ratio of guide signs that are not blocked by obstacles to the total number \(G\) of guide signs. \[D_{7}=1-g_{23}/G \tag{16}\]  
\(D_{7}\) represents the rate of unobstructed signs, while \(g_{23}\) denotes the number of obstructed signs in the directional signage. 5. Intact reflective film rate (D8)  
Reflective films enhance the visibility of guide signs at night, contributing to driver safety. However, signs with faded, cracked, or peeling reflective film reduce visibility and hinder the communication of critical information. This indicator is defined as the ratio of guide signs with undamaged reflective film to the total number \(G\) of guide signs. \[D_{8}=1-g_{24}/G \tag{17}\]  
\(D_{8}\) represents the completeness rate of reflective film, while \(g_{24}\) denotes the number of directional signs with incomplete reflective film. Maintenance rate for clean signage (D\({}_{9}\))  
Guide signs exposed to outdoor elements are prone to dirt accumulation, which reduces their visibility and effectiveness. Regular maintenance is essential to keep signs legible. This indicator is defined as the ratio of signs free from dirt and damage to the total number \(G\) of guide signs. \[D_{9}=1-g_{25}/G \tag{18}\]  
\(D_{9}\) represents the maintenance rate of signs with dirt, while \(g_{25}\) denotes the number of dirty signs among directional signs. Alignment accuracy rate (D\({}_{10}\))  
Guide signs may bend or tilt due to wind loads, especially in coastal areas where severe weather is frequent. This indicator is defined as the ratio of guide signs with correct alignment to the total number \(G\) of guide signs.