1. Introduction
As health problems such as overweight and obesity become more serious, various studies and policies are being conducted and implemented in many countries to promote physical activity in urban environments [
1,
2]. Many studies showed that the structure of urban environments affects walking [
3,
4,
5], physical activity [
5,
6,
7,
8,
9,
10,
11,
12], and obesity [
9,
10,
13,
14]. Improvements in the built environment can function to encourage people to walk and to be physically active in their daily lives, and could thus have a positive effect on residents’ health condition [
15,
16,
17]. Korea is not free from this health issue, the Community Health Survey of Korea revealed that the rate of walking has decreased from 50.6% (’08) to 39.7% (’17), and the rate of obesity has increased from 21.6% (’08) to 28.6% (’17) over the past decade [
18]. This increase in obesity and sedentary lifestyle patterns has emerged as a social problem in Korea, which has led to studies on pedestrian-friendly urban environments [
19,
20,
21].
According to a sample survey of daily traffic logs using GPS, the total daily time spent in traffic by Seoul citizens is 91.0 min, walking traffic accounts for 42.5 min of this time (47.0%) [
22]. This indicates that walking is an important part of Seoul citizens’ daily lives. Thus, creating a pedestrian-friendly environment has become a priority. The city of Seoul recently announced a mid- to long-term plan for promoting walking over the next five years. This plan was developed on the principle of creating an urban environment that prioritizes walkers throughout Seoul [
23].
According to data from the 2017 Community Health Survey, the obesity rate in Seoul was the lowest of 17 metropolitan cities and provinces at 25.5%, while the rate of walking was the highest at 61.5% [
18]. This indicates that Seoul citizens’ health behaviors are relatively good. Thus, it was determined that measuring the walkability of Seoul’s environment and utilizing these data in various research and policies would be useful. By measuring walkability to identify the spatial distribution characteristics of the walkability level, the city government will be equipped to establish urban planning and transportation policies to enhance citizens’ walking. For example, it is expected that various urban planning policies (e.g., the improvement of pavements on pedestrian roads, the installation of pedestrian-only streets, and improvements in the traffic signal system for pedestrians) could be developed to improve neighborhood environment of the area by identifying the vulnerable area of walking.
Among the studies on building pedestrian-friendly environments, some have attempted to develop walkability indices that measure pedestrian urban environments [
24,
25,
26,
27,
28]. However, only a few studies of walkability have been conducted in Korea [
28]. For example, the walk score, which is widely used as a walkability index in various fields in the US, such as real estate, urban planning, transportation engineering, and public health, provides data on cities in the United States, Canada, Australia, and New Zealand only. Walk score data are not available for Asian and European cities. Research on the development of a walkability index has only recently emerged in Korea.
One purpose of this study is to measure walkability levels in Seoul, Korea. This will help develop various policies within the fields of urban planning, urban design, and transportation to promote walking. It is important to select the appropriate index to measure walkability levels. Many previous studies have used several indices to measure walkability at the neighborhood, community, and city levels. Thus far, approximately 80 or more walkability indices have been used [
29], and it is very important to choose an appropriate index to measure the walkability level of a specific area. Many studies have attempted to determine how urban forms affect walking, and these variables have been grouped into five categories, which are collectively referred to as the five Ds (density, diversity, design, destination accessibility, and distance to transit) [
30].
One study suggested eight walkability indices that correlate with active transport: Walkability index (WI), walk score (WS), walk opportunity index (WOI), pedshed (Ps), extended walkability index (EWI), movability index (MI), neighborhood destination accessibility index (NDAI), and pedestrian index of the environment (PIE) [
31]. These eight indices have different components, but some are similar. It is notably difficult to choose which of these is the most effective index to use. In recent walkability studies, WI, WS, Ps, and MI have been used often [
5,
26,
31,
32,
33]. These four indices also relate to active transport behavior as well as the five Ds.
The WI was developed by Frank et al. [
34] and is the most popular measure in urban planning and active living literature [
5,
35]. The WS was developed by a commercial company in Seattle, US [
36] and is one of the most popular indices. It is based on a measure of access to nine types of destinations (e.g., grocery, coffee shop, restaurant, etc.). Pedshed is a commonly used index to represent accessibility and measures the area accessible through the street network as a percentage of the area [
26,
31]. The MI is developed on the basis of the existing WI but is intended to include movability in the WI. It includes accessibility to recreational facilities such as playgrounds and sports facilities [
32]. Are these indices reliable? To answer this question, we must calculate the walkability of Seoul using popular indices including WI, WS, Ps, and MI and confirm the reliability of the indices. While a significant amount of research has been conducted on the development of walkability indices, little research has been conducted on their measurement reliability, which is what this study attempts to address.
Reliability is determined by consistency, stability, dependability, reproducibility, predictability, and lack of distortion. High reliability means that the same or comparable measuring instrument can produce the same or similar results if the same set of objects is measured repeatedly [
37]. On applying the concept of high reliability in this study, regardless of the index used to measure the level of walkability of Seoul, the results should be the same or similar.
Reliability assessment is a general practice of conducting analyses such as test-retest, intra-rater, and interrater reliability on survey data. However, there are some studies to measure the inter-method reliability [
38,
39,
40]. This research is also an inter-method reliability study of the walkability level. It examines the reliability among the indices that measure the level of walkability in Seoul and considers the possibility of applying them to measure the walkability in other cities in Korea. If there is no reliability between the indices, research methods can be examined on the direction of index development to suit the conditions in Korea.
As mentioned earlier, not only has the walking rate of the average Seoul citizen increased steadily over the past decade, but the city government has also continued to implement policy efforts to create a pedestrian-friendly urban environment. Thus, reliable measurement methods for examining the walkability of Seoul’s built environment are necessary. The purpose of this study is to calculate the level of walkability in Seoul, Korea, using WI, WS, Ps, and MI and to further check measurement reliability between those indices.
4. Discussion
Before this study was conducted, few studies had developed a walkability index in Korea [
28]. Furthermore, no studies had been conducted on the measurement reliability between walkability indices. This study used four types of indices, WI, WS, Ps, and MI, to measure the walkability of the environment and checked the reliability of the measure between these indices in Seoul, Korea. The study area was the total area of Seoul, excluding rivers and greenbelts. Using 100 × 100 m grids as units of analysis, walkability values were obtained for 44,000 total points.
The findings of this study are as follows. First, quintile maps using the four indices showed slightly different shapes locally but a similar pattern across Seoul in general. Since the factors evaluated in each index are different, differences in the walkability levels were observed depending on which index was used. For example, the MI measures elements such as street connectivity, destination density, and level of urbanization, whereas Ps measures pedestrian catchment. Therefore, differences between the MI and Ps scores were expected. Nevertheless, it is noteworthy that quintile maps of the four indices exhibited similar patterns. Second, the hotspot analyses showed that Moran’s I value ranges from 0.530 (pedshed) to 0.815 (movability index) at a 0.1 significance level, indicating that all four indices exhibited significantly high spatial autocorrelation. Since the distinction between hotspots and coldspots was apparent by region, different urban planning and policy approaches may be applied to improve walkability levels in each region. Specifically, it would be suitable to suggest various policies for coldspot areas with poor walkability. Third, the results of the analyses using Pearson’s R, the Brand–Altman plot, and the ICC reveal that the measurement reliability among the four indices was significantly high. The Pearson’s R values were in the range of 0.308 to 0.645, and the range of inside LOA of the Brand–Altman plots was 94.5% to 95.5%. Furthermore, the ICC value among the four indices was 0.544 (moderately reliable) at the 0.1 significance level. This indicates that the four indices have statistically significant high measurement reliability. Researchers can begin to utilize any of these four indices for measuring the walkability of other cities in Korea. Additionally, future studies need not hesitate to choose either of these methods and among the indices used in this study, an index that is easy to collect data and low cost of measurement will be available.
This study brings to light three major points of significance. First, this study is meaningful in that we empirically verified measurement reliability between walkability indices in Seoul, where there has been little walkability research. Furthermore, there have been few studies that have checked the reliability between walkability indices. Second, while studies of measurement reliability have generally focused on looking at the overall level of measurement reliability, this study divided the study area into disaggregated levels for checking measurement reliability. Specifically, when comparing ICC values, this study carried out its analysis by using administrative units (gu). Third, to check measurement reliability, this study used several methods including Pearson’s R, Brand–Altman plot with LOA, and ICC. Thus, the reliability of the results has been greatly enhanced using the triangulated methodology application rather than a single method.
Although this study is meaningful in checking the reliability of walkability research methods, some limitations remain. This study used four indices of walkability to verify the reliability among them and found that they had statistically significant high measurement reliability. However, depending on which index was used and which district was analyzed, the results of the study could be different. In particular, if we take a closer look at some parts of the city of Seoul, we will definitely find some places that exhibit lower levels of reliability. To address this problem, a validation check on walkability measurement should be performed. Several studies have examined the validation of walkability by analyzing its correlation with health-related variables such as walking [
1,
35] and physical activity [
27]. In future studies, it may be possible to check the validation of walkability with pedestrian satisfaction and active transport.
This study provides information on the feasibility of data preparation and appropriateness of analysis methodology, not only in Seoul but in other cities in Korea as well. Based on these results, walkability levels in other cities can be measured with greater surety. This enables urban planners and policymakers to provide ideas on the desired direction of walkability index development while considering spatial characteristics. We look forward to seeing a variety of urban planning policies that promote walkability.