The increasing urban sprawl, car ownership, dependency, and the mechanization of urban life have affected people’s tendency to walk 
. Low non-motorized share has resulted in various problems, including congestion, longer travel time, air, and noise pollution, overweight due to diminished physical activity, and staggering economic costs 
. According to the most recent data from the World Health Organization, about 4.2 million people died because of air pollution and the resulting disease. Moreover, more than 1.9 billion adults, 18 years and older, were overweight which over 650 million were obese in the world. Based on this report, 25.8% of people are obese, and 27,000 people died because of air pollution in Iran 
. This has gradually highlighted the necessity of encouraging people to choose active travel modes, such as cycling and walking. There are many reasons for preferring walking among people due to travel-related factors as well as mental, social and environmental health. Walking has many advantages over other transportation modes such as independence from motorized traffic congestion, lack of need for parking, lack of air and noise pollution, low/no monetary cost and improvement in mood and relieving stress 
. In this regard, local authorities also attempt to increase the share of active travel modes to favor physical activity, improve air quality, reduce the accident rate, lift spirit and mood, and lower inevitable fatalities 
Identifying factors affecting sustainable transportation modes is essential to increase walking and thus benefit from its potential advantages. This would lead to proper planning and policymaking to achieve the goals and perspectives in encouraging people towards walking 
. Among the critical factors in walking likelihood, most studies have acknowledged distance as a key element. Still, contradictory findings have been seen for different trip purposes, age groups, and environmental contexts 
. For example, Larrañaga et al. 
found that with an increase in trip distance, the probability of choosing walking in work, educational, and recreational trips reduced in Brazil. Hatamzadeh et al. 
investigated walking likelihood across genders in school trips to study the effect of different distance intervals (increasing by 0.25 miles) on walking likelihood in Rasht, Iran. They found that with an increase in trip distance, the probability of choosing walking reduced, and boys are more sensitive to walking distance than girls. In terms of first/last mile of trips, Paydar et al. concluded that the average preferred walking distance between origin and metro stations is 336 m in Shiraz, Iran 
. Tsunoda et al. 
explored the accepted walking and cycling thresholds of Japanese elderlies and found 1 and 2 km as the acceptable distance for walking and cycling, respectively. Besides, Piccioni et al. 
identified a range of 500 m (0.31 miles) as an acceptable walking distance in an urban environment, intended as the maximum average distance people are willing to travel to reach their destination for both mandatory and discretionary trips. Agrawal and Schimek 
investigated the effect of socio-economic characteristics and BE variables on the duration and length of walking trips in the USA. They found that the average distance of recreational walking trips is twice as large as that for work trips (1 mile vs. 0.5 miles).
Further, the lowest and highest recreational walking distance belonged to children and adults (30–64 years, 1.25 miles). Hatamzadeh et al. 
explored the probability of choosing walking for working and shopping trips across genders in Rasht, Iran. They found that, on working trips, the effect of trip distance on the walking likelihood of women was more than men, while on shopping trips, the relationship was vice versa. In addition to the trip distance, many contradictory findings have been reported in the literature about the impact of travelers’ age on walking distance and likelihood. For example, Pucher and Dijkstra 
found that as people get older, the number of walking trips would reduce in the Netherlands and Germany. Moreover, elderlies (aged above 65 years old) walk 25% less than the average number of mandatory walking trips while they walk 39% more than this amount for recreational and exercise trips. Meanwhile, Teshome 
reported a direct relationship between the probability of walking and age in work trips in Ethiopia, while Rodriguez and Joo 
reported an inverse relationship in the USA. Larrañaga et al. 
found that as an individual gets older, the probability of choosing walking decreases on work, educational, and recreational trips in Porto Alegre, Brazil.
According to the above-mentioned research, it can be found that most studies used distance as a continuous variable and did not categorize it into smaller intervals for a more accurate analysis. In addition, the effect of trip distance on walking likelihood in different trip purposes has been studied only for specific groups such as men and women, elderlies or students, limiting the applicability of the proposed model. Further, there are also quite contradictory results regarding travelers’ age. Given the different nature of such kinds of trips, in terms of spatial and temporal characteristics, walking behaviors and thus model specifications seem likely to be completely different. Mandatory trips (i.e., work and educational activities) occur at specific places and times.
In contrast, discretionary trips (i.e., shopping and leisure activities) are more flexible and could be even avoided or shifted to off-peak hours in the neighborhood of travelers’ residing location by implementing appropriate policies.