Planning of Transportation Infrastructure Networks for Sustainable Development with Case Studies in Chabahar

Abstract

This article addresses the problem of increasing transport services that intercontinental corridors demand from the urban infrastructure networks along their routes. Yet, attention has not been paid to the coordination between the transportation potentials of a city infrastructure network located on the path of an intercontinental corridor and the sustainable application of the corridor itself. This article discusses solving this problem by increasing the transportation capacities of the cities on the path of the corridor. With field studies in Chabahar, we observe the situation of its transportation infrastructure network to discover shortcomings and suggest required changes. This paper recommends the necessary changes and improvements in the urban transportation system of Chabahar to have a sustainable intercontinental corridor and an effective urban infrastructure network simultaneously. The research methods used include observation of traffic flow and behavior in travel origins, destinations, and paths in Chabahar. Then, this study builds a mathematical model with a graph technique to calculate the traffic capacities on the nodes and streets and determine places that require changes. Analyses show that 13,420 cars enter just the center of Chabahar city due to the increasing pressure of the Chabahar–Milak corridor. This paper recommends a multi-modal transportation system with an urban public transport network. It also suggests physical and geometric corrections in sight distances and longitudinal curves of streets, sidewalks, and squares. We find urban transportation failures in the city and present a comprehensive transportation plan for its improvement. This model is applicable in all cities on the route of corridors and assists their sustainable function and urban transport system simultaneously.

1. Introduction

Transportation systems are constantly evolving in their infrastructure, types of machinery, applied technologies, standards, and regulations, as well as supplying services. Recent information technologies have still accelerated changes in transportation systems [1]. The expansion of regional and international trade relationships is one factor that has led to the development and advancement of transportation infrastructure networks. This paper studies the optimization of traffic flows by improving transportation infrastructure networks of cities along international corridors. The subject as a strategic policy has been noticed to coordinate the urban transportation system with an increase in transportation needs. Scientists optimized transport between ports and regions considering the new demands [2]. Scholars explored the improving quality of logistics services of dry ports within Eurasian transport corridors. This study has been newly conducted in the Khorgos Gateway in Kazakhstan and recommends ways to reform urban transportation infrastructure in the context of an international corridor [3]. Other scholars have also proposed procedures to reform urban streets to service new demands [4]. The expansion of businesses in Poland between 2004 and 2014 encouraged investment in the construction of motorways and roads to improve access to markets and increase job opportunities [5]. Planning for international/continental transportation corridors such as the Silk Road and Transport Corridor Europe–Caucasus–Asia (TRACECA) are currently being discussed [6]. In these plans, attention is paid to the intercontinental corridors, not the potential of cargo and passenger transportation of a city that the corridors pass through. We assume that if the urban transportation system on the route of a continental corridor does not respond to the new needs, the corridor project will not be successful either. Therefore, this innovative paper recommends necessary strategic reforms in the urban transportation system of Chabahar to coordinate with the new needs of international corridors. With a common hypothesis to us, Qin and colleagues analyzed the transport infrastructure networks of cities on the route of the new western land-sea corridor in China [7].

Two subjects are considered in this paper: one is the wish to connect urban transportation to international/continental corridors and the other is urban transportation planning for new standards, land-use policies, and per capita. Transportation infrastructure networks shall increase per capita land use in streets, sidewalks, intersections, plazas, stations, terminals, and transport offices upon the application of professional engineering studies. Several cities have already started to provide more spaces on sidewalks, bike lanes, streets, stations, and vehicles to lighten the pressure of traffic and take measures to protect passengers in travel [8]. The international transport forum with 62 member countries also encouraged cycling, walking, and providing adequate space for social distancing to combat the pandemic [9]. For socio-economic development and rapid movement of commercial goods, and the health and comfort of passengers, urban transportation networks require planning and design with new standards and legislation. Scholars use transportation planning and regulation to improve urban mobility concerning the interests of travelers, markets, the environment, and society [10]. Successful ports such as New York, Dubai, Qatar, Hong Kong, and Singapore took advantage of the transportation systems to develop international trade and to improve the indicators of economic prosperity and quality of life [11]. A rethink of the planning and design of the Chabahar urban transportation system is also necessary, considering the new need for improvements and the opinions of scholars. The need for upgrading Chabahar’s transportation capacity arises from the connection between the Chabahar port and Nimrouz (in Afghanistan) through a corridor, which requires better urban transportation networks [12]. In terms of international cargo transport, Chabahar port has become a primary provider of raw materials and an importer of consumer goods. The Chabahar transportation system connects land and air infrastructure to maritime lines by decreasing travel times and increasing reliability [13].

The Chabahar port has been a trade center since early [13]. Its export values to Turkmenistan, Uzbekistan, and Tajikistan have increased by 17%, 49%, and 52%, respectively, in the recent decade [14]. Recently, the importance of strengthening intra- and inter-regional transportation connectivity has been noticed in connecting Chabahar to global commercial networks [15]. However, the increasing commercial travel has placed more load on the urban transportation system of Chabahar, which is greater than its capacity. The increase required the simultaneous development of the Chabahar urban transportation system connection to the intercontinental corridor, which passes from Singapore, Europe, and China [16]. Simultaneously, the planning and design of sustainable urban transportation shall be aligned with the international policies and standards of transportation [17]. The question is: what reforms should be made to the urban transportation system so that the city can adapt to its growing transportation needs? A review of research conducted on the urban transportation system of Chabahar shows that this question has not yet been explored. A gap exists in research on recognizing the shortcomings, weaknesses, and needs of the Chabahar transportation system, which this article addresses for the first time. This article aims to increase the transport services that intercontinental corridors demand from the weak urban infrastructure networks along their routes. The case studies in this paper aim at revisions in the urban transportation infrastructure network of Chabahar to improve its services in harmony with the intercontinental corridors. Our studies also propose to improve the environment sustainably by reducing emissions and noise pollution caused by the urban transportation system, similar to what scholars have recommended for reducing emissions in the road transport sector [18,19,20]. With field studies, observation, and experiences, this paper determines the required type of changes in the urban transportation infrastructure network of Chabahar. The aim is to plan and design an urban transportation infrastructure network with the new requirements of Chabahar and its particular situation. The outcomes of this paper will assist engineers and planners everywhere in urban transportation planning and design, such as physical and geometrical corrections of paths, nodes, and spaces.

2. Methods and Materials

2.1. Methods

Our applied research hypothesizes that the sustainable and effective operation of international corridors is possible by modernizing and improving the transportation infrastructure of the cities along its route. The research method is based on the current situation of the transport network of Chabahar city while exploring the relevant literature. The result is an understanding of the corrective design of the urban transportation network based on its future needs. Field studies have been conducted on the knowledge of the origins and destinations of travels, travel behavior, and sizes and shapes of nodes, lines, and stations. At the same time, the ideas of the interviewed riders concerning the quality of urban transportation infrastructure have been explored. The environmental effects of the transportation network and the lack of public transportation networks have been noticed, too. By using observations, field experiences, and mathematical models with graph rules, we proposed corrective designs for future needs. The innovation in this research is in planning and designing the correction for the urban transportation network according to the increasing needs due to the city’s connection to the Milk-Chabahar corridor. As far as we reviewed the literature related to this issue, this research offers new ideas for providing sustainable and efficient urban and international transportation systems. Based on this, we have determined the locations and types of improvements or reconstruction needed within the city’s transportation network. The literature review makes it clear that transportation networks are evolving. One evolution factor is a connection to international corridors and thus the need for the globalization of trade and transportation services. Nevertheless, there is still not enough research on the systematic relationship between the strategic design of corridors and transportation through the cities on the route.

2.2. Case Studies

A case study strategy has been conducted in Chabahar to plan reforms in the transportation infrastructure system and increase international transportation. Figure 1, below, exhibits Chabahar’s location.

In Figure 1, a suitable place for Chabahar to connect to international transportation corridors on the Sea of Oman and the Indian Ocean is visible. Figure 2 shows a land use map of the Chabahar port. In 2012–2015, Iran’s share of cargo transportation increased from 8.5 percent to 12 percent volume due to the Chabahar–Milak corridor, which is a section of the major Euro-Asia corridor.

Figure 2 shows Chabahar with its narrow and organic streets and avenues, which cannot host passengers and cargo due to its initial transportation system. The figure also shows the potential capacities of Chabahar to develop its maritime, air, land, and rail transportation infrastructure networks. Chabahar has approx. 350,000 inhabitants (Statistical Center of Iran). Our analyses show the need for a comprehensive transportation system.

2.3. Materials and Data

Considering the need for more traffic due to the role of Chabahar Port in the Chabahar–Milak international corridor, we conducted integrated traffic studies for the most important travel destinations. Eight people observed and registered travel behavior from eight origins in detail. On three different days, 30 March 2020, 3 July 2021, and 16 January 2021, we counted passing cars in the city from 8:00 am to 8:00 pm. The numbers for the three days were different because we had chosen the days in different seasons, holidays, and working days. The supplied travel statistics that illustrate the present traffic in capacities, delays, and jams. We asked the drivers of cars entering and exiting: where did they come from and go? We also questioned their opinion about the travel route and necessary reforms. In this way, we gathered information related to travel-generating and absorbing centers. Information concerning parking, public transportation, and pedestrian traffic has also been collected. In the second step, we applied the rules of graph theory to network analysis and modeling. At this stage, we have provided effective solutions to improve the state of the urban transportation infrastructure network to increase traffic efficiency. In this way, we determined the locations for changes in the geometric and skeletal design of streets, sidewalks, squares, intersections, longitudinal and transverse slopes, and viewing angles. The number of trips in the mentioned time is in

Table 1. The total number of various types of travels with their origins and destinations.

Origin	Destination	Number	Subtotal	Total
Chabahar	Free zone	2160	5187
	Workplace	282
	Komb	98
	Near towns	1535
	Rock beach	70
	Gulf beach	51
	Lipar hotel	991
Free zone	Chabahar	1873	2763
	Workplace	410
	Gulf beach	78
	Rock beach	115
	Lipar hotel	263
	Komb	24
Workplace	Chabahar	292	1116
	Komb	312
	Free zone	512
Komb	Chabahar	144	480
	Free zone	31
	Workplace	281
	Near towns	24
Near towns	Chabahar	1440	1518
	Rock beach	46
	Komb	32
Rock beach	Chabahar	72	328
	Free zone	142
	Near towns	52
	Gulf beach	62
Gulf beach	Chabahar	48	204
	Free zone	75
	Rock beach	81
Lipar hotel	Chabahar	1512	1824	13,420
	Free zone	312

.

Table 1 shows the number of travels in the origins and destinations from 8 a.m. to 8 p.m. in Chabahar. The supplied statistics about travel behaviors could assist us in assessing the traffic capacity of the urban transportation lines and nodes for re-planning and design. With the re-planning of the urban transportation networks, we shall increase the capacity of transportation for future needs. Figure 3 shows the origins and destinations that produce the majority of travel in Chabahar city with data from Table 1.

The chart above shows that 38.65% of travel is Chabahar-based. This figure is more than other types of travel. For instance, 8.3% are workplace-based travel. Lipar hotel-based travel and near-town-based travel are 13.6% and 11.3%. Free zone-based travel includes 20.58% of the total travel. They encompass 57.3% of total travel, which shows increasing travel in Chabahar correlated with the international corridors. From the sustainability view, an intercontinental way must work optimally. If a node, such as Chabahar, does not work efficiently, the corridor system will also suffer a crisis, and its function will be unstable. The cognition of travel behavior and traffic in Chabahar urban transportation infrastructure assists us in planning required reforms for the strategic and sustainable corridor. Our professional field observations show that streets and passages have an organic essence. This network of streets and alleys was created due to the pressure of daily needs in recent decades and not according to maps. Of approximately 2300 hectares of urban land, only about 380 hectares are for transportation lines, urban facilities, and equipment. However, the land allocated to streets is much less than 16.5% of the total land area in Chabahar. Chabahar city requires a new physical structure and infrastructure network to adapt to the international/intercontinental corridor systems. The urban transportation network system of Chabahar shall accord to particular economic and geopolitical characteristics. People constructed the narrow streets for the needs of the earlier small populations without cars in spontaneous development. United Nations Habitat requires at least 30% of urban land for a street network to build a non-dormitory, efficient, and vibrant city. Chabahar needs at least 18 km of streets per square kilometer of its area [23], particularly considering the impacts of the Afghanistan–Milak–Chabahar corridor [24,25]. Chabahar has not allocated enough land for the streets, sidewalks, terminals, and stops. The streets need changes at sight distance, including stopping sight distance and passing sight distance. The streets need geometric correction in level and non-level crossings and pedestrian abutments at intersections. Our professional field observation shows that the slopes of streets, sidewalks, and cross-sections in vertical and horizontal curves are incorrect and need earthworks in street flooring. Chabahar does not care about the public transportation system, and most of the city’s streets are without bus lines. Its two bus lines have worn-out buses and no regular itinerary.

3. Traffic Planning for New Needs

3.1. Modeling

Planning for the traffic flow in Chabahar regarding new requirements caused by the international corridors should supply data concerning the following issues:

• The number of travelers from and to Chabahar;
• The number of cars entering the city and leaving it;
• Probability of choosing a travel mode in a city;
• The best route between an origin and a destination;
• Travel costs of passengers or transport costs of cargo on every route.

The measurement of traffic capacity in transportation networks was discussed in the lectures of prominent professors. The lectures were published for the first time in the book Networks in Action, which used the graph in the analysis of transportation networks [26]. The use of the graph theory method for the optimization of shipments between ports and consignors/consignees is important from a theoretical and practical point of view and has aroused great interest among transport researchers and logistics companies [2]. Using the gravity model, the normalization technique, the adjusting factor, and graph laws, the number of trips or the weight of cargo will be calculable. The gravity model had been used earlier by scientists to model and plan urban transportation [27]. Here, let us begin with the following equation.

$${T^{\prime }}_j=T_j\times \frac{{\sum }_{i=1}^j{T}_i}{{\sum }_{j=1}^j{T}_j}\ge T_j\times \frac{237}{212}=T_j\times 1.12$$

(1)

In Equation (1), $T_{ij}$ is the number of travels from and to Chabahar, which in our case studies is 13,420 total travels. $T_i$ is the number of travels from the Chabahar origin equal to 5187 travels and $T_j$ the number of travels to Chabahar, 5381. Using data from the case studies with gravity, the Equation (2) is to be as follows:

$$T_{ij}=T_i\times \frac{T_j\times f(C_{ij})\times K_{ij}}{{\displaystyle {\sum }_{j=1}^n{T}_j\times f(C_{ij})\times K_{ij}}}$$

(2)

In Equation (2), $f(C_{ij})$ represents travel costs and $K_{ij}$ is the degree function. The data gathered by the case study shall be set in Equation (2) to normalize the number of trips to the destinations. Modeling for the Chabahar traffic flow requires forecasting travel behavior. By setting the origin-destination matrix, the routes that the passenger or cargo choose has been analyzed. Considering that economic sanctions affected ordinary people, the probability of choosing a travel mode in Chabahar city has been calculated using the following classical equation:

$$L={\displaystyle \prod _{n=1}^{N}f(Y_n}|X_n,\theta )$$

(3)

Equation (3), L is the maximum probability of a mode, X_n is the sample population that has been considered for n cars $\left\{1, 2, 3, \dots ,n-1, n\right\}$, and $\theta$ are parameters.

The next step of traffic planning is routing, to determine the best route between an origin and a destination, considering the price, time, and traffic capacity. Therefore, it is necessary to know the number of cars on each line or street. On a line (street) that connects two nodes, the number of travels shall be considered, which is equal to the number of cars entering and leaving the route. When the number of incoming trips is greater than the number of those outgoing, there will be a traffic delay. This observation recognizes that the total time a car spends entering a street can be minimized to prevent traffic jams. Following, a graph concerning the traffic of Chabahar has been drawn with its statistics. It uses the laws of the classic theory of graphs [28,29,30,31] with the data gathered in the field observation presented in Table 1. Figure 4 shows the network of streets that connect the free zone (F), workplace (W), Komb (K), near towns (N), Rock beach (R), Gulf beach (G), and Lipar hotel (L) to the center of Chabahar (H).

Figure 4 shows the capacity of traffic flow from one station to another. The red numbers show the cars entering Chabahar and the blacks show the cars leaving it. The green colored numbers are cars exiting other nodes. The numbers were calculated with experimental statistics along each line (street) in 12 h from 8 a.m.—8 p.m. The problem now is to determine the maximum capacity of the traffic flow on every route. To solve traffic flow and routing in Chabahar, we use the above graph and the technique of cut. The street network of Chabahar in the graph is V.

$$V=\left\{K, N, H, R, G, L, W, F\right\}$$

(4)

Imagine that $\overline{P}$ and $P$ are two subsets of V that have been separated by a curved line (cut) as follows:

$$P\cup \overline{P}=V$$

(5)

Chabahar city center H with K, N, R, and G are in $P$ and destination stations F, W, and L are in $\overline{P}$. Here, $(P,\overline{P})$ called a cut. This cut divides the graph of nodes in the network into two parts. To solve the problem of determining capacity and routing, 8 urban centers or nodes have been considered as follows:

$$P=\left\{K, N, H, R, G\right\} and \overline{P}=\left\{L, W, F\right\}$$

(6)

For every side of the graph, a positive real number exists that indicates the capacity of the traffic flow or the number of cars passing through it. For example, C (H, W) determines the capacity of the route from the origin of Chabahar (H) to the destination of workplace (W).

$$f\left(H, W\right)\le C\left(H, W\right) , where \left(H, W\right)\in V$$

(7)

$${{\displaystyle \sum }}_{H \in In \left(W\right)}f\left(H, W\right)-{{\displaystyle \sum }}_{H \in Out \left(W\right)}f\left(W, H\right)=\{\begin{array}{c}V for W=H\\ 0 for W\ne H\\ -V for W=H\end{array}$$

(8)

In (8), in is the number of cars coming into the city of Chabahar in our observed time (212 cars), while out is the number of cars leaving the city (237 cars). Now, we write for the capacity (number) of cars leaving Chabahar downtown (H) from the two parts of the cut $P$ and $\overline{P}$ as follows:

$$C\left(P+\overline{P}\right)=C\left(F, H\right)+C\left(l, H\right)+C\left(W, H\right)+C\left(K, H\right)+C\left(N, H\right)+C\left(R, H\right)+C\left(G, H\right)$$

(9)

To show this relationship numerically, we used the cutting of the Chabahar street network with the traffic capacity and the number of passing cars from Chabahar as follows:

$$C\left(P+\overline{P}\right)=1873+1512+292+144+1440+72+48=5381$$

(10)

Similarly, we calculate the travels coming into Chabahar with numbers denoted on the lines. With this model, we found the number of cars that travel on every route (street). With this cognition, we determine the capacity for traffic caused by the intercontinental corridor. The model’s calculation makes it possible to plan and design the transportation network under the current and future needs of Chabahar. The purpose of our mathematical planning model is to avoid queuing, minimize the consumption of time and money, and ensure a smooth flow of traffic. This model assists in determining traffic jam points to allocate more land and space with the reform plans.

3.2. Planning and Design to Improve Urban Transportation Infrastructure

We observed and analyzed the transportation infrastructure network of Chabahar city and recognized problems and priorities concerning the opinions of officials, car riders, and local people. Our studies showed the following shortages in the urban transportation system for collaboration with the international corridors:

• The transportation network system of Chabahar city is rudimentary and cannot take on the duties of an international city;
• The transportation system cannot use all its land, air, rail, and maritime potential because it lacks the necessary infrastructure;
• The transportation network needs re-planning based on new needs and the latest regional, international, climatic, demographic, cultural, and economic changes;
• The existing transportation system needs a quantitative and qualitative development of public transportation;
• The transportation network system needs investment to supply necessary services to manage traffic congestion in cities caused by the international corridors [31];
• The transportation system should coordinate with modern global transportation network systems by making its activities transparent and attracting public participation [32,33].

Traffic planning in the Chabahar transportation infrastructure network is to increase its traffic capacity, supply services for passenger and cargo transportation, and use all possible transportation modes. The mathematical model, expressed in equations 1–10 with the graph technique, revealed that the number of cars on the lines and nodes should be increased. The increase will be possible through new designs in sizes of streets, plazas, intersections, vertical and longitudinal slopes, and sight angles. In addition to the physical changes in the infrastructure regulations in the urban transportation system it is necessary to provide new standards and per capita transport space. To conduct the reforms, town building engineers suggest that up to 30% of the urban land shall be allocated to the network of streets [34]. The field observations showed the need for wider streets, larger stations, sidewalks, and service offices to avoid overcrowding. Therefore, the Chabahar transportation system should increase the per capita land allocated for the urban transportation infrastructure network. In particular, it should build a modern international airport, a train station, a logistic center, and a new port for cargo and passenger transport.

Our case studies showed that the topographical and environmental conditions of Chabahar require special attention to the design of the network. The emergence of international and intercontinental corridors requires a new intra-city transportation system to improve connections with the surrounding towns. The graph in Figure 3 exhibited the traffic from near towns, 1440 cars in 12 h, to Chabahar as compared to other origins. The graph showed that 292, 1873, 144, 72, and 1512 cars interned into Chabahar from W, F, K, R, and L origins, respectively. Since the beds of the streets in the Chabahar plain are flat, it is possible to watch the landscapes with necessary care in the design of the streets without damaging the horizon. It is also possible to make the city more attractive with beautiful streets. The new design will improve the environment with climate-appropriate trees to combat climatic difficulties. Bicycles shall be on the agenda of the re-planning to install suitable lines for cyclists. Transportation infrastructure network planning in the city means coordination between transportation and land policies [35,36,37]. Our optimal plan protects the environment and natural and economic resources. Furthermore, the Chabahar transportation system needs legislation on the rights of passengers, to reduce accidents, and to have accurate travel schedules and management.

The transportation infrastructure network of Chabahar needs several reforms in terms of widening the streets, connecting passages, widening sidewalks, correcting street slopes, and improving sidewalk slopes. It requires the reconstruction of water canals and corrections in the geometry of intersections and squares. It also needs larger bus and taxi stations. The train station shall be connected well to the urban street network and airport. We shall plan and design parking places near the train and bus stations, the airport, and the port. Figure 5 exhibits places where the above-mentioned geometric corrections and other reforms shall be performed.

Considering the results from the case study on the transportation network system of Chabahar, including the sidewalks, streets, street intersections, plazas, and squares, in Figure 5 the physical and geometric corrections and groundwork are as follows:

• Sidewalks in all streets, including Belt Road, South Belt Road, and the streets of Ghods Tohid, Resalat, Abazar, Rigi, Baluchistan, Khomeini, Mostafa Khomeini, Sayad, and Municipality require geometric corrections to become wider. The sidewalks also need groundwork to adjust their slopes and flooring;
• All streets in Figure 5, including Belt Road, South Belt Road, Ghods, Tohid, Resalat, Rigi, Abazar, Baluchistan, Khomeini, Mostafa Khomeini, Sayad, and Municipality streets, require geometric corrections to become wider with better flooring and suitable slopes;
• We shall design cycling lines on all streets in Figure 5, including the Belt Road, Tohid, Rigi, Resalat, Abazar, Baluchistan, Khomeini, Mostafa Khomeini, Sayad, and Municipality streets;
• We designed surface water disposal channels on both sides of the street with a suitable longitudinal slope in all streets in Figure 5, including Belt Road, South Belt Road, Ghods, Tohid, Resalat, Rigi, Abazar, Baluchistan, Khomeini, Mostafa Khomeini, Sayad, and Municipality streets;
• Allays between the streets are very narrow without sidewalks. The alleys that remained from old times shall have wider places for cars and pedestrians. These are the parts of the city that require rebuilding with other programs, as engineers voiced earlier [22];
• Large Sea Street, Sayad Street, Mostafa Khomeini, small alleys in the Baluchistan district, and curvy avenues in Figure 5 require redesigning in sizes and geometrical shapes;
• Access to the free zone and then to the airport, the terminal for the near cities, the Bahman terminal, Baharan Park, and Rock beach with vast and beautiful standard streets and walking and cycling lanes should be designed and provided;
• All intersections on the mentioned streets require geometric correction to make a standard safe sight angle for drivers there;
• Urban squares on the Belt Road, South Belt Road, and streets of Ghods, Resalat, Baluchistan, and Rajaei need geometric corrections to provide the adequacy of dimensions for easy access, traffic distribution, and attractiveness;
• Pedestrian bridges should be built at every 1000-m distance on the Belt Road, Ghods, and Rigi streets with suitable flooring, considering the elderly and the physically disabled;
• Every new design on the mentioned streets, alleys, plazas, and intersections shall mark an increase in the quality and safety of pedestrians.

In addition, when planning to improve urban transportation, a question about which system is suitable for the particular features of this city arises. This paper, according to the field studies and experiences in the world [38,39], introduces a public transportation system with bus and minibus lines. We need a public transport network throughout the city. Figure 6 shows our suggested public transport network system with bus and minibus lines.

Figure 6 shows two types of bus and minibus lines in Chabahar to supply a simple public system for the needy local people. The conduction of the above-mentioned reforms will adopt the urban transportation system of Chabahar with the international corridors. Additionally, the outcomes of the reforms will improve the sustainability in the region with economic prosperity and improved quality of life.

4. Findings and Discussion

A literature review of the coordinated development of the transportation network and the international corridor through that city showed that this subject has not yet received enough attention. This article, with its practical nature, for the first time examined the opinions that emphasized the following points:

✓

Transportation systems are constantly evolving multidimensionality [1];

✓

The expansion of regional and international trade relationships led to the development of transportation networks;

✓

In the intercontinental corridor plans, attention is not paid to the potential transportation of cities that the corridors pass through;

✓

Transportation infrastructure networks need increased per capita land use [40];

✓

Sustainable strategic plans should decline pollution caused by the urban transportation system [17,18,19].

We have conducted a case study strategy to re-design Chabahar’s transportation network system with the new requirements and its particular situation. We have observed that Chabahar’s narrow streets and initial transportation system cannot service the new needs caused by the Chabahar–Milak corridor. In the eight centers of Chabahar city, we observed travel behavior from 8 a.m. to 8 p.m. During this time, a team of observers took statistics from passing cars and asked about the reforms they wanted. Using graph rules, we simulated the collected data with the characteristics of Chabahar and discovered the following deficiencies:

✓

Streets and alleys have been constructed in recent decades without plans for organic daily needs;

✓

The narrow streets created by spontaneous development are for the needs of the earlier small populations without cars;

✓

The land allocated to streets is less than 16.5% of the total urban land areas, 380 of 2300 hectares. According to the United Nations principle, a street network should cover at least 30% of urban land;

✓

Chabahar has not allocated enough land for sidewalks, terminals, stops, and transport offices;

✓

Chabahar has no new models of the physical structure and infrastructure networks to adapt to the international/intercontinental corridor systems;

✓

Sight distance, including stopping and passing sight distances in the intersections, squares, and corners are unsuitable;

✓

Level and non-level crossings and pedestrian abutments at intersections are uncoordinated;

✓

Slopes of streets, sidewalks, and cross-sections in vertical and horizontal curves are incorrect;

✓

Streets and sidewalks have not been covered by acceptable standard flooring;

✓

Chabahar lacks an urban public transportation system.

According to the opinions of scholars and field experiences, we admit that discovering the straight and simultaneous relationship between the sustainable operation of the regional corridor and urban transportation of cities on its path is an important contribution to research for planning and designing future sustainable transportation systems. To solve this important problem, we use the gravity model to find the number of travels or the weight of cargo on the urban nodes and lines. The gravity model is a classic and tested mathematical procedure used earlier by professors [27,28]. Travel behavior analysis using a gravity model and a graph technique determines necessary geometric adjustments on the required links, nodes, and intersections. With this model, we found the number of cars traveling on every street. The graph in Figure 4 shows the number of cars in and out of every node. A total of 13,420 cars on the network is a considerable number for a city with inefficient infrastructure that will also experience a rush of travelers from other regions. Only the node of H hosted 5178 cars in 12 h. We now recognize that the transportation system of Chabahar is rudimentary and cannot take on the duties of an international city. Therefore, we have suggested Figure 5, which shows the observed infrastructure network. Names of the needed places for new designs and changes are on the figure. In the following, the types of required changes are introduced.

Changes in the design of streets, alleys, squares, sidewalks, intersections, slopes, viewing angles, and flooring are among the suggestions of this article. The meaning of the physical and geometric changes mentioned in Section 3.2 of this article is planning for a modern urban transportation system suitable for new services and with less environmental pollution. For this reason, we insist on building a public transportation system with the help of car lanes (Figure 6) and special areas for cycling. Our model presented in Equations (1)–(10) can be simulated in cities on the routes of international corridors everywhere.

5. Conclusions

This paper noticed that the sustainable function of intercontinental corridors requires improving urban transportation in cities on its route quantitatively and qualitatively. The analyses showed an increase in cargo and passenger transportation related to the international cargo and passengers passing the Chabahar. This paper aimed at adapting the urban transportation system to the requirements of the corridors. The research method was to learn from the opinions of scientists through literature reviews, case studies, and observations of eight travel origins in Chabahar. This method observed travels in the eight origins and destinations to measure the number of passing cars and to determine the traffic characteristics on the streets of Chabahar. We explored the opinions of urban managers and passing car drivers concerning necessary reforms in the infrastructure. We built a mathematical model by the gathered data, gravity, and graph technique. The model presented in Equations (1)–(10) has been simulated in the Chabahar urban transportation network. The model calculated the capacity of traffic on every street in the network. Considering the current shortages of the city’s infrastructure and the ever-increasing transportation needs arising from the Chabahar–Milak corridor, we proposed several renovations. The reforms should improve the geometric shapes and sizes of streets, sidewalks, squares, intersections, and the city’s public transportation network with the new applications. The place and type of every proposed change are visible in Figure 6. The reforms in the urban transportation infrastructure network would strengthen the position of Chabahar as a node in the corridor system and ensure the sustainable transport flow of passengers and cargo in the region. The innovative focus of this paper on the direct and simultaneous relationship between the sustainable function of the Chabahar–Milak corridor and the urban transportation of Chabahar on its route contributes to knowledge planning and designing sustainable transportation systems. The outcome of this paper contributes to detailed research on the exact sizes of transport spaces in the infrastructure network of cities located on the route of international corridors, including Chabahar.