1 Introduction

The lack of reliable and sufficient energy resources, and the environmental damage caused by excessive use of major energy sources like coal and oil are the two main challenges the world is currently facing [1]. Society depends on energy to maintain the current standard of living and to support multiple aspects of our economy [2]. Renewable energy plays a key factor in protecting the environment, leading to a reduction in the burning of fossil fuels by generating electricity with solar or wind energy [3]. One obvious manifestation of today's consumer society's infernal aspirations is the round-the-clock, brisk transportation of heavily loaded vehicles on modern highways [4]. Chemical energy is used to supply the mechanical energy required to move [5]. The mechanical energy that is generated within the transportation system, and manifests as friction energy, potential energy from weighted cars, heat energy arising from tires in contact with the road, sound energy from vehicles, and other sound produced on the road, as well as the strong waves of wind energy produced when traveling at high speeds [6], are untapped resources [5].

Journeys by car account for 92% of all transportation-related CO2 emissions [7]. To maintain effective and sustainable traffic operations, intelligent traffic control at urban crossings is essential. Urban crossroads are notoriously congested and represent danger when driving. Poor traffic control at such locations can create a number of problems, including increased fuel consumption, environmental pollution, delays, long queues of vehicles, slower travel times, etc. [8]. In contrast, traffic flow arises when a group of vehicles is connected by general intent and facilities locally assist in realizing them [9].

Al-Baha region’s urban development and mobility system includes main highways linking it to the Makkah region and the Asir region. Frequent rock failures occur along a 30 km section of the mountain road that runs alongside the Al-Baha descent, usually during rainy seasons. Wedge, planar, toppling, and rockfall failures comprise the majority of failures in both the naturally occurring and artificially created rocky slopes [10]. The road hierarchy of Al-Baha city and its mobility system can be consulted to describe energy generation through vehicular movement. It is essential to exploit the transportation system and vehicular movement along the main road, due to its capacity to generate energy via wind and solar radiation. The potential for Piezoelectric energy harvesting has advantages over other alternative sources, due to its large power density, ease of application, and potential for fabrication to suit different macro energy generation scales. A specific approach is vital to determine the extent to which energy can be generated this way, how the generated energy can be used and its impact environmentally and economically. Hence, this study is divided into five main categories; (1) introduction, (2) case study overview, (3) methodology, (4) results and analysis; (5) discussion and (6) conclusion and recommendations.

2 Methodology

Al-Baha city needs a combined approach to determine the road hierarchy and mobility system in terms of urban traffic planning, how environmental benefit can be achieved and the potential services that can be applied. The hypothesis of the research is that, the traffic jam in many locations resulting high pollution from CO2 emission and essential need to have road hierarchy system for Al-Baha region with alternative transportation systems for environmental prospective. Hence The approach was designed to answer the questions below:

  1. (a)

    What is the traffic capacity in the Al-Baha region and what are the potential effects on the local environment?

  2. (b)

    What is the road hierarchy in the Al-Baha city and what are the weaknesses of the main roads to other cities?

  3. (c)

    What transportation methods are currently used in Al-Baha and what transportation could potentially be used to provide the main services in Al-Baha?

2.1 Site visit and traffic survey

It was essential to select locations across Al-Baha city to determine the characteristics of the main highways that carry a high number of vehicles. Al-Baha city has four main highways that provide connections between Al-Baha city and the southern regions of Saudi Arabia, one highway that links Al-Baha city to Makkah region of Saudi Arabia, one that provides links from the airport to Al-Baha city, and another within the city center connecting the main populated zones. Figure 1 is an Al-Baha city map detailing the points chosen for the traffic survey. Site visit survey to estimate the traffic size in four different locations across Al-Baha. This survey includes rush-hours time (between 6:30 to 8:00 am and between 1:30 to 2:45 pm) in working days from Sunday to Thursday and non-rush hours out of rush hours times as well as in weekends. The survey method for the traffic survey involved calculating the number of vehicles travelling between each selected point. The survey includes:

  • Traffic survey in rush hours This survey targets the number of vehicles and movement both ways during the rush hour. Rush hours in Saudi Arabia are from 6:30 am to 8:00 am and between 1:30 pm and 2:45 pm, corresponding to work and school travel times.

  • Traffic survey in normal hours This survey targets number of vehicles and movement both ways during normal hours on week days; i.e. all times not listed above as rush hour in the working week.

  • Traffic survey at weekends and times This survey targets number of vehicles and movement both ways during weekends and vacation periods. These days experience higher levels of traffic than non-rush hour times in the working week. Traffic would be expected to vary between cities, depending on facilities such as restaurants, shopping centers, malls and other attractions.

Fig. 1
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Selected locations

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Estimations of traffic capacity for the main highways in Al-Baha city were performed by benchmarking the traffic capacity in all of the three periods selected.

2.2 Expert consultation

This study presents proposals to develop a transportation planning system for the Al-Baha region. Experts from a variety of backgrounds will be consulted, and will share their experience and knowledge of the Al-Baha region and potential challenges. The expert’s panels will involve specialized who have background in built environment and civil engineering from the ministry of the municipality for the Al-Baha region, the ministry of transportation for the Al-Baha region and academics and faculty members specializing in engineering in the Al-Baha region. In addition of their background, the criteria for selecting expert panelists is their knowledge and experience about of the Al-Baha region, as well as knowledge of challenges facing the transportation system.

3 Result and analysis

The analysis covered four main locations within Al-Baha city, all of which had highways and heavy traffic jam. Each location estimates the number of vehicles moving in both directions in normal hours, rush hours and at weekends. Figure 1 presents the map of Al-Baha city showing the four locations studied. The map was provided by the ministry of the municipality of the Al-Baha region and shows land use, forest area and main roads. This map will be used to understand the typology of urban planning of Al-Baha region, the road hierarchy based on geographical challenges and how the city has developed among mountain and forests.

  • Location one Traffic survey and analysis

The first location is on the highway from Al-Baha central to Taif city, and is well known for high capacity and traffic jam conditions. Figure 2 presents the map of the location, specifies the road width while Table 1 shows the traffic analysis in this location in rush hours, non-rush hours and at weekends. This location is a known hot spot for static traffic, due to its role linking Al-Baha city and other villages in the north of the region, as well as Taif city. The presences of a number of commercial facilities nearby, and the width of the road may partially explain this issue.

  • Location two Traffic survey and analysis

Location two is within Al-Baha city and has a high density of traffic due to its proximity to urban facilities. The location is beside one of the most famous public parks in the Al-Baha region. This park plays a significant role in local tourism and is one of most attractive facilities in Al-Baha. Therefore, traffic jams arise and impact the environment due to the high number of vehicles. The survey was undertaken during the rush hours, non-rush hours, and weekends and holidays. It can be seen that in Fig. 3, the map of the location presents the road connection while the details of the survey analysis for this location are presented in depth in Table 2.

Fig. 2
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Map of the location one

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Table 1 Traffic analysis in location one
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  • Location three Traffic survey and analysis

The third location is within Al-Baha city and also has a high density of traffic as the route directs the public to their destination before arrival at Al-Baha University. This location can experience traffic jams, especially in rush hours, as most of users are accessing the university, as it is one of the most attractive facilities in the region. In non-rush hours and holidays, the number of vehicles drops down by over 50%. This shows how the university has a significant impact of the congestion in that area. It is important to provide an alternative transportation system here, in order to develop the urban planning system, reduce CO2 emissions and protect the environment. Figure 4 display the map of the location, specifies the road width and Table 3 below provides the traffic analysis for location three.

Fig. 3
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Map of the location two

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Table 2 Traffic analysis in location two
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  • Location four Traffic survey and analysis

Finally the fourth location is in Al Aqiq town between Al-Baha University and the region’s Airport. The analysis confirms a high density of traffic, due to the link between the airport and Al-Baha, as well as the university’s location within this area. Figure 5 presents the map of the location, specifies the road width while Table 4 below shows the traffic analysis for location four. It is apparent that the number of vehicles is lower when compared with other locations. This location has an important role in local transportation and one of busiest roundabouts due to it linking the Airport to Al-Baha city and Aqiq town.

Fig. 4
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Map of the location three

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Table 3 Traffic analysis in location three
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Fig. 5
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Map of the location four

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Table 4 Traffic analysis in location four
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3.1 Traffic classification

Traffic data has been classified, which presents the challenges faced in some locations. It can be seen that in Table 5 below the details and challenges faced in all the locations during rush hour, in order to afford decision makers the flexibility to prioritize solutions and resolve traffic planning issues and protect the environment from CO2 emissions.

Table 5 Challenges faced in all locations during rush hours
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3.2 Benchmark traffic flow in the four selective locations

The capacity for number of vehicles varies between locations, based on the number of attractive facilities. Traffic issues have been observed for their impact on the environment at different locations in Al-Baha. The analyses should focus on the influence on local context and environment in different locations when comparing these locations. Figure 6 illustrates the number of vehicles in rush hours and non-rush hours for all four locations.

Fig. 6
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Number of vehicles in rush hours and non-rush hours at all four locations

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3.3 Expert’s opinions

A consultation approach has been conducted by the author to involve 12 experts who specialize in urban transportation, urban planning and civil engineering. Their contributions are weighed to suggest scientific solutions to develop urban transportation for Al-Baha region under the light their experience. Figure 7 below summarizes the specialisms of the expert panelists.

Fig. 7
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Overview of expert panelists

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In addition, the expert panelists are either academics from Al-Baha University, decision makers from municipality of Al-Baha, or government experts from other sectors. It is anticipated the interviews with these experts will lead to solutions from an academic perspective, considering site challenges and decision makers’ experience. The academic contributors are from the faculty of engineering, and the additional six expert panelists work for the municipality of Al-Baha province or other sectors such as other municipalities, Region Development Authorities in Saudi Arabia. Figure 8 below shows the backgrounds of the expert panelists.

  • Solutions ranking

Many solutions can be applied for the Al-Baha region to reduce CO2 emissions caused by transportation. The main categories relate to alternative transportation methods and alternative urban transportation approaches. Table 6 below illustrates the ranking for transportation solutions encompassing environmental and urban issues. The experts have been evaluate the importance of each solution from 1 to 5 and the result can be seen below.

Fig. 8
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Affiliation of expert panels

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Table 6 Ranking of transportation solutions to address environmental and urban issues
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The evidence clarifies that providing additional transportation options will minimize CO2 emission rates by reducing the number of vehicles. Furthermore, alternative transportation methods will solve the urban transportation issues related to traffic congestion. Road hierarchy and modification of land use to limit commercial sites will also help to manage urban transportation issues. Indeed, road and bridge design and spatial distribution of attractions are known as strategic solutions to manage urban and environmental transportation infrastructure.

The experts evaluated different methods to solve urban transportation issues and protect the environment from CO2 emission rates. These methods can be developed and applied for the Al-Baha region based on traffic and transportation conditions. Figure 9 offers some solutions relating to urban transportation and its effect on the environment. The experts underlined how important lowering CO2 emission rates from vehicles is worldwide. Possible options mentioned were using intelligent traffic lights to reduce congestion, and ensuring roundabouts are a minimum 15 m in diameter in the Al-Baha region. Additionally, Al-Baha region has one main highway connecting the city with the southwestern region, and so using tunnels rather than traffic lights would reduce traffic flow problems.

  • Alternative transportation methods solutions

Many studies confirmed that, alternative transportation methods will reduce traffic congestion, provide additional options for consumers and minimize the number of vehicles on the road [11,12,13], minimizing CO2 emissions [14, 15]. Different transportation methods in this study were evaluated by expert panelists and considered for the Al-Baha region as displayed in Fig. 10. Public awareness of using public transportation methods and the provision of an efficient transportation system must be raised. In addition, connecting the towns in the provinces with a rail network would reduce traffic load especially on the main highway in Al-Baha. Furthermore, Al-Baha University and the regional airport are two attractive facilities that should be accessible via the local bus and train network. Within the town, avoiding traffic congestion and protecting the environment from CO2 emissions, by establishing a bus system for each province is vital, as confirmed by the experts consulted for this study.

Fig. 9
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Solutions related to urban transportation

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Fig. 10
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Suggested methods

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4 Discussion

Due to the result analyzed and determining traffic demand in Al-Baha city, it is essential to apply urban planning solutions and strategies to address environmental issues. On this basis, the discussion will cover the potential environmental effect arising from traffic jams, proposing urban solutions, and technical applications. Since air pollution has a significant influence on human health and even causes premature death, it is a major concern in today's society where automobile traffic in big cities is a contributing factor [16, 17]. Protecting the environment is a global responsibility and includes reducing the CO2 emission rates resulting from transportation. Global sales of electric vehicles (EVs) have increased layover significantly in the past decade [18, 19]. However, projections about EV production plans, supportive policies, and future sales trends are essential to ensure adequate energy supply [18]. Most climate scientists worldwide are concerned about changes associated with global warming [18, 20]. Evidence has led to calls to reduce carbon emissions including those from transportation [21, 22]. CO2-free flooding is an important encouraged oil recovery technique, showing great potential under various reservoir and fluid conditions [23, 24]. Most private vehicles make it difficult to implement effective measures to reduce energy emissions [25, 26]. Hence, high traffic load at particular points will increase the pollution resulting from vehicles including CO2 emissions. Air pollution affects a huge number of people worldwide, and air pollution was considered limited in some countries [27]. Air pollution concentrations in cities vary greatly over short distances of less than one km, due to unequal distribution of CO2 emissions and source changes [27, 28]. Conventional methods for monitoring contamination at fixed locations lack the spatial resolution required to describe human exposure and localized contamination hotspots [27]. Air pollution includes pollutants such as CO, NO, NO2 and SO2, and regulations are essential to manage congestion and avoid micro pollution in urban locations. Software tools can be helpful for decision makers and urban planners wishing to manage pollution in specific areas. To employee regulations to control air quality and protect public health, it is necessary to first develop an emissions inventory. Measurements in traffic tunnels allow for estimates to determine air pollution factors for vehicles in use under real conditions [29].

On the other hand, noise pollution is an additional factor associated with environmental pollution. Urban large scale areas in cities face increasing noise pollution problems associated with air pollution. Applicable software tools called “Geographical information systems” can be used for collecting, analyzing, and presenting noise data when analyzing locations and systems. This software can be extended to address user-specific challenges through deterministic and statistical maps [30].

4.1 Application of sensors for urban traffic survey

It is essential to use sensors for urban traffic surveys, to monitor the capacity of traffic in target locations. The results can then be analyzed and used to improve traffic management and the potential for energy generation through the mobility system. A sensor and a gateway node comprise the sensor network. The sensor node's responsibility is to observe the flow of traffic in a designated region using various instruments to measure physical traffic metrics such as flow, density, volume, headway, wait times, throughput, and pollution. All the traffic information from all the nodes is then gathered by the gateway node, which sends the data to the base station [31] as depicted in Fig. 11.

Fig. 11
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Application sensors for traffic survey [31]

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5 Suggesting solutions

Al-Baha city is characterized by the topography of its mountains, which have cooler climatic conditions and are suitable for agriculture [32, 33]. This has led urban planner to develop the region for agricultural purposes, emphasizing the protection of forests and wildlife. Rapid urbanization and the uncontrolled rise of cities has resulted in various microclimatic changes, the deterioration of infrastructure, and the loss of agricultural land, water bodies, and open areas [34]. There are many solutions that could contribute to energy reduction and minimizing CO2 emissions in the Al-Baha region. Table 7 below presents seven urban transportation strategies to improve the mobility system and reduce CO2 emission rates through vehicles.

Table 7 Urban transportation strategies
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5.1 Public transportation system for Al-Baha

The Al-Baha region has developed over the past two decades due to urban growth and the establishment of a central university in the region. This has resulted in urban sprawl and an increase in transport needs across the region. The additional number of vehicles is contributing to higher demand for fuel and more CO2 emissions. An efficient public transportation network could minimize the number of private vehicles on the road, reducing CO2 emissions [35]. It is important to note that no empirical study has looked at whether increasing public transportation reduces carbon emissions. The development of public transportation also supports the objective of environmentally friendly travel [36]. There are six main sectors that could be served by a rail network to reduce traffic across the region, as illustrated in Fig. 12.

  • Firstly The airport is the main gateway to the region and establishing a train station there is essential, due to the growing demand to meet the needs of tourists and visitors especially. The airport receives different numbers of visitors each day and this number increases at weekends and in the holidays. The train station can be linked to the other attractive points in Al-Baha city and other towns across the region

  • Secondly Al-Baha town center is an attractive point where the municipality and other governmental services are located. Establishing a central train station linked directly to the airport would minimize the CO2 emission rates from private transportation.

  • Thirdly Al-Baha University attracts people from multiple locations across Al-Baha. Al-Baha University is playing a significant role in urban growth and has over 24,000 students and over 3000 members of staff. The high population density on the university campus requires a transportation network, as use of individual vehicles to access the site results in high levels of CO2 emissions. Hence, adding a train station linked to the airport and Al-Baha city center would minimize dependence on private vehicles

  • Fourthly Baljurashy town center will need a train station linked to Al-Baha city center and the airport train station, as these two points will have high demand for transportation. A university link is also an option, but a link from the university to Al-Baha city center is already proposed to allow students and staff members to access additional trains from Al-Baha city center.

  • Fifthly Almandaq, which is located in the north of the region, is reached via remote villages that need access to a public transport network. Therefore it is essential to put a train station in Almandaq town center to connect inhabitants with Al-Baha city center and the university train station. The train station in Almandaq will allow people living in remote villages to use rail network to travel to Al-Baha and the university.

  • Sixthly Al aqiq is a town located in the east of the region and is also reached via remote villages close to the airport. It is recommended to have a public transport infrastructure connecting the town center to Baljurashi, Al-Baha town center and the university, as the villages in this district are at a greater distance from one another. The main destination would be Al-Baha city center and the university, although it is advised to link the train station to Baljurashi to provide more options and greater flexibility to allow the public to reach most towns.

Fig. 12
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Public rail network proposals for the Al-Baha region

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5.2 Incentives to use electric low energy vehicles

The manufacture of electric vehicles internationally is intended to support environmental responsibility and shield the environment from high CO2 emission rates [37,38,39]. With the increasing popularity of electric vehicles, how we travel and utilize energy are drastically changing. The current infrastructure for distributing electricity is being put to the test by the introduction of these vehicles [40]. Switching from existing vehicles that run on fossil fuels to brand-new electric vehicles is intended to control CO2 levels [41]. Methane, the main component of natural gas, has also long been seen as a convincing alternative for expanding the world's energy supply [42]. Meanwhile, environmental damage is increasing as a result of continuing emissions from conventional vehicles [43, 44]. As the number of vehicles grows, the introduction of vehicles that do not use fossil fuels is seen as a way to reduce the auto industry's dependence on oil and reduce pollutant emissions [45]. Such an option can be adopted to protect the environment in Al-Baha. Due to several financial and environmental advantages, it is recommended to reuse, recover, and recycle end-of-life cars [46]. Encouraging the public in Al-Baha to own economic cars can play a significant role in energy reduction and minimizing CO2 emission rates, as fuel consumption and CO2 emissions by hybrid electric vehicles are lower than those of conventional vehicles (CVs) [47, 48]. Undoubtedly, vehicle ownership will increase dramatically in future. If the growing demand for passenger cars is met by conventional vehicles, greenhouse gas emissions will also increase commensurately. Thus, it is vital to offer, and encourage the purchase of, hybrid and electric vehicles [49, 50].

5.3 Road hierarchy planning

The management of traffic is becoming more difficult due to the dynamic nature of road networks and the significant increase in traffic congestion. It is evident that the shortest path algorithm considering only road length is out of date [51]. The road hierarchy method is applicable to Al-Baha city, as it can be used to identify noise and congestion, and to facilitate recommendations and solutions to manage environmental impact. Al-Baha city has only one highway that connects the city areas and links to other southern cities and regions. In the past 10 years, the number of vehicles in Al-Baha has increased due to the new university and other facilities that have resulted in urban sprawl and local development. The capacities of the cities roads and transportation systems have not similarly evolved to effectively handle the volume of vehicles now using them. As a result of recent technology breakthroughs, a variety of intelligent transportation system products are now accessible to transport agencies, allowing the collection of data to control traffic conditions across the road network [52, 53]. Using technology to manage a transport network more efficiently requires an intelligent transportation system, applying integrated advanced monitoring, communications, computer, display, and control management technologies to increase system productivity, safety, and improve mobility [52].

5.4 Technical applications

Traffic congestion can be exploited as an advantage using new technologies. Application of new technology at defined points could add to energy generation resulting from the high level of vehicle movement. Many sensors are available in the industry to generate electricity from vehicle movement. These can be used to fulfil energy demands for lighting and other uses, reducing CO2 emission rates. Many studies have evaluated the likelihood of adopting a two-degree-of-freedom (2DOF) electromechanical model with a piezoelectric method as energy-scavenging devices for road applications. [54, 55]. Piezoelectric technology can be added to streets in the form of sensors to generate energy in the form of electricity. As traditional power sources are becoming ever more limited, it is beneficial to explore such unconventional sources of energy [56].

6 Conclusion and recommendations

The study focused on analyzing the urban transportation system in Al-Baha city and its impact on environmental pollution. The study covered the urban transportation system, road hierarchy and traffic jams in different locations throughout the city. A map of Al-Baha city was evaluated in terms of urban road hierarchy and facility management. Furthermore, a site visit and traffic survey were conducted at four key locations across the city to identify levels of traffic congestion and its impact environmentally and socially. The study found only one highway links the city with the other cities and the southern regions of Saudi Arabia, creating heavy traffic that results in pollution and other issues. Potential air pollution was also estimated in each location selected for study. Furthermore, some urban and technical solutions were suggested for environmental and urban development purposes. The paper concludes with the following recommendations;

  1. 1.

    The network hierarchy should be restructured for Al-Baha city to take into account the distribution of attractive facilities.

  2. 2.

    Application of geographical information system (GIS) is vital to manage the urban network system and transportation.

  3. 3.

    Sensors should be introduced for energy generation to produce energy in the form of electricity from traffic.

  4. 4.

    Highways should be built between Al-Baha city and the surrounding towns and villages.

  5. 5.

    Establish a rail network, connecting Al-Baha city, the university, the Airport and other towns and villages around Al-Baha city.

  6. 6.

    Establish a bus network within Al-Baha city linked to the university and private colleges.

7 Future work

Future work will focus on pollution from vehicles and its impact to environments of Al-Baha region. Estimating the size of CO2 emission rates from current transportation system and number of vehicles has been targeted by the author due to it will need a specific method and engineering mechanism. The impact of CO2 size through transportation environmentally will be discussed and suggest additional solutions to minimize CO2 emission rates.