2.1. Overview
Our evaluation of the impact of mobility restrictions on the population and the environment was based on a scientific methodology that can be reproduced and applied to other kinds of mobility restrictions, such as those related to natural or man-made disasters. The methodology includes the following three phases.
The first phase concerns data collection about the inter-urban mobility infrastructure and restrictions. Data was collected from different sources, mainly from governmental authorities and non-governmental organizations (NGOs). In the future, this could be extended to social media and mobile crowdsourcing.
The second phase uses network analysis to determine the best route [
14] under two conditions: the absence of mobility restrictions and the presence of those restrictions.
The last phase analyses the impact of the mobility restrictions on (i) the population, with a focus on increases in route length and travel time, and (ii) the environment, with emphasis on the additional energy consumption and greenhouse gas emissions.
The following sections will present this methodology in detail through its application to the Palestinian territory.
2.2. Data Collection
This research was based on data related to physical infrastructure, community mobility, and mobility restrictions. The collected data were integrated into a Geographic Information System (GIS) that provided a spatial illustration to support analysis of the mobility restrictions.
Figure 1 summarizes the types and sources of data collected. Road network data were obtained from the last updated version of the 2018 geodatabase of the Palestinian ministry of transport (MOT). The data came in a shapefile with categories including road name, number, width, and type. Mobility restriction data, including the separation wall and checkpoints, were obtained from the Geospatial web mapping application of the ministry of local government (Geomolg) [
17]. Geomolg is an open-source application that provides the ability to downloading the target layer in the form of a shapefile for any location.
Due to the lack of data on community commuting, individual vehicular emissions, and waiting time due to mobility restrictions, the study used data from a field survey conducted by the Applied Research Institute-Jerusalem (ARIJ) [
18]. The survey concerned checkpoints distributed in different locations in the West Bank. It employed 70 vehicles (cars, taxis, buses, and trucks) with tracking devices (GPS) for a period of 6 months (January–July 2018). More than 18 million records were registered.
Table 1 summarizes the average delay time recorded in this survey at the main checkpoints in the Palestinian territory. The delay ranges from 23 to 89 min, with an average value of 49.5 min. This research was conducted with the average values, which constitute a limitation for this research. In the future, mobility data could be enhanced using crowdsourcing, including social media and mobile applications [
19,
20].
Most data were obtained in shapefile format in the shape of polygon or line, which includes attributes labeled in different fields (
Table 2). All the shapefiles have two common fields: (i) ObjectID, a unique, non-null integer field used to identify rows in tables in a shapefile, and (ii) Shape Length, which is used to store the calculated geometry of lines or polylines lengths. For example, in the attribute of polygon data (Qalqilya governorate border and Palestinian communities), a table called “Shape Area” stores the calculated geometry of the polygon area.
The shapefile for the Palestinian communities also has the “Community Name” attribute. The separation wall shapefile includes the attribute of the “Status” of the wall (constructed, under construction, and planned). The WB Road network shapefile contains an attribute “Status” of the road segment, either paved or unpaved, and “Road Type”, to define the classification of the road network (local, regional, main, internal, and settlement).
The collected data then needed to be prepared. This phase consisted of three steps: (i) the creation of a geodatabase; (ii) the construction of the network topology; and (iii) building the network dataset.
A geo-database is the native data structure used in ArcGIS and is the primary data format used to edit and manage the data. A Geodatabase can be a personal, file, or enterprise [
15]. A personal Geo-database was created using ArcGIS 10.1, which operates a database that can store, query, and manage spatial and non-spatial data and contains data on the separation wall, road network, and communities.
For accurate analysis, it is necessary to build a topology of the road network to discover errors in the data and correct them. This was performed by applying topology rules in order to ensure that there were no dangles in the road network, and that the roads did not intersect or overlap.
Creating the road network dataset required a geodatabase containing a line feature class stored in a feature dataset. The network dataset consisted of the set of edges representing the links over which agents travel and the set of junctions which connect those edges and facilitate navigation from one edge to another.
2.3. Network Analysis: Best Route Analysis
The best route can be the quickest, shortest, or most scenic route [
15]. For example, if the impedance is time, then the best route is the fastest route. Hence, the best route can be defined as the route that has the lowest impedance. In this research, the impedance is the distance, so the best route is the shortest route.
Different methods have been proposed to analyze the impact of natural or man-made events on urban mobility. For example, Huang [
21] used a hazard graph model to study the spatial pattern of flood impact on urban mobility performance using space syntax theory. Ghandour et al. [
22] provided a visual analysis of safety hazards on the roads network in Lebanon using spatial autocorrelation and spatial clustering theories such as the Global G method, Getis–Ord, and Hot Spot Analysis. Ahmed [
15] used network analysis to identify the best route from an incident to any healthcare service providers in the Greater Cairo metropolitan area. Other models have used time-series data to predict future hazard trends on road networks. For example, [
23] employed the Autoregressive Integrated Moving Average (ARIMA) model to explain and predict the trend of traffic crashes in Palestine. Finally, Dsca et al. [
24] used Dijkstra’s algorithm and the Global Positioning System (GPS) to determine the accumulated cost between any two nodes of a road network. Since this method is simple and well adapted to existing data, it was used in this research. This method has been used recently by [
25] to find the shortest path for tsunami evacuation. [
26] highlighted the capacity of Dijkstra’s develop an algorithm to find the shortest route from a given vertex to any other vertex. Based on previous research findings [
24,
25,
26], Dijkstra’s algorithm was used in this research because of its simplicity and ability to find the shortest route between any two locations in the Palestinian territory.
2.4. Impact of the Mobility Restrictions on Travel Time and Delay
The impact of the separation wall on the mobility between two vertexes was estimated using the difference between the route in the presence of the wall (D
W) and the route without the wall (D
0). The increases in the route length (ID
W) and in the transport time (TD
W) due to the wall were calculated as follows:
where AvS denotes the average traffic speed.
Checkpoints have different forms: permanent checkpoints, partial checkpoints, road gates, earth mounds, road barriers, and controlled tunnels. The time delay due to checkpoints (TD
CP) was obtained from [
18].
Table 1 summarizes the average values of this delay at the main Checkpoints in the Palestinian territory.
2.5. Impact of the Mobility Restrictions on the Population and the Environment
The additional travel time due to the mobility restrictions (TD
tota) is equal to the sum of the time delay due to the wall (TD
W) and that due to the checkpoints (TD
CP):
The impact on the environment concerns both energy consumption and greenhouse gas emissions. The determination of the additional energy consumption due to the separation wall (E
W) was carried out as follows:
where n designates the number of vehicles concerned by the separation wall, ID
wi is the additional distance of vehicle i due to the separation wall (Equation (2)), and ECm
i denotes the energy consumption per km of vehicle i.
The calculation of the energy consumption due to the checkpoints (E
CP) was carried out using (Equation (5)):
where TD
CP is the time delay at the checkpoint and ECs is the rate of energy consumption of idle or slowly moving vehicles.
The CO
2 emissions due to the separation wall (CO
2W) and to the checkpoints (CO
2CP) were determined from the related energy consumptions as follows:
where CO
2Fi is the CO
2 emission factor of vehicle i, which depends on the type and energy use of the vehicle.