Mesoscopic simulation models

Mesoscopic models consist of microscopic and macroscopic approaches to provide a high efficiency describing all key characteristics of the road. For example, if the drivers decide to change lanes, this is a microscopic aspect, while this decision should depend on the densities and speeds which are obtained from a macroscopic model.

4.4.2

Macro-simulation models

Macro-simulation models (Also termed Macroscopic) or (traditional transport models) are defined‎as‎“Providing an aggregated representation of demand, typically expressed in terms of total flows per hour”‎[173]. In other words, they deal with characteristics of the section of any road. Such models could be traffic engineering tools and transport planning tools, such as TRANSYT and OmniTRANS software. Macro-simulation models based on the continuum traffic flow theory; traffic flow theory is the description of the time-space evaluation of the variables; volume, speed and density [161] .

Macroscopic models are considered not computationally expensive. Despite the fact that large amount of data related to the network are required to be analysed, the simulation can be acceptable but may not be utilised in such huge and complex problems. In other words, macroscopic simulations fail to adapt to random and rapid changes in the environment [174]. Consequently, long sections, hundreds of miles, require high numbers of computation processes which cause increasing in time simulation, while microscopic and mesoscopic models were suggested to fit to simulate such traffic networks [172].

4.4.2.1 OmniTRANS software

OmniTRANS is an Integrated Multi-Modal Transportation Planning Package; it is an example of macroscopic vehicle modelling package. The main purposes of this software are:

 Project management information (which describes how the data are structured)

 Describe the data (networks, matrices, zones data etc.)

 Users defined selections of data (for example, describing city network variables, network links, and urban/suburban areas)

 Users defined specifications for reports and output plots

Typically, the software contains many templates, static assignment, dynamic assignment and transit assignment. This templates diversity helps the simulator to obtain different information. Furthermore, the project templates also contain common definitions, useful specifications and lists etc., that are passed from project to project.

The OmniTRANS software is a transportation oriented program which mainly deals with assigning traffic volumes into the available transportation network. The software is considered as a macroscopic approach which deals with the traffic volumes as a whole traffic and not a distinct vehicle. The major characteristics of the software are as follows:

 The software uses several transportation modes, like private vehicle, busses, light rail, motorcycle and bicycles.

 The transportation network links could be customized according to the actual status in the city network.

 The transportation network geometry is to be set according to the background satellite image of the city with an adequate scale.

 The nodes, links, and centroids of the transportation network are coded.

 The software implementation subroutine language called RUBY to conduct various jobs that contains the models used in the software, such as static, dynamic models etc.

The important entry data sets that are required within the dynamic modelling will be defined below, these input files could be grouped into the following categories:

1. The purpose of the trips should be defined; land use in the area to extract the O-D Matrix, these could be divided into

 Work

 Home

 Others

2. The type of transit transportation, the mode of the travel which could be divided into

 Roadway vehicle

 Bicycle

 Public transport (light rail train, bus, train and tram)

 Walk

3. Time of the trips along the daytime

4. The user type of the analysis (internal cordon, external cordon, through traffic from certain origin to certain destination)

5. The type of the assignment ( all or nothing: which means that all the demand vehicles go through certain links neglecting the link capacity, capacity constraints models, through selected links or areas)

6. Types of the constrains (costs, distance, time, waiting time, penalties, fares, number of passengers)

7. The iteration value

8. The transportation network geometry (link type) from freeways to major roads including rail, bus, bicycle, walk ways, and capacity.

9. Traffic facilities and projects like the intersections, roundabouts, tunnels and bridges. 10. The socioeconomic data in the area that to be entered in the O-D matrix.

11. The trip attractions and trip productions points.

12. Any counters and screen lines in the transportation network. Below, we will describe the running steps:

 First, downloading the OmniTRANS software is a top priority.

 Then, the user can simply draw the components of the network; these components are defined. The input data to the software includes the link characteristics, such as link length, road capacity, road layout, speed, the vehicles type, link type, the free speed and the design speed

 The O-D trip generation matrix for certain time of the day is applied at this stage.

 Then, the maximum capacity for the network should be determined.

 After that, a specific job is to be written using the software language. However, it should be noted that the above program is limited to only 25 zones. To overcome the OmniTRANS limitation, a model was developed; called NETRASOFT. The most of the main functions (except the visualization and network map user interface) in the OmniTRANS package can be carried out by NETRASOFT [175]. This latter software has considered the Lighthill - Whitham - Richards (LWR) model. Although, the development new package has the ability to analyse for unlimited network size, still there is a difference between the two software programs above. The main difference is the calculation of the travel time [175].

In summary, the geometric traffic data represented by O-D matrix has to be collected, then the population data. Subsequently, the O-D matrix will be dispatched into the transportation network, assuming no accident happened. Then, after the incident attack, a new O-D matrix shall be generated for the purpose to guide people to the safe area. A dynamic scheme is applied and a snapshot is taken every 10 -15 minutes (the implementation details will be discussed in Chapter ‎6).

The people‟s response time to the event is taken and the average vehicle occupancy is considered (see Section ‎6.4). Finally, the total time for the evacuation process is calculated (the VANETs technology with the aid of virtual cloud infrastructure is employed here to increase the potential of minimizing the total evacuation time and hence increase the opportunity to receive/send the emergency messages between the drivers and the control management unit).