Pre & post evacuation models

A number of programs are being implemented for different evacuation plans, and each evacuation approach selection depends on an unique method which can be produced according to different situation circumstances.

For pre-evacuation and post-evacuation stages, some traffic experts have selected the tools which are developed for general purpose and adapt them to evacuation conditions. While others preferred to select specific programs which are developed for an evacuation scenario.

In 2008, a comparison of 30 traffic computer programs based simulation models was conducted by Hardy and Wundelich. The comparison was based on the complexity of the system. Additionally, the study addressed the difference between the three simulation classes; Micro, Macro and Meso-simulation models [157], additional information about the models can be found in [10].

A few examples for each simulation model have been reviewed in the next sections; Sections between ‎4.7.1.1 to ‎4.7.1.1. However, the definitions of some simulation models and their classification in three levels have been presented previously.

4.7.1.1 Meso-scale models

An evacuation model has been developed, called DYNEV. It is a meso-scopic model developed by KLD associates [151] and [192]. However, it is based on the movements of platoons of vehicles rather than individual vehicles [152].

4.7.1.2 Macro-scale models

Some macro-level models have been developed to be used to support the real time evacuation decision makers, such as NETVACI, MASSVAC and CLEAR. The ability to supply the transportation information during the evacuation management is the reason for using these tools [157] .

In late 1970 and early 1980, a number of simulation models were developed to assess and address traffic emergency plans. In 1982, Youssef Sheffi et al., from MIT, developed the NETwork emergency eVACuation model (NETVACI) that addressed the estimation of clearance times, that is the time until the last vehicle or evacuee leaves the affected area, for areas surrounding nuclear power plants [151] and [184], it is a fixed-time macro-simulation model. This model used the traffic flow models available to simulate the evacuation process, which means the clearance time also, the model was able to calculate the total evacuation time until the evacuee reached the safe area. In this model, NETVACI works on assumption that the drivers select their route according to their prior network knowledge, called “myopic”‎ which means drivers will assess the traffic ahead.

The advantage of this model is the potential of simulating a large traffic network at modest computational costs. And, it has overcome the NETSIM micro-simulation model drawbacks [193], [188] and [194]. However, a few limitations have been reported regarding the use of NETVACI model, such as it is a deterministic rather than dynamic model. It did not make assumptions about evacuees‟ behaviour [184]. A limitation in applicability to hurricane evacuation is found. Also, the behaviour of drivers during the evacuation has not been considered [68].

MASSVAC is also a macro-simulation model which has been developed to apply to hurricane evacuations [195]. For the major road arteries, the MASSVAC macroscopic model is capable of estimating the evacuation time under different traffic and disaster severity conditions. The model drawback involves ignoring the time taken to reach the nearest major arterial road which affects the evacuation estimation time.

A macroscopic evacuation called CLEAR (Calculating Logical Evacuation And Response) model has been developed by KLD Associates [151]. This model was developed for the evacuation in the event of specific hazards, for nuclear regulatory commission, which require to set the model by considering the vehicle movement only along primary arteries, thereby reducing the computational burden [185].

It estimates the time required for clearing a certain disaster area for a specific population density and population distribution by simulating the movement of vehicles on a transportation network according to the conditions and consequences of traffic flow. The program also models the distribution of times required by individuals to prepare for an evacuation [151].

Other simulation models have been developed to be used particularly in emergency situations; such as EVACD and ETIS, for further information; see [196] and [197].

4.7.1.3 Micro-scale models

Traffic simulation techniques have been used since the early days of the development of traffic theory which provide the potential of positive usage of micro-simulation models to the analysis of complex traffic problems.

More recently, evacuation analysis requires a relatively fine level of traffic network details. First, many evacuation studies are employed for day-to-day traffic applications. The incident management system can be difficult to be evaluated using normal traffic theory as it requires more details regarding the situation whether it is dynamic, stochastic and most importantly is the driver behaviour.

For example, NETSIM is the earliest microscopic model, highway traffic simulation model. The model has been developed by KLD Associates, which is used for network researches as well as for evacuation planning [14], [15] and [179]. The model addressed the simulation of the traffic system of small urban networks under normal operating conditions, the model can handle 99 nodes and not more than 160 links and the maximum network occupancy does not exceed 1600 vehicles. In early 1980, the first use has been recorded by HMM Associates to estimate evacuation time for a nuclear plant area. However, its drawbacks include its capacity limitation to deal with large networks, and deficiency of dynamic route choice models [194]. Another drawback was reported by Yosef Sheffi [193], even for very small network implementation, the computational costs exceed tens of thousands of dollars. Furthermore, the modellers should specify the intersection turning movement which does not involve the dynamic route selection.

Hobeika et al. have developed and improved a mass evacuation computer program called MASSVAC, they developed MASSVAC 3.0 and upgraded it to MASSVAC 4.0. The model has been developed specifically to deal with incidents at nuclear power plants. The evacuation plan suggested evacuating people can be done in two phases, the first stage is that people evacuated from the a disaster area should be enabled to choose the shortest routes and then be directed to a safe area in the second phase, further information reported in [198] [199], [186], [195] and [200].

Another micro simulation model has been produced to analyse a large scale evacuation, called TEVACS [201]. The natural design of a transportation system is a combination of various traffic modes such as automobile, public transportation, motorcycles and bicycles that should be included in any model to address the problem effectively. In this model, each transportation mode has been treated as a universal unit called the PCU; Passenger Car Unit [186] & [201].

Some general traffic software packages are used also for the evacuation conditions; such as S- Paramics and VISSIM [14] & [24]. S-Paramics has been used also in emergency evacuation. They applied S-Paramics to obtain the clearing time estimates under various scenarios [186] and [184]. In 2008, VISSIM models were used to find the locations for access to the reversal flow lanes (contraflow) from normal flow lanes [202] and [184]. Liu et al. have used VISSIM as the online-simulation module of the proposed integrated emergency evacuation system [203] & [184].

In 1991, Southworth reported that a wide range of micro-simulation models addressed some of the critical problems at intersections such as delays, where the majority of delays occurred. Route choice is generally either myopic (drivers select the least congested link at each intersection) or restricted, drivers wandered aimlessly through the unknown streets as a result of emergency managers controlling the flow at each intersection. They have been used primarily in geographically limited urban network studies (for example, primary roads only), or in relatively small urban and rural area studies [185].

CORSIM and DYNASMART are also used in evacuation modelling, additional information has been produced at [204], [205], [206] and [184].