The system was examined by setting up several scenarios based on various rules deduced from expert knowledge, in order to find the least travel time cost route between an incident and a hospital location. By assigning various weights (numerical values) to the roads depending on priorities of choosing one route rather than another by the ambulance drivers, a more accurate routing system could be achieved. For example, ambulance drivers usually prefer two lanes’ roads rather than one- lane. This is because it is hard for the drivers to manoeuvre on one-lane roads, especially when there is road’s congestion or car accident somewhere on the way.
Therefore different weights will be assigned to each of these roads in order to find the fastest route which considers the one-lane’s factor. The latter factor and other factors will also be discussed. Scenarios two, three and four integrates some of the expert knowledge while scenario one is used by norm navigation systems. Scenario one The procedure in this scenario is mostly implemented in ambulance navigation systems. This procedure is also used by other norm navigation systems such as Dell/GPS Navigation System in order to find the quickest path between two points.
This scenario calculates the least travel time route (fastest route) between a hospital and an incident scene based speed limits and lengths of streets (travel time = distance/speed) as seen in figure 2. The speed in here represents the speed limits in km/h. The response time was 3. 5 minutes. Scenario two This scenario assumes that several streets of the previous calculated route were present within a school zone of 200 metres. For example, between 1:30-2:30 P. M. this zone is predicted to be congested due to car parking and students crossing the streets.
Therefore any street which falls within this zone will be assigned a weight of 1. 1 (in the attribute table), while other streets are assigned to 1. A weighted travel time field are then calculated by multiplying the previously calculated travel time in scenario 1 with the assigned weights (travel time*weights). As a result of this procedure the travel time along the streets that fall within this zone will be maximised. Therefore, the fastest route calculation in Network Analyst will choose other routes during this period of time to avoid any possible delay of reaching the incident.
The response time was 3. 75 minutes. Scenario three This scenario assumes that there is a roadwork going on one side of the fastest route that was previously calculated in scenario two. The roadwork’s information can be collected from the municipality periodically and the system can be updated according to it. Another weight of 1. 1 is assigned to the street containing the roadwork in order to calculate a new weighted travel time field (travel time*weights). Therefore, the travel time along this street will be maximised.
As a result of re-calculation, the fastest route will re-reroute the path in scenario two in order to avoid the expected delay time along this street as seen in figure 6. In this scenario the response time was 3. 87. This scenario assumes that there is only one lane in the previous rerouted path and this street has two speed bumps. Hence, it is expected that the speed of vehicles would be reduced along this street. A weight of 1. 1 was given to this street. Then, an alternative shortest route is calculated to avoid the routes causing time delays.
In this case, the system has selected the same route as the one in scenario 2 because all other alternative routes have higher travel time than the route in scenario 2. All other rules which are acquired from the experts can be added to the system in the same way as shown in the scenarios. Different weights are assigned according to the priorities of the rules suggested by the experts. This evaluation compares between the results from this system and other norm navigation system such as Dell Navigation System.
The fastest (quickest) route between to points which are collected from both systems will be compared. The start point in Dell system represents the hospital while the destination point represents the incident. The quickest routes from Dell were added to ArcView in order to visually compare between the two routes as seen below. The response time for Dell was approximately 3 minutes while the expert system was 3. 5 minutes. The response time difference might be due to the different speed limits assigned to roads and/or different accuracy of road networks because of different road network providers.