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Examining the system and the results Essay

Examining the system and the results Essay

Specific rules are also taken into accounts which affect the speed of an ambulance vehicle such as number of lanes, number of traffic lights, restricted access, presence of schools, street markets, the width of the road and conditions of the road surface. Each road within the logical network was given a weight according to the different rules mentioned above. This weight is a numerical value that is used along with travel time costs (speed limits and lengths) in order to find weighted travel time costs which consider all the rules that could affect the speed of the vehicles in reality.

For example, if a road has one lane, it will be given more weight than the two lanes road. The travel costs of these roads are then re-calculated by multiplying the weight with the travel cost. As a result of this procedure, the calculated travel time (weighted) will be higher in one lane road than two lanes road; i. e. one lane roads will be inadvisable because a vehicle is expected to take much time to travel along these roads than the two lanes and will have an effect on manoeuvre ability of ambulance vehicles along these roads.

This procedure is then repeated for all other rules in order to find the travel time costs (table 7). The general rules which considers the day of the week and time of day are then integrated. This is done by adding other weights to the road, dependant on the day and the time, according to that the real travel time cost will be updated Two terms will be used when integrating the expert knowledge to the system, travel time and weighted travel time.

Travel time only considers the length and the speed of each road while weighted travel time considers both the travel time and the rules which have already been set from the experts. By assigning various weights (numerical value) to the roads depending on priorities of choosing one route rather than another, it is possible to achieve a more accurate travel time on the streets. This is done by multiplying the weights field to the travel time field to get another field that can be called weighted travel time.

Weighted travel times can be then used as the cost field ArcView Network Analyst to find the fastest route between two points. This system was examined by setting up several scenarios based on various times and rules collected from ambulance drivers’ knowledge in order to find the least time cost routes between an incident and a hospital location. As an example it seen that the ambulance drivers usually prefer two lanes roads than one-way 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 on the way.

Therefore different weights would be assigned to each of these roads in order to find the fastest route that considers the one-lane’s factor. The one lane factor in addition to other factors will be discussed in the scenarios below. Scenarios two, three and four integrates some of the expert knowledge while scenario one is used by norm navigation systems. A comment string field was added to the road network layer to detail the reason of giving such weight or the reason of giving a negative value to the travel cost field as seen in table 8.

This scenario calculates the least travel time route (fastest route) in minutes based on using the MINUTES field in the road which is calculated from distance/speed. The speed in here represents the speed limits in km/h. This scenario is used mostly by norm navigation systems such as Dell/Navteq GPS Navigation System in order to find the quickest path between two points. The response time was 3. 25 minutes in this scenario after converting it from hours (figure 4) and related attributes (table 9). Scenario two This scenario assumes that several streets of previous route exist within a school zone of 200 metres.

For example, between 1:30-2:30 P. M. this zone is predicted to be congested due the car parking and students crossing the streets. Therefore any street which falls within this zone will be assigned to a weight of 1. 1 while other values are assigned to 1. Then the weight field (weight1) is multiplied by the travel time cost field (MINUTES) to calculate another weighted travel time field (INCHES). As a result of this procedure the travel time will be maximised along these weighted streets as seen in figure 5.

The response time was 3.78 minutes as seen in table 10. Scenario three This scenario assumes that a roadwork is in progress, on one side of a local street at the same time as the previous scenario. This temporal data can be collected from the municipality periodically and update the system according to it. Another weight of 1. 1 is assigned to that street which will re-route the current path in order to avoid the expected delay time. In this scenario the response time was 3. 87 as seen in table 11. The re-routed fastest path is shown in figure 6.