2.5. Influence of the dynamic load
In this work, and contrasting with some previous works in this area mentioned in Section 1, the studied system is given one more degree of freedom by allowing the vehicle load to vary along the waste collection trip as such variation can contribute with up to 20% of released hot emissions (Hickman et al., 1999). The vehicle load is considered to change each time the glass-waste from a different container is uploaded, which influences the fuel consumption and pollutant emissions on the subsequent road section travelled.
For the sake of the results intelligibility, the study of the dynamic load influence on fuel consumption and pollutant emissions is performed by virtually locating the sorting station closer to the collection area than it is in reality. This was done in order to minimize the potential impact of the considerably long distance between the sorting station and the first container visited (and between the last container visited and the sorting station in the way back – see Fig. 1), once the actual dynamic load effects could be concealed by the dominating effect of global fuel consumption at this part of the collection round trip.
This influence study is performed for one of the new established circuits consisting of 50 ecopoints. First, the vehicles routes are optimized for the shortest time and the fuel consumption is calculated assuming that the glass-waste volume uploaded at each visited eco- point is constant and equal to 1 m3 (i.e. the actual fill-up rate of the containers was not considered in this case) – the baseline case.
Then, two contrasting scenarios were designed to perform the simulations that yield the dynamic load effects on the fuel consumption and pollutant emissions, considering an exponential distribution of the collected waste amount along the collection route. The first scenario assumed that the collected volume of waste increases exponentially along the collection route, whereas the sec- ond scenario assumed the exponential decrease for the same route. This means that the volume of glass-waste added to the vehicle case at each ecopoint is exponentially more (or less for the second scenario) than that of the preceding ecopoint, assuming that all the material in the container is always unloaded and transferred to the collection vehicle. Both scenarios keep invariable the total waste volume collected per route and the sequence of visited ecopoints, i.e. they are the same as those obtained in the case of the constant load (the baseline case).
These exponential increase or decrease was considered in order to clearly evidence the dynamic load effect. The reason is that its contribution is much less evident than that of the route optimization.