3.1 Interpreting the model and clusters
To understand the nodes on the map, the layers of the map and their clusters are interpreted below. In the end, the cluster interpretations across the layers are combined to provide the final interpretation for the cluster. These clusters are then used to provide the context for the manoeuvres.
3.1.1 Velocity Map
The code-map for Velocity layer is displayed in Fig. 6. The interpretation for each cluster is as follows:
Blue The velocities in these nodes increase gradually. Furthermore, they are always above the middle of the nodes, indicating above-average to high velocities.
Grey The velocities are decreasing gradually in these nodes. However, they appear to be close to the middle or higher, indicating high velocities.
Yellow The velocities are either decreasing rapidly towards zero or constantly zero.
Green The velocities are mostly at 0. Sometimes they decrease from a low velocity to zero or increase from 0 to a low velocity.
White These nodes contain a mixed set of velocity curves that are always higher than 0, however not as high as the blue or yellow cluster. The vehicle is not stopping in these nodes, but there are a few decelerations observed.
3.1.2 Accelerator Pedal Position
The interpretation for accelerator pedal position layer is as follows (Fig. 7).
Blue The throttling behaviour appears to be aggressive in these nodes. The throttling is mostly high and sometimes released rapidly.
Grey The driver is mostly releasing the throttle and sometimes just 0%.
Yellow In most cases, there were no throttling observed. Few nodes have a rapid throttle from 0 or released to 0.
Green These nodes are very similar to the Grey cluster.
White The nodes cover all other behaviours observed. Constant 0% nodes are also present, however fewer than that of green or Yellow. Additionally, a few taps on the pedal were also observed.
3.1.3 Brake Pedal Position
The observation of Brake pedal position variations (Fig. 8) is as follows.
Blue There was no braking in these nodes.
Grey There was no braking in half the nodes. In the rest, there was some gradual braking observed.
Yellow High brake usage was observed in these nodes, and most of them were rapid.
Green The brake pedal was completely 0% along the bottom. The remaining nodes have a brake release to 0 and the top most nodes have a rapid braking. However, the rapid press was still low than that of Grey cluster.
White Most of these nodes have no braking at all. A few nodes have rapid press or releases.
3.1.4 Distance covered and Fuel Consumed
Distance and fuel consumption are represented as sectors (Fig. 9). The observations are as follows.
Blue In comparison to other cluster nodes, these nodes have the highest fuel consumptions and distances coved.
Grey These nodes appear to travel distance slightly lesser than Blue cluster, but have very low or even 0 fuel consumption.
Yellow These nodes also have very low or zero fuel consumption. The distance covered is also low.
Green There is almost no distance covered in these nodes, but there are still small fuel consumptions observed.
White Low to average fuel consumption is observed. Distance covered is also low to average; however, they sometimes are not correlating at higher values of either.
3.1.5 Final interpretation of clusters
Based on the previous interpretations of the individual layer of the map, the final interpretations of the clusters are as follows.
Blue The driver had no intentions to stop the vehicle in the near vicinity, and the velocity is very high. Hence this cluster is termed as High-Speed Zone.
Grey The driver is slowing the vehicle, but not very rapidly. He is aware of a nearby stop or obstruction and hence is planning to stop gradually. Since the vehicle is running with less influence of throttle and brake, this cluster is termed as Coasting Zone. These nodes are good to have since they are very fuel-efficient.
Yellow These nodes also exhibit decelerations; however, they also have high braking. This implies the driver wants to stop the vehicle rapidly because of some circumstance and this manoeuvre is not fuel-efficient. The cluster shall be termed as Rapid Deceleration Zone.
Green This cluster shows gradual deceleration and acceleration close to 0. Node 60 and other nodes where the vehicle was standing most of the time were also present. Hence this cluster can be termed as Bus Stop Zone.
White The velocity in this cluster is average, and the braking and accelerations are random. The vehicle is also not stopping. Hence this cluster shall be termed asStop and Go Zone.
3.2 Manoeuvres and Fuel Consumption
Two particular trips labelled Trip 49 and Trip 53 were considered for the characterization phase. Trips 49 and 53 had a fuel consumption of 16.1 litres and 7.8 litres, respectively, despite having travelled a similar distance of 40km approximately (40.13 km and 40.73km respectively), Trip 49 had more than twice the consumption of Trip 53. The mapping density is plotted in Figs. 10 and 11. The density is log-transformed similar to Fig. 5 due to the domination by node 60.
3.2.1 Trip 49 - High Consumption trip
Out of the 1335 manoeuvres 119 were not mapped to any of the map nodes. This might be because the training set consisted of a limited duration, and when a completely new driver is observed, the manoeuvres can be completely different.
As seen in Fig. 10, all types of manoeuvres (clusters) were observed in this trip. The node 60 had the highest density (number of mappings) with 501 observations mapped to it, similar to the training set. This being a bus stop zone manoeuvre, is an expected action in a city bus.
3.2.2 Trip 53 - Low Consumption trip
Since the trips were having the same time duration, trip 53 also had 1335 manoeuvres observed, out of which 120 were not mapped to any nodes.
It was observed that most of the mappings of trip 53 were also quite similar to trip 49, as seen in Fig. 11. Node 60 was also the highest density node in the trip. In comparison to trip 49, trip 53 had fewer types of Yellow or rapid deceleration manoeuvres present on the top-right of the map.
3.2.3 Trip differences
When observing the fuel consumption of the trips in Figs. 12 and 13, Trip 53 was found to have more fuel consumption in the High-Speed Zone cluster and Bus Stop Zone node. Trip 49 did not have such very high consumption manoeuvres. On the contrary, Trip 53 had less fuel consumption for the total trip.
In order to distinguish the manoeuvres observed in the two trips Fig. 14 was constructed where, 1 indicates that the manoeuvre was exclusive to Trip 49, 2 indicates that the manoeuvre was exclusive to Trip 53, and 3 denotes it common to both trips.
In Fig. 14, nodes 78 and 79 (Yellow node on the right edge, fourth from the bottom of the map in Fig. 14 is node 80. Its neighbours to the left are 78 and 79), are coloured red and orange respectively. These are nodes present in the Bus Stop Zone or Green cluster. Red denotes, it was observed only in Trip 49 and orange was only present in Trip 53.
To investigate the driving manoeuvres better, a pair of similar manoeuvres is taken. The codes of node 78 and 79 are plotted in Figs. 15 and 16, respectively. In node 79, the velocity was initially less than 15 m/s and due to the braking, reduces to approximately 2 m/s. The brake was released at time 2 s and the velocity was constant until time 7 s. To avoid halting, Accelerator Pedal was slightly pressed.
In node 78, the velocity was initially higher at about 24 m/s. Due to the braking, it decelerated to approximately 2 m/s at time 3 s and dropped further until time 5 s. Again the Accelerator Pedal was pressed here, slightly higher than in node 79.
Thus manoeuvre 78 was more aggressive than 79. It can be concluded that the driver of Trip 49 was more aggressive at lower velocity manoeuvres when compared to the driver of Trip 53. This explains the fuel consumption difference to some extent.