Double Lane Change Experiment

In this experiment, two groups of drivers participated, one group of two professional tire test drivers and one group of six nonprofessional, but highly skilled drivers, but not familiar with tire testing.

The task demand for the drivers was to drive a double lane change (Fig. 40). The maneuver was driven with a predefined speed kept by the cruise control. The offset between the lanes was set to 5.5 m, instead of the 3.5 m prescribed in the ISO double lane change (ISO, 1999), to make the maneuver more challenging for the drivers without having to drive with very high speed. Unfortunately, due to the track humidity during the available test period for the professional drivers group, the lane change offset had to be set back to 3.5 m for safety reasons.

Figure 40. The double lane change maneuver with the dimensions and cones numbers (Oort, van, 2012). 2 4 6 8 10 12 14 16 18 20 1 3 5 7 9 11 13 15 17 19 0.0 7.5 15.0 45.0 53.3 61.7 70.0 95.0 110.0 125.0 prof: 3.50 nonprof: 5.50 prof: 2.93 nonprof: 2.43 prof: 3.41 nonprof: 5.59 2.25 Y X all units in m = cone

= professional driver group = nonprofessional driv er group

prof: 3.12

nonprof: 2.62

prof nonprof

To influence the task demand, the difficulty of performing the double lane change was adjusted by changing the independent variables speed (low and high speed) and tire (tire 2, 5 and 6). By adjusting these independent variables, the drivers are assumed to act in the task related effort region A3. All these assumptions are validated in section 5.3.

The tests were driven in test clusters, a test cluster being a combination of driver, tire and speed performing consecutive double lane changes. In every test cluster the maneuvers were repeated two (nonprofessional drivers group and afternoon of professional drivers group) to three (morning of professional drivers group) times and this was repeated with and without secondary task, giving 4-6 double lane changes in one test cluster. After each test cluster, the driver scored the experienced mental and physical workload. Each test cluster driven in the morning was also repeated in the afternoon. The order of testing a tire, driving with or without secondary task, the order of driving the speed, all these conditions were counterbalanced as much as possible, to reduce possible order effects. This resulted in data of 360 usable maneuvers, of which 120 were driven by the professional drivers and 240 by the nonprofessional drivers, evenly distributed over speed, tire and with/without secondary task.

Low and High Speed Values

As explained in section 2.4.4, the positioning of the performance and mental workload curves on the task demand axis is subjective. It depends on the difficulty of the task, which depends not only on the task complexity, but also on the driver. Therefore, the values for the low and high speed demands, given as setpoint to the cruise control, were determined separately for the drivers groups and for the morning/afternoon due to possible different circumstances. The speed values were determined so that the high speed value was the speed for which the drivers in that group were just able to drive the maneuver with the less handling tire 2, without hitting any cones. This assured that the high speed demand was near to the border between regions ܣ͵ and ܤ (Fig. 34). A slightly higher speed resulted in decrease of performance, cones were hit, indicating entering region ܤ. Drivers were therefore required to invest much effort for keeping the performance high (no cones hit), resulting in a high driver mental workload. The low speed value was then chosen in a way, so that driving the lane change without hitting any cones was less demanding for the drivers, but still challenging, requiring more mental workload than considered low, which would indicate the left border of region ܣ͵.

The actual values for high and low speed were chosen specific for both groups, because the groups differed in skill level and track. The change in track humidity between the morning and the afternoon of the professional drivers test day also caused a difference in the values for high and low speed. For all low speed values, the value was found 10 km/h lower than the corresponding high speed value. Table 5 shows the values of high and low speed for the two drivers groups.

Table 5. Low and high speed values driven during maneuvers.

Group Maneuvers Low speed (km/h) High speed (km/h)

Professional drivers First half 90 100

Second half 100 110

Nonprofessional drivers All 80 90

Tire Influence on Task Demand

From the subjective evaluations of the professional drivers (described in section 4.6) the average value for the overall judgment of handling evaluation of the three tires used in this experiment are given in Table 6. It should be noted that tire 2, a winter tire, was tested in a different batch than tires 5 and 6, both high performance summer tires, which implies that comparison of absolute scores is not completely correct, but it can give a good indication (for more information, see section 4.6). In general, high performance summer tires, being especially designed for good handling, can be expected to be better handling tires than winter tires.

Table 6. Average value of the overall handling judgment of the professional drivers group.

Tire 2 5 6

Overall Judgment Mean 6.75 7.25 7.75

Tire 2 as the less good handling tire, is assumed to impose a higher demand on the drivers compared to the summer tires. For 6 as the best handling tire, the imposed demand is expected to be lower. If the driver acts in the task related effort region ܣ͵ a higher demand is accompanied with a higher workload.

5. Validation of Assumptions Field