International Journal of Industrial Ergonomics 35 (2005) 939–953

Situation awareness and workload in driving while using adaptive cruise control and a cell phone

Ruiqi Ma, David B. Kaber

Speaker: Jenny

2008/10/08

Introduction

• Driving tasks: perception, comprehension, projection, decision of action, and implement the action.

• Advanced automation technologies– improve safety, efficiency, and

comfort– increased monitoring workload,

and attention distraction. (Ward, 2000)

Existing theory on SA in driving

• 3 levels of SA: perception, comprehension, and projection. (Endsley, 1995)

• 3 general types of driving tasks: operational, tactical, and strategic.

(Ward, 2000) (Matthews et al., 2001)

• Multiple elements of awareness defining driving SA: spatial, identity, temporal, goal, and system. (Matthews et al., 2001)

Existing theory on SA in driving

• System factors influence operator achievement of SA, including the number and complexity of automation systems. (Endsley, 1995)

• Critical knowledge to SA: navigation, environment and interaction, spatial orientation, and vehicle status knowledge.

Previous studies

• Intelligent transportation system includes ACC.

• Adaptive cruise control (ACC): adjust vehicle speed

• Long headway distance (2.4s):reduce the frequency of “tailgating” and the severity of rear-end collisions, lower driving workload.

• fewer safe brake: ACC may increase the accident from driver distraction, when performing more in-vehicle secondary tasks.

Impact

• Cell phone: driving workload↑, SA↓, task performance↓ .

• Limited mental resources• Worse effect of cell phone

conversation: caller can’t visualize the situation, and driver may use one hand to hold the phone

• hands-free cell phone: increasing the headway distance and decreasing speed to compensate the need for increased action time. (Chen and Lin, 2003)

• Situation Awareness measure:– Location-recall probe– Performance probe– Scene-interpretation probe

1. Investigate the effects of ACC and cell phone use in driving on a direct and objective measure of SA and perceived driver workload

2. Access the competition of multiple driving and communication tasks for limited mental resources

• How to implement in-vehicle automation to facilitate and support driver SA

• How to balance driving and secondary tasks to ensure good SA and performance

Apparatus: medium fidelity driving simulation (C++), stereographic goggles, cell phone (Motorola T720)

Experiment design

• Four 25-min session• 18 college students: 9 males and 9 females• Independent variable

– ACC control mode, cell phone use condition• Dependent variable

– driver SA (3 level: perception, comprehension, projection)

• Simulation freeze technique: SAGAT (situation awareness global assessment technique)

• SA questionnaire: recall car locations and colors, and traffic signs

Method--Task• Changes in speed and lateral position• Maintain car in the right-hand lanes of

the 4-lane freeway• keep car in the middle of a particular

lane• Observe road signs• ACC / no-ACC control modes• User car maximum speed: 80mph (Lead car speed: 60 mph)• Headway distance: 2.4s• Adjust the user car speed relative to

lead car speed changes (1.4s)• Cell phone: 10 arithmetic questions/ call

(last less than 2mins)

• Subjective workload: mental demand rating scale

• Participant accuracy: headway distance (optimal range: 8-25m), following speed, lane tracking and maintenance on the straight and curve lanes

Hypotheses

• ACC system improves driver SA under no unexpected events

• ACC decrease mental workload—driver boredom and vigilance decreases over time without ACC control (Ward, 2000)

• Cell phone use would degrade driver task performance (Hancock et al., 1999,2002)

Results

Results

Result—driver SA

• ANOVA• Tukey Test• In-vehicle automation: reduce

driver task load, and improve driver SA

• Cell phone conversation: degrade driver comprehension and projection of state of the driving environment and overall SA

Results-driving workload

Results-driving performance• Vehicle control is affected

by ACC system, not cell phone conversation.

• Reason: the cell phone conversation is intermittent and didn’t pose a continuous secondary load on drivers.

Results-driving performance• Headway distance

Results-driving performance• Following speed

Results-driving performance• Land maintenance on

curves– There was a trend for greater

lane maintenance deviations on curves when the ACC control was inactive.

• In summary, cell phone conversations during driving wouldn’t decrease task performance. (Since the duration is too short.)

Conclusion

• the importance of interaction with in-vehicle systems to human perception, comprehension, and projection of driving environment states.

• ACC under typical driving conditions could facilitate driver situation awareness.

• Agree with prior work (Parker et al., 2003), this study found improvements in variation in headway distance and following speed control with ACC.

conclusion

• Hand-held cell phone use can be harmful to driver SA. (Gugerty et al, 2003)

• Chen and Lin(2003) showed significant driving performance decrease due to cell phone use, but this study didn’t get the same result.

• Similar to Rudin Brown et al.(2003) results, we found that the benefits of ACC, in terms of workload reduction, were offset by workload increases due to cell phone use.