TNO Human Factors

Mental load of the Westerschelde tunnel operator

Drs. Jouke RypkemaTNO Human FactorsP.O Box 233769 ZG Soesterberg+31 346 356322rypkema@tm.tno.nl

Mental load of the Westerschelde tunnel operator 2Human Factors

Westerschelde motor-traffic tunnel: location

Mental load of the Westerschelde tunnel operator 3Human Factors

Westerschelde motor-traffic tunnel: details

• 6.6 km long• 2 tubes, each tube 2 driving lanes• Evacuation corridors every 250 m• Cameras every 150 m• 20 monitor displays• Sensors (e.g. traffic speed, vehicle height, sight)• Controllers (e.g. traffic lights, speed reduction signs)• One operator to guard the tunnel

Mental load of the Westerschelde tunnel operator 4Human Factors

Question:

Can the tunnel be controlled safely by one tunnel operator?

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Cognitive load analysis

• Is the operator capable to (cognitively) perform his or

her tasks?

Mental load of the Westerschelde tunnel operator 6Human Factors

3D cognitive load model

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Scenarios

• Five scenarios were analysed• Some severe (for example, accident with bus that

catches fire)• Some more common (for example, car without fuel

standing still in tunnel)

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Scenarios: method analysis

Event

Bus hits car and catches fire,

two lanes blocked

procedurePerform calamity

System(TUBES)

OperatorTime

0

5

5

35

35

Notification (auditory/visual)

Detection on MMI

Autostart ventilation (after 60s)

Press calamity button

1

5

30

0

Auto CCTV selection Build-upinternal image

Mental load of the Westerschelde tunnel operator 9Human Factors

Results

• Time occupied always high (vigilance)• Overall, average cognitive load acceptable, but• Cognitive load is extremely high for three scenarios

during period just after incident

Scenario 1 2 3Time (in sec) 0 - 675 0 - 1105 0 - 920Time occupied (in %) 100 100 100Complexity (in %) 52 54 23Task-set switches(number)

13 12 10

Task-set switches(average time betweenswitches)

52 92 92

Critcal p

eriod

Mental load of the Westerschelde tunnel operator 10Human Factors

Results (2)

Level of information processing

Task-set switches

Time occupied

1

23

4 5

12

3

Mental load of the Westerschelde tunnel operator 11Human Factors

Conclusions

Cognitive load too high at the start of incidents, because:• Too many tasks in short time (especially with evacuation)• Tasks too complex because lack of (clear) procedures• Sometimes number of task-set switches too high as a

result of intertwined task-sets

And:• Sudden change from monotonous vigilance task to

highly demanding crisis situation• Responsibility until emergency services arrive

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Recommendations

• Develop / improve procedures related to categories of

incidents.• Develop evacuation procedures. Pay attention to

communication and guidance.• Improve procedures for communication with third

parties. Restrict communication tasks during crisis

situations.• Cluster the operator tasks in sets.• Provide a second person for assistance during crisis

situations.

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Recommendations training

• Train “on the job” for normal situations.

• Use a simulator to train for critical situations.

• Repeat training frequently (3-6 monthly).

• Organize interdisciplinary training with emergency

services.

Mental load of the Westerschelde tunnel operator 14Human Factors

Thank you for your attention

For more information contact:

Jouke Rypkema

rypkema@tm.tno.nl