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Microsleep causes accidents

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Two recent accident reports have highlighted the dangers of ‘microsleep’ in the railway environment.

The website Tuck.com, which claims it has the largest collection of aggregated data on sleep on the web, says that microsleeps are “brief, unintended episodes of loss of attention associated with events such as a blank stare, head snapping, and prolonged eye closure which may occur when a person is fatigued but trying to stay awake to perform a monotonous task like driving a car or watching a computer screen.

“Microsleep episodes last from a fraction of a second to two minutes, and often the person is not aware that a microsleep has occurred. In fact, microsleeps often occur when a person’s eyes are open. While in a microsleep, a person fails to respond to outside information. A person will not see a red signal light or notice that the road has taken a curve, which is why this phenomenon is of particular interest to people who study drowsy driving. Similarly, during a microsleep, a pilot might not be aware of flashing alarm lights in the cockpit.”

Now the problem has come to a head in two recent reports by the Rail Accident Investigation Branch (RAIB).

The first was on a passenger train which collided with the buffer stops at King’s Cross station last August. The safety digest stated that four passengers and one member of staff reported minor injuries as a result of the accident, and there was minor damage to the train and the buffer stops, which were pushed back by over one metre. A brief brake application was made as the train came into the platform, and then a nine second gap before the emergency brake was applied. The train hit the buffers at around 4mph.

RAIB concluded that the accident occurred because the driver was suffering from fatigue and apparently experienced a microsleep in the last few seconds of the approach to the buffer stops. The driver reported being aware of passing the TPWS sensor but then briefly closed her eyes because they felt tired and were stinging. When she opened them, she was close to the buffer stops and, although she made an emergency brake application, it was too late to avoid a collision.

On 9 November 2016, an early morning Croydon tram service derailed when it hit the 20km/h bend at 73km/h. In addition to the seven fatalities, 61 passengers were injured in the incident, 19 seriously.

The report concluded that the driver probably “lost awareness” prior to the derailment and then became confused about his location. The RAIB believes the incident was linked to fatigue, although not as a result of the driver’s shift pattern, and could have been caused by a microsleep.

The RAIB has recommended that the operator, Tram Operations Ltd (TOL), look into technology that can monitor driver alertness and automatically apply the brakes if a tram is going too fast – neither of which were available at the time.

However, drivers’ union ASLEF called a strike on two separate days as the operator attempted to do just that. The union’s press release stated: “This is because the company has put into tram cabs a device that shines infra-red light beams into drivers faces, and has insisted on operating this system despite the numerous health and safety concerns of our members. Drivers have reported symptoms from headaches and dry eyes to blurred vision and potentially serious eye damage as a result of exposure to this device.”

The strikes never happened, and TfL released a statement stating that the Driver Protection Device uses advanced sensors that track eyelid closures and head movements to detect fatigue and distraction. When fatigue or distraction is detected, an in-cab alarm is sounded and the driver’s seat vibrates to refocus the driver’s attention.

Manufactured by Seeing Machines in Australia, the Driver Protection Device is not a CCTV camera recording a driver’s every move. In the event that fatigue or distraction is detected and the alarm activated, the system will record the three seconds prior to the alarm to enable the incident to be investigated.

The underlying Seeing Machines technology is based on patented eye-tracking and analytics that detects driver distraction and fatigue while on the job. The company signed an agreement with Electro-Motive Diesel, manufacturer of Class 66 locomotives for the UK, to develop the technology for use in rail vehicles.

The technology has a proven track record in the road haulage industry and has been fully safety tested and certified. The system has been independently certified and is safe for indefinite/continuous use. Small amounts of infrared light are used to allow the sensor to see the drivers’ eyes and face in the dark (less than 2 per cent of the level in normal sunlight).

Read more: A short story of a railway and its river




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