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The US National Highway Traffic Safety Administration (NHTSA) have developed a test which can indicate that a driver may be under the influence of alcohol.

The NHTSA claim that when performed correctly by trained officers the Standardised Field Sobriety Test (SFST) is reliable in identifying subjects who may be driving under the influence of alcohol.

We outline a simplified version of this three stage test below:

There are two stages in the walk-and-turn test:

Instruction stage:
	Remove any high heels. Stand on a line with the feet in the heel-to-toe position (left foot in front of right) keep arms at sides Listen to instructions and do not begin until being told to do so.

Walking stage:
	Take nine steps, heel-to-toe, along a straight designated line while counting the steps out loud and watching the feet, and then turn and return in the same manner.

Score out of the 8 following signs. (Total score 8)
	During the Instruction Stage
	1. loses balance during the instructions (by breaking away from the heel-to-toe stance) 2. starts walking before the instructions are finished

During the Walking Stage

3. stops while walking to steady self
4. does not touch heel-to-toe
5. steps off the line
6. uses arms for balance
7. loses balance or turns improperly
8. takes the wrong number of steps

* A score of 2 or more suggests that the subject may be above US drink drive limits.

Officers test for an involuntary jerking of the eyeballs as they gaze from side to side. When a person is impaired by alcohol, the jerking of the eyeballs is magnified.
	Hold a pen 12-15 inches in front of the subject's nose with the tip slightly above the eyes Move the pen back and forth (horizontally). The suspect holding their head still must follow the pen with their eyes.

Score each eye for the following three signs. (Total Score 6)

1. the eye cannot follow the pen smoothly (like a marble being rolled across a piece of sandpaper as opposed to across a glass surface)
2. jerking of the eyeball when the eye has moved horizontally as far as it can go
3. jerking of the eyeball begins before the eye has moved 45 degrees , i.e. past the subjects shoulderblade

* A score of 4 or more suggests that the subject may be above US drink drive limits

Stand with feet together, arms at sides
Stand with one foot six inches off the ground, toes pointed out, and count aloud in thousands
(One thousand-one, one thousand-two, etc.) while looking at the elevated foot until told to put the foot down
Do not hop or sway and do not use arms for balance.

Score out of the 4 following signs (Total Score 4)

1. swaying while balancing
2.using arms to balance
3.hopping to maintain balance
4.hopping to maintain balance

* A score of 2 or more suggests that the subject may be above US drink drive limits

DISCLAIMER: This is a simplified representation of the skilled, rigorous and complicated SFST procedure which requires specialist training to achieve accuracy and consistency.

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