Lexus ES300 2003 Manual page 135

The SRS front airbag system is designed to activate in
response to a severe frontal impact within the shaded area
between the arrows in the illustration.
The SRS front airbags will deploy if the severity of the impact
is above the designed threshold level, comparable to an
approximate 25 km/h (15 mph) collision when impacting
straight into a fixed barrier that does not move or deform.
If the severity of the impact is below the above threshold level,
the SRS front airbags may not deploy.
COMFORT ADJUSTMENT
However, this threshold velocity will be considerably higher if
the vehicle strikes an object, such as a parked vehicle or sign
pole, which can move or deform on impact, or if it is involved
in an underride collision (e.g. a collision in which the nose of
the vehicle "underrides", or goes under, the bed of a truck,
etc.).
It is possible that in some collisions at the lower zone of airbag
sensor detection and activation, the SRS airbags and seat belt
pretensioners will not operate all together.
For the safety of all occupants, always wear your seat belts
properly.
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