The flow brake inlet opening (17) has a size with a minor transverse dimension (ai; si).

A drag device such as a ballute (29) is attached to the rearmost trailing projectile vehicle (21z).

The present invention thus provides a pneumatic deceleration device that has a low dispersion of deceleration forces.

Said speed deterrent is adapted to be able to assume a first inactive position and a second active position.

Furthermore, the handle device (30) may also be provided with an attenuating device (80 (210)) that reduces the retraction speed of the supporting rods.

Said decelerator device (1) is characterised in that it comprises a balancing device (20) incorporated in the gate (2) body (4) and comprising a leakage conduit (21) controlled by a calibrated check valve (22).

A gully (1) comprises a gully side connector(3)at an outlet opening (10), and a flow brake (13) is mounted in said gully (1).

An apertured retarding device (50) is placed on the tape (11) within the container (20) to retard the passage of the tape through the restraining member (12) thus controlling the rate of descent.

The speed deterrent is adapted and intended to be placed against and/or in a road section ('c') intended for the advancement of a vehicle (41), with a view to causing a vehicle driver to reduce the speed of the vehicle along a stretch of road.