[pawn]public OnPlayerKeyStateChange(playerid, newkeys, oldkeys)
{
    if(newkeys & KEY_CROUCH)
    {
         new Float:x, Float:y, Float:z;
         GetVehicleVelocity(GetPlayerVehicleID(playerid), x, y, z);
         SetVehicleVelocity(GetPlayerVehicleID(playerid), x, y, z + 0.3);
    }
    return 1;
}[/pawn]