Actions to improve the use of Child Restraint Systems to prevent displacement "out of position" during the sleep phase

Actions to improve the use of Child Restraint Systems to prevent displacement "out of position" during the sleep phase De Miguel Miranda, Juan Luis 1 ; Olona Solano, Ana Luisa 2 Support for the study was provided by DGT Nº 0100DGT21368 Abstract: It has been proved that children who travel asleep, in a vehicle, have a high risk of their body being displaced to positions in which they would be particularly vulnerable, in the event of an accident. Once they have been observed the most frequent positions adopted by children in a vehicle, during the sleep phase, depending of the kind of Children Restraint System (CRS) used, arises the need for analyzing the effects of children s position and the seat belt position, on the foreseeable injury risk in a crash. This study, based on computer simulation, aims to estimate an injury risk (in different parts of the body) for each collision configuration, depending on the CRS used (highback booster, backless booster and without CRS), depending also of the positions of the child in the vehicle, allowing to assess how the foreseeable injury risk increases if the child is sitting out of position, during the sleep phase, compared with the injury risk if the child is sitting in the correct position. It has been observed that CRS s which allows a correct belt fitment are more effective protecting the occupants in the event of a crash. The use of highback booster provides a better adjustment of the shoulder belt, which greatly decrease the lateral movement of the head. While the use of the P series dummies, currently contained in the standard approval, allows a correct analysis of the movement of the occupants, their limited biofidelility for the analysis of injuries could be the cause of the not very precise results. For this reason it is proposed the use of the Q series dummies, for future research, which are more biofidelic, according to various studies. Keywords: Child Restraint Systems (CRS), Child Safety Transport, out of position, sleep phase, booster, seat belt, injury risk. 1. INTRODUCTION. Different researchers have suggested that the movement "out of position" of the occupants could reduce the effectiveness of the Child Restraint Systems (CRS) [2,4,5]. This problem gets worse when the children use a CRS belonging to the group II and III (using the adult seat belt), as well as on older children that do not use any CRS, especially during the sleep phase, as some observational studies have shown [2]. The overall aim of this project is to quantify, by computer simulation, the injury risk of children who travel asleep in a vehicle, depending on the CRS used and depending on the position of the children, which may suggest guidelines to improve the use of existing CRS as well as to encourage new designs and improved SRI. The target population of the project has been children, of approximate ages between 6 and 14: users of CRS s belonging to the groups II and III (between 15 and 36 kg, and height under 135 cm) and users who are not required to use CRS (height > 135 cm), since it is a high-risk population, because their body has lower physiological tolerance than adults, especially when traveling asleep, as their body is in a more vulnerable position, and using a seat belt designed for adults. simulations to study each case. In particular, it has been done the simulation of the case when the child uses highback booster seat, backless booster seat and none CRS. In the three cases showed it has been analyzed the configuration in which the child was sitting properly and the case in which the child was out of position by being asleep ( out of position 1 (OOP1): Off of the shoulder, the shoulder belt is on the arm instead of being on the acromion; out of position 2 (OOP2): the belt is pressing into or supporting the 6 years old girl in position. Out of Position 1 (OOP1). 2. METHOD. Once analyzed several studies about the position of the children when they fall asleep in the car [1,2,3,4,5,6], it has been performed computer Out of Position 2 (OOP2). Out of Position 3 (OOP3). Of the three cases of out of position analyzed in the study [2], it had been only studied two cases of out of position because 2 and 3 can be grouped into 1 Industrial Engineer, CENTRO ZARAGOZA, Accident Research and Road Safety Area, Spain 2 Industrial Engineer, CENTRO ZARAGOZA, Accident Research and Road Safety Area, Spain

one, to influence both on the support of the shoulder belt on the neck. The software used to perform the computer simulations is MADYMO ((MAthematical DYnamic MOdel), that allow analyze the kinematics and the injury risk of the vehicles occupants. It had been chosen the dummies P6 and P10 to analyze the kinematics and strains to which it is subjected a 6 year old child and a 10 year old child, respectively, in several configurations to be analyzed. P series were developed by TNO for the evaluation of child restraint devices in vehicles. These dummies have been chosen to be used in the SRI approval standard (ECE-R44). On the other hand, to analyze the kinematics and strains to which it is subjected a 12-14 years old young person it is used a HybridIII 5 th dummy, representing a woman who heights 152 cm and weights 50 kg, being the most widely resembles. It had been developed a simplified interior vehicle model in which had been placed the dummies, in order to analyze their kinematics and strains to which they are subjected to each of the configurations under study. In the analyzed simulations it had been used as group II CRS (dummy P6 case) the Cybex Solution X-Fix CRS, equipped with ISOFIX. As group III CRS (dummy P10 case) was used the Cybex Solution X-Fix without back. This CRS was chosen because it obtained the result as "satisfactory" in the analysis of child restraint system 2011 performed by RACE [7]. As for the analyzed solicitation, the study had been focused on three kind of collision: frontal, rear and collision (almost any collision can be conred a combination of the above configurations, and rollover modifies so much previous position of the occupants that the out of position before the vehicle runs out of the road is irrelevant). For each of the case studies it had been to measure different variables that allowed determining the injury risk in different areas of the body. capable of being analyzed in real crash tests with dummies and physical CRS. This crash tests were performed by TESSA (Technologies and Systems for Automotive Safety), University of Zaragoza, unrelated to this project. These results were contrasted with the simulations carried out, in order to estimate the error thereof. The performed crash tests were frontal collision with P6 dummy and frontal collision with dummy P10. Figure 2. Comparison between frames of the crash test frontal collision with dummy P6 and frames of the simulation carried out whith MADYMO. Performing a critical analysis of the resultant thorax acceleration and Z thorax acceleration, and the excursion of the head in the case of P6 dummy, it is observed that the simulated model results in a decrease of 19.5, an increase of 9.4 and a decrease of 8.5, respectively. Performing the same analysis in the case of the P10 dummy, it had obtained a decrease of 1.9, an increase of 15.9 and a decrease of 22, respectively. It was concluded that the model made with MADYMO is very close to the real model. Figure 1. Child Restraint System Cybex Solution X- Fix used as group II (left). In the right this model used in MADYMO. As external quality control it had selected two cases, of the array of 27 cases to be simulated, which are Figura 3. Comparison between frames of the crash test frontal collision with dummy P10 and frames of the simulation carried out whith MADYMO. 2

3. RESULTS. This section shows the results obtained in each of the cases analyzed with MADYMO, specifying for each collision configurations studied. 3.1.- FRONTAL COLLISION To reproduce the frontal collision, it has been introduce a acceleration pulse in the model made with MADYMO, this pulse is within the corridor indicating by the standard ECE R-44. Figure3. Acceleration pulse introduced in the frontal collision. 3.1.1- FRONTAL COLLISION: DUMMY P6. Cybex Solution X-Fix, when the vehicle in which figure 3. For this configuration of collision it has been studied five different cases: dummy in position, dummy out of position OOP1 (Off of the shoulder, the shoulder belt is on the arm instead of being on the acromion), dummy out of position OOP12 (as dummy OOP1 but more inclining to the left), dummy out of position OOP2 (the belt is pressing into or supporting the neck) and dummy out of position OOP21 (as dummy OOP2 but with the belt most supporting the neck) The table 1 shows the values obtained for the different controlled variables. It can be observed that the head acceleration decreases more than 15% in the case of out of position OOP2, this may be because the head is resting on the of the backrest and is also bended forward. In all cases of out of position the value of HIC (Head Injury Criterion) is less than for the case in position, this may be because the head is resting on the of the CRS. In position DUMMY P6, FRONTAL COLLISION OOP1 % OOP12 % OOP2 % OPP21 % Head_acc 501,97 460,09-8,3 465,51-7,3 422,61-15,8 417,13-16,9 Thorax_acc 325,37 327,24 0,6 320,21-1,6 335,94 3,2 342,99 5,41 Pelvis_acc 336,74 319,73-5,0 300,07-10,8 330,19-2,0 358,99 6,6 Force on neck (N) 1958,4 1577,8-19,4 1533,5-21,7 2032 4,0 2000,4 2,1 Moments in neck 19,83 17,84-10,0 17,57-11,4 19,66-0,8 18,83-0,1 HIC (16 ms) 228,67 199,17-12,9 179,43-21,5 164,91-28,0 152,79-33,2 HIC (36 ms) 379,24 347,93-8,2 329,45-13,1 288,95-24,0 276,20-27,2 CONTIGUOUS 284,96 267,98-5,9 255,33-10,4 299,68 5,2 319,87 12,3 CUMULATIVE 303,09 297,90-1,7 282,99-6,6 311,52 3,0 328,28 8,3 Table1. Results obtained in the simulation of a frontal collision (dummy P6). The forces on the neck decrease around 21% in the out of position OOP1, according as the dummy is more inclined to the left, according to the direction of travel of the vehicle, the force on the neck decreases. In the case of out of position OOP2 (belt on the neck belt) the forces increased but slightly, this is because with the dummy P6 could not measure the injury risk due to the belt support on the soft tissues by compression. If we analyze the moments in the neck, it is concluded that the more separated dummy's neck from the shoulder belt, the moment is smaller. Analyzing the kinematic it has been seen that the head is inclined more towards the right and forward (OOP21) according to the direction of travel of the vehicle, the excursion of the head is higher. 3.1.2- FRONTAL COLLISION: DUMMY P10. Cybex Solution X-Fix without back, when the vehicle in which travels, experiments the pulse acceleration shown in figure 3. For this configuration of collision it has been studied the same five different cases analyzed in the case of frontal collision with the dummy P6. The head acceleration decreases when the dummy head is out of position, it may be because in these cases the dummy head is more advanced than in the case that the dummy is in place. In the case of the forces on the neck, it is concluded that according as the dummy is more inclined to the left, according to the direction of travel, the force on the neck decreases. In position DUMMY P10, FRONTAL COLLISION OOP1 % OOP12 % OOP2 % OOP21 % Head_acc 641,51 584,58-8,8 511,40-20,3 522,43-18,6 487,67-24,0 Thorax_acc 529,77 401,88-24,1 441,17-16,7 469,82-11,3 429,07-19,0 Pelvis_acc 553,18 594,85 7,5 703,73 27,2 416,08-24,8 512,34-7,4 Force on neck N 2992,1 2596,6-13,2 2519,9-15,8 2956,3-1,2 2797,0-6,5 Moment in neck Nm 38,30 38,66 0,9 37,93-0,9 21,34-44,3 18,90-50,6 HIC (16 ms) 494,44 413,59-16,4 389,02-21,3 328,37-33,6 328,31-33,6 HIC (36 ms) 332,91 262,11-21,3 225,58-32,2 167,62-49,6 180,71-45,7 CONTIGUOUS 352,82 279,53-21,0 269,30-23,7 366,53 3,9 355,98 0,9 CUMULATIVE 449,53 366,98-18,4 391,15-13,0 423,51-5,7 381,08-15,2 Table2. Results obtained in the simulation of a frontal collision (dummy P10). 3

If it has been analyzed the moments in the neck is concluded that in the case of the backless booster when the dummy neck was closer to the shoulder belt, the moment in the neck is smaller, this trend is contrary to what happened with the dummy P6. This may be because the dummy P6 is placed in the rear seat right while the dummy P10 is placed in the rear left seat. Analyzing the kinematic it has been concluded that the excursion of the dummy head when the dummy is in position is higher than when the dummies are out of position (OOP1 and OOP2), while for the case of out of position OOP2 and OOP21, the excursion of the dummy head is smaller than for the case in which the dummy is in place. 3.1.3- FRONTAL COLLISION: DUMMY HybridIII 5 th. which a dummy HybridIII 5th is subjected, using the adult belt safety, as he measure over 135 cm and can travel without CRS, when the vehicle in which figure 3. For this configuration of collision it has been studied three different cases: dummy in position, dummy out of position OOP1 (Off of the shoulder, the shoulder belt is on the arm instead of being on the acromion), and dummy out of position OOP2 (the belt is pressing into or supporting the DUMMY HYBRIDIII 5 th, FRONTAL COLLISION Head_acc 637,97 676,74 6,0 639,24 0,2 Thorax_acc 333,53 343,06 2,8 346,38 3,8 Pelvis_acc 344,74 346,91 0,6 350,83 1,8 Force in Neck N 2189,3 2134,3-2,5 2112,1-3,5 Moment in Neck Nm 40,30 55,64 38,0 56,05 39,1 HIC (16 ms) 451,26 528,05 17,0 470,08 4,2 HIC (36 ms) 692,37 791,53 25,7 673,30-2,7 NIC FORWARD Neck axial force (N) 1775,3 1789,7 0,8 1659,1-6,5 Fore/aft neck shear force(n) Neck bending moment 175,8-1335,3 126,5-1261,9-28,0-5,5 64,88-1306,6-63,1-2,1 60,5 74,6 23,3 73,74 22,0 NTF 0,755 0.8079 7,0 0,8165 8,1 NTE 0,3251 0.43 32,3 0,278-14,5 NCE 0,537 0.4559-15,1 0,5079-5,4 NCF 0,0138 0.0086-37,7 0,01522 10,3 Table3. Results obtained in the simulation of a frontal collision (dummy HybridIII 5 th ). Relating to the moment in the neck is concluded that in the case of this dummy, so if it has the shoulder belt on the arm as if it has the shoulder band on the neck, the moment that the neck experienced is higher than if the dummy is in position. Furthermore, in the three cases, the sum of all indicators Nij is higher than 1. Obtaining the highest value in the case in which the dummy is out of position OOP1. Finally, as regards the kinematics is concluded that in the configuration of OOP1 the excursion of the head is higher than in the remaining positions. 3.2.- REAR COLLISION. To reproduce the rear collision, it has been introduce a acceleration pulse in the model made with MADYMO, this pulse is within the corridor indicating by the standard ECE R-44. Figure4. Acceleration pulse introduced in the rear collision. 3.2.1- REAR-END COLLISION: DUMMY P6. Cybex Solution X-Fix, when the vehicle in which figure 4. For this configuration of collision it has been studied three different cases: dummy in position, dummy out of position OOP1 (Off of the shoulder, the shoulder belt is on the arm instead of being on the acromion), and dummy out of position OOP2 (the belt is pressing into or supporting the From the table 4 it has been concluded that the head acceleration, in the case of out of position OOP2, increased by 87.2% compared to the head acceleration in the case that the dummy is in position. This increase may be due to the dummy's head in this out of position is more forwardly inclined than the rest of configurations, making impact against the SRI later and with higher acceleration. On the other hand, in this case out of position the forces on the neck are increased by 97.4% and the moments in the neck are increased by 65.5% compared to the reference case. As in the case of acceleration, this increase may be due to the dummy's head in this out of position position out is more inclined forward. DUMMY P6, REAR-END COLLISION Head_acc (m/s2) 276,25 264,54-4,2 517,27 87,2 Thorax_acc 300,89 305,05 1,4 266,82-11,3 Pelvis_acc 309,12 314,16 1,6 313,69 1,5 Force on neck N 225,06 200,3-11,0 444,27 97,4 Moment in neck Nm 4,47 4,86 8,7 7,40 65,5 HIC 40,171 41,332 2,8 144,42 259,5 CONTIGUOUS 293,63 294,48 0,3 258,22-12,1 CUMULATIVE 293,72 295,06 0,5 259,51-11,6 4

Table4. Results obtained in the simulation of a rear collision (dummy P6). DUMMY HYBRIDIII 5TH, REAR-END COLLISION Head_acc 379,85 296,93-21,8 203,19-46,5 Thorax_acc 221,02 188,82-14,6 202,93-8,2 Pelvis_acc 336,23 316,48-5,9 332,47-1,1 3.2.2- REAR-END COLLISION: DUMMY P10. which a dummy P10 is subjected, in a rear collision with the acceleration pulse shown in the figure 3. When the vehicle in which travels, experiments the pulse acceleration shown in figure 3. For this configuration of collision it has been studied the same cases analyzed in the before case: in position, OOP1 and OOP2. It can be seen in the following table that the out of position in this case doesn t affect greatly in the injury risk or in the dummy kinematics, this may be because the P series dummies have not been validated for rear collision and its biofidelity is limited. DUMMY P10, REAR-END COLLISION Head_acc (m/s2) 284,69 309,60 8,7 351,34-4,2 Thorax_acc (m/s2) 287,14 284,82-0,8 289,15 1,4 Pelvis_acc (m/s2) 252,53 307,46 21,7 259,23 2,6 Forces on neck N 557,95 545,73-2,2 549,22-1,6 Moments in neck Nm 8,166 9,173 12,3 9,8 13,1 HIC 42,274 50,249 18,8 66,089 56,3 Force on neck N 724,85 671,31-7,4 796,58 9,9 Moment in neck Nm 30,57 31,93 4,4 29,93-2,1 HIC 81,952 51,973-36,6 46,038-43,8 NIC FORWARD Neck axial force (N) 337,1 247,5-26,6 201,9-40,1 Fore/aft neck shear force(n) Neck bending moment 173,5-96,6 143,0-124,1-17,6 28,5 115,7-161,9-33,3 67,6 9,41 6,2-34,1 4,9-47,9 NTF 0,068 0,0351-48,4 0,052-23,5 NTE 0,121 0,1171-3,2 0,084-30,6 NCE 0,6096 0,6055-0,7 0,592-2,9 NCF 0,0688 0,0458-33,4 0,035-49,1 Table6. Results obtained in the simulation of a rearend collision (dummy HybridIII 5 th ). 3.2.- SIDE COLLISION. To reproduce the collision, it has been introduce a acceleration pulse in the model made with MADYMO, the following acceleration pulses corresponding to a collision of medium-high severity, it has been difference between whether the impact is produced on the right of the vehicle by way or if the impact has occurred on the left CONTGUOUS 280,14 279,87-0,1 284,13 1,4 CUMULATIVE 280,24 280,13-0,04 284,32 1,5 Table5. Results obtained in the simulation of a reaendr collision (dummy P10). 3.2.3- REAR-END COLLISION: DUMMY HybridIII 5 th. In this case it has been analyzed the kinematics and strains to which a dummy HybridIII 5th is subjected in the analyzed rear-end collision. For this configuration of collision it has been also studied the same cases that have been analyzed in the previous two sections: in position, OOP1 and OOP2. The head acceleration is reduced by 21.8% in the case of OOP1 and by 46.5% in the case of OOP2 with respect to the case in which the dummy is in position. Analyzing the kinematic and head acceleration graphs, it has been seen that the head of the dummy in this position is forward with respect to the out of position, this fact made that in the rear-end collision the head impacts later against the headrest and experiences higher acceleration. If we study the forces and moments in the neck can be seen as decrease when the dummy is out of position, however the negative shear (backward) is increased. The dummy Hybrid III 5 th, being more biofiel than the P series, isn t designed to analyze rear-end collisions, for this it has been developed the dummy Biorid2. Figure5. Acceleration pulse collision (impact right ). Figure6. Acceleration pulse collision (impact left ). It should be noted that to date the ECE-R44 does not include any requirement with regard to the lateral protection to be met by CRS and therefore, no sets the lateral acceleration pulse to which shall be tested. 3.3.1- SIDE COLLISION: DUMMY P6. Cybex Solution X-Fix, when the vehicle in which figure 5 (impact right ) and when experiments the acceleration pulse shown in the figure 6 (impact left ). For this configuration of collision it has been studied three different cases: dummy in position, dummy out of position OOP1 (Off of the shoulder, the shoulder belt is on the arm instead of being on the acromion), and dummy out of position OOP2 (the belt is pressing into or supporting the 5

For the case of out of position OOP1 (dummy more inclined to the left, if the impact is on the right, the solicitations to which the dummy is subjected increases conrably compared to the reference case. On the other hand, if the impact is received on the left the trend reverses, reducing such solicitations. In the case of out of position OOP2 it has been seen that the trend is reversed, ie, in case of receiving an impact on the right, the solicitations decreased with respect to the reference case and when the impact is on the left, they conrably increase. This is because the proximity to the place from which the impact come. Head_acc Thorax_acc Pelvis_acc Forces on neck N Moments in neck Nm DUMMY P6, SIDE COLLISION In position OOP1 OOP2 Left % Left % % Left % 525,78 620,48 780,88 48,5 231,62-62,7 199,98-61,9 793,59 19,2 413,70 479,31 617,30 49,2 296,09-38,2 328,39-20,6 574,06 19,7 518,77 580,21 602,36 16,1 503,67-13,2 455,31-12,2 564,28-2,7 657,12 861,19 1018,1 54,9 531,73-38,2 534,23-18,7 880,52 2,2 16,98 19,78 18,01 6,1 20,071 1,5 21,98 29,4 22,14 11,9 HIC 120,90 161,23 266,50 120,4 62,085-61,5 41,116-66,0 329,38 104,3 CONTIGUOUS CUMULATIVE 400,21 463,89 596,49 49,1 258,69-44,2 302,95-24,3 556,67 20,0 400,58 466,80 599,96 49,7 268,20-42,5 305,27-23,8 559,31 19,8 Table7. Results obtained in the simulation of a collision (in the right or in the left ) for the case of the dummy P6. 3.3.2- SIDE COLLISION: DUMMY P10. In this case it has been analyzed the kinematics and strains to which a dummy P10 is subjected, when the vehicle in which travels, experiments a impact with the pulse acceleration shown in figure 5 or in the figure 6 ( as the impact on the right or on the left ) The positions that have been analyzed are: in position,oop1 and OOP1. If we analyze the data in the table below, it can see that in this case the trend is reversed with respect to the case of dummy P6, this is due initially to the position of the dummy of reference is different and therefore their out of position. The dummy P6 is placed in the right rear seat, according to the direction of travel of the vehicle, while the P10 dummy was placed in the left seat. Consequently, the shoulder belt is supported on the right shoulder and in the other case on the left shoulder. DUMMY P10, SIDE COLLISION In position OOP1 OOP2 Left % Left % % Left % Head_acc 495,83 2942,1 472,99-4,6 3459,0 17,6 625,17 26,1 1938,2-34,1 Thorax_acc Pelvis_acc Forces on neck N Moments in neck Nm 407,83 1526,4 293,03-28,1 1640,4 7,5 641,79 57,4 1331,8-12,7 577,88 788,62 308,79-46,6 1485,9 88,4 734,65 27,1 613,32-22,2 1569,5 2049,1 1507,2-3,9 2932,4 43,1 1947,1 24,0 1537,7-24,9 63,87 90,56 61,38-3,9 99,48 9,8 60,17-5,8 80,296-11,3 HIC 455,02 7171,0 345,48-24,1 10443 45,6 646,77 42,1 2710,0-62,2 CONTIGUOUS CUMULATIVE 331,50 1343,9 243,15-26,6 1433,8 6,7 471,99 42,4 1175,2-12,5 355,48 1345,1 268,96-24,3 1449,7 7,7 516,55 45,3 1178,6-12,4 Table8. Results obtained in the simulation of a collision (in the right or in the left ) for the case of the dummy P10. 3.3.3- SIDE COLLISION: DUMMY HybridIII 5 th. Finally, it have been analyzed the kinematics and the strains to which it is subjected the dummy HybridIII 5th when the vehicle in which travels experiments the pulse acceleration shown in figure 5 (impact right ). The positions that have been analyzed are: in position and OOP2 OOP1. DUMMY HYBRID III 5TH, SIDE COLLISION En posición OOP1 % OOP2 % Head_acc (m/s2) 2992,1 3623,8 21,1 3039,3 1,6 Thorax_acc (m/s2) 1490,5 2161,0 45,0 1342,2-9,9 Pelvis_acc (m/s2) 1410,06 1580,2 12,1 663,69-52,9 Forces on neck N 4870,8 6570,3 35,0 3014,7-38,8 Moments in neck Nm 84,18 144,48 71,6 100,71 19,6 HIC 4220,9 6978 65,3 4066,6-3,6 NIC FORWARD Neck axial force (N) 3246,5 3212,8-1,0 2631,2-18,9 Fore/aft neck shear force(n) Neck bending moment 1105,2-876,1 1668,7-842,11 50,9-3,8 335,5-662,06-69,6-24,4 18,6 10,8-41,9 36,1 94,0 NTE 0,9923 1,0033 1,1 0,7979-19,6 NTF 0,0997 0,084-15,7 0,06342-36,4 NCE 1,636 1,874 14,5 0,723-55,8 NCF 0,2273 0,1837-19,2 0,313 37,7 Tabla9. Results obtained in the simulation of a colision (in the right ) for the case of the dummy HybridIII 5 th. In the case of the out of position OOP1 (dummy more inclined to the left) if the impact is on the right, the solicitations to which the dummy is subjected increases conrably compared to the reference case, being the moment in the neck that experienced the greatest variation. Regarding the case of out of position OOP2 it can seen that the trend is reversed, ie, if the vehicle received the impact in the right the solicitations decrease compared to the reference case. 4. DISCUSSION. While the results keep consistency with the kinematics, are not as expected in the case of a frontal collision, rear-end collision and collision, by using the dummies P6 and P10. This is because these dummies allow to analyze the kinematics but their biofidelity for injury analysis 6

and prediction is limited. These dummies allow measurements of head acceleration, force and moment in the neck, but the injury risk may be increased due to the support of belt over soft tissues by compression, an aspect that can not be measured with these dummies. The choice of these dummies was made to be the currently contained in the standard approval CRS's, but future research should use more biofidellic dummies, such as the series Q dummies or six years dummy HybridIII, for the case of frontal collision. On the other hand, has also been taken into account in the analysis that the P series dummies are only validated for frontal impact, except P6, which has also been validated for impact. None has been validated for rear-end collision. The same happens for the case of dummy HybridIII 5th percentile, which is validated only for frontal impacts. The rear-end collision could have been analyzed using the dummy BioridII and the impact using the dummy Eurosid, but models of these dummies are available only for adults. 5. CONCLUSIONS. The CRS design influences on the results, since it has a great influence on the fixing of the belt, in particular the guides of the shoulder and lap belt. It is concluded that the use of highback booster seat allows a better adjustment of the shoulder belt and also significantly reduces the lateral movement of the head, which promotes the maintenance "in position" also during the sleep phase. The P series dummies allow measurements of head acceleration and forces and moments in the neck, but the injury risk that may result from the support belt on the soft tissues, by compression, can not be estimated with these dummies. It is appreciated therefore that although the P series dummies allow to analyze the kinematic, its biofidelity for analysis of injury is limited. In the present study it has been used the P series because it is the currently contained in the standard approval CRS's, but for future research it might be more appropriate the use of dummies Q series, more biofidelic according to various studies [8]. children s performance during buckling up. 52nd AAAM Annual Conference Annals of Advances in Automotive Medicine, Octubre 2008. [2] Jason L. Forman, Maria Seguí-Gomez, Joseph H. Ash, Francisco J. Lopez-Valdes, Child Posture and Shoulder Belt Fit During Extended Night-Time Travelling: An In-Transit Observational Study. 55th AAAM Annual Conference Annals of Advances in Automotive Medicina, October 3-5 2011. [3] Kristy B. Arbogast, Michael J. Kallan, Dennis R. Durbin. Effectiveness of high back and backless belt-positioning booster seats in impact crashes. 49th AAAM Annual Conference Annals of Advances in Automotive Medicina, September 12-14, 2005. [4] Marianne Andersson, Katarina Bohman, Anna- Lisa Osvalder, Effect of booster seat design on children s choice of seating positions during naturalistic riding. [5] Matthew P. Read, Sheila M. Ebert-Hamilton, Kathleen D. Klinich, Miriam A. Manary, Jonathan D. Rupp, Effects of vehicle seat and belt geometry on belt fit for children with and without belt positioning booster seats Accident Analysis and Prevention Mayo 2012. [6] Mathew P.Reed, Sheila M. Ebert, Christopher P. Sherwood, Kathleen D. Klinich, Miriam A. Manary, Evaluation of static belt fit provide by belt positioning booster seats. Accident Analysis and Prevention Febrero 2009. [7] RACE. Análisis de los sistemas de retención infantil 2011. Informe 2ª parte. [8] EEVC Report Advanced Child Dummies and Injury Criteria for Frontal Impact. Documento Nº 514. Abril 2008. ACKNOWLEDGEMENTS The project Actions to improve the use of Child Restraint Systems to prevent displacement "out of position" during the sleep phase, file number 0100DGT21368, has been funded by the General Directorate for Road Traffic (DGT), Ministry of the Interior, Spanish Government. 7. REFERENCES [1] Anna-Lisa Osvalder, Katarina Bohman, Misuse of booster cushions An observation study of 7