**Acknowledgements**

This research was developed under the auspices of the Spanish Ministry of Science and Innovation —who funded the project ASUCAR (PET2008\_0328) in the 2008– 2011 National Research Programme—and the ASUCAR-2 research project *Validation of the usability of a retention system for the safety of children's carriages in public transport vehicles*, funded by the Polytechnic University of Valencia in the INNOVA 2012 Program (Contract No. 20120579). The development of the injury criteria used in this study was supported by the Spanish Ministry of Science and Innovation who funded the project *Children and Elderly Safety in Bus Accidents* (CESBA/SANCA) (TRA2011-26313) in the 2008–2011 National Research Programme.
