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The majority of fatal accidents involve a roll-over of a tractor without a protective structure (ROPS). On July 18th, 1997 a royal Spanish decree was signed to force the installation of a safety cab in all tractors. However, both in Spain and the other European Union (EU) countries, there is still a high number of tractors without an adequate structure to protect the driver from a roll-over. Directive 2003/37/EEC establishes that tractors over 800kg weight have to be homologated by CODE 4. A protective structure that is cheap, easy to build and adaptable to any tractor model lacking ROPS was designed and a model has been developed to evaluate the ROPS according to the Organisation for Economic Co-operation and Development (OECD) code (CODE 4). The model calculates the maximum forces during the tests and the maximum moments in the critical section of the ROPS beams and the attachment moments; and is able to determine the needed steel section of the structure tube, the minimum height of the beams to make rigid the lower part of the structure, and the number, quality and shank diameter of the attachment screws of the ROPS. Owing to the complexity of the calculations a computer program ‘ESTREMA’ was developed A designed, calculated and manufactured ROPS, mounted on a Massey Ferguson 178 tractor, was able to pass the homologation tests without failing on any of the acceptance conditions, which means that the calculation method worked correctly. [Copyright &y& Elsevier]