In Portugal tricycles with an "outer" structure or safety structure and seat belts do not require the use of helmets. Here the "google translation" to English, with a few "add ons" by me, of #3 and #4 of article 82 from our "Código da Estrada" (Road Code I guess)

3 - Drivers and passengers of mopeds, motorcycles with or without sidecar, tricycles and quadricycles, must protect the head using officially approved type of helmet, properly adjusted and tight.
4 - Exempt from the provisions of the preceding paragraph are the drivers and passangers of vehicles with a rigid outer closed structure or vehicles with both rigid protective structure and seat belts.

Here the original, in case anyone wants to learn portuguese laugh2

Quote:

3 - Os condutores e passageiros de ciclomotores, motociclos com ou sem carro lateral, triciclos e quadriciclos, devem proteger a cabeça usando capacete de modelo oficialmente aprovado, devidamente ajustado e apertado.
4 - Excetuam-se do disposto no número anterior os condutores e passageiros de veículos providos de caixa rígida ou de veículos que possuam, simultaneamente, estrutura de proteção rígida e cintos de segurança.

2010 Morgan +4
Me racing it: http://youtu.be/CQgT2vMLEUo
2014 M3W Brooklands
To be raced