Vaporis states himself that the purpose of the book is to "[...] examine Tokugawa society [...] through the prism of travel and transport." And in doing that, I think he does a mighty fine job. A great deal of the book looks at road barriers around the country and how these barriers restrained (or did not restrain) peoples physical mobility in the Edo period.
The book is thematically structured into six chapters plus an introduction and a conclusion. The chapters are laid out in a very logical order and the information in each chapter builds on the preceding ones. Throughout the chapters, however, he aptly uses repetition in such a way that each chapter can be read and fully understood on its own.
The first chapter is named The arms and Legs of the Realm and gives a thorough overview of the infrastructure of the gokaidō-network (a network of five roads, where the most famous ones are the Tōkaidō and the Nakasendō).
The next chapter, The Social Organization of the Gokaidō Network, deals for the most part with sukegō taxation, a kind of labor tax put on villages close to post stations on the roads. Neighboring villages were obligated to provide porters and pack horses if traffic became too much for the post station. The villagers were compensated for their efforts, but usually this did not make up for their lost time in the fields. Needless to say this led to complications between the villagers and the authorities.
Chapter three is named A Curious Institution and here Vaporis looks at the two kinds of barriers that were put up throughout the country, sekisho and bansho. He goes into rather impressive detail, and lists for instance how many guns, bows, spears and staves various sekisho had in stock. One of the main concerns for the sekisho was to monitor and prevent the movement of guns eastward towards Edo, and the movement of women westward away from Edo. The bakufu did not want guns in Edo in fear of an uprising, and women traveling away from Edo might have been hostages in the alternate attendance system (sankin kōtai).
The fourth chapter, Permits and Passages, investigates different kinds of passports and permits that were required to pass the various barriers and how they could be acquired.
Chapter five, The Benevolence of the Realm, gives a detailed description of various ways and methods to circumvent the sekisho system. There were for instance many side roads one could use to get around the barriers; women sometimes dressed up as boys to avoid attention; or one could simply bribe one's way through. This shows an inability or unwillingness from the authorities to fully enforce the system.
The last chapter, Travel as Recreation, deals with the emergence of a travel industry. Most travel at the time took the guise of pilgrimage, and pilgrimage was also one of the only legitimate reasons you could have for applying for travel permits. As time went by, however, pilgrimage became more and more secularized, and the visiting of shrines and temples became only one of the many stops on the journey.
Breaking Barriers is a well written book and is maybe most impressive in the plethora of sources it draws upon, both primary and secondary. Historians have often been criticized for analyzing society from a top-down perspective, looking mostly on the authorities and the elite often neglecting the majority of the population. Vaporis is definitely not of that kind. In this book he looks at society both from top-down, and bottom up. He looks at official documents and such things as travel diaries and travel guides. If we take the official documents at face value, early modern Japan indeed looks like a country where physical mobility was greatly hampered. When including the bottom-up perspective, we get a different story and the discrepancies between official policies and social reality is revealed. This is why this book tells us a great deal about society in the early modern period, not just travel in general. Go read!
Vaporis, Constantine Nomikos. Breaking Barriers: Travel and the State in Early Modern Japan, Harvard East Asian Monographs. Cambridge. Mass.: Harvard University Press, 1994.