Manaus is a city in Brazil.
Southwest towards Porto Velho and Bolivia
Highway BR319 begins in Manaus heading southwest through the Amazon. It is quickly interrupted by a shorty ferry ride from Porto da Ceasa on Manaus' far eastern edge. The ferry will cost R10.00, leaving every hour on the hour or half hour depending. Chatting with people on the ferry you may find a ride further down the road.
Disembarking in Careiro da Várzea to your left walking down the road there is a trucking facility from where you will be told trucks leave for Porto Velho. You can hang around seeing what you can find or hitch a ride to Castanho (appears on Googlemaps as "Careiro"), the last town with the last gas stations for ~450km (until the town of Realidade). There are several speed bumps leaving Careiro da Várzea that make getting a ride quite easy, and there are only so many other places traffic can be heading.
TowellessTraveler went on this road in September 2022. If you arrive around noon in Careiro you might not find any truck drivers in the ferry nor the village. People say they come in the evening or the morning. You can still walk out of the city and a bus to Castanho might give you a lift. From there it's better to find a truck but it can take a lot of time. It is also possible to walk and get a lift from the only bus that goes until the ferry crossing in Igapo Açu (only one bus per day). You can stay on the ferry all the time and talk to the drivers while they wait. Do not go any further on foot, it's only the jungle after that until Realidade.
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