Many parking fine evaders, drunk drivers and dangerous drivers are in a punishment scheme that ensures they are locked up at weekends but able to continue to work during the week.
Around 530 people are spending their weekends in Portugal's jails, according to data from the General Directorate of Reintegration and Prison Services.
The Free Days scheme means they spend Saturdays and Sundays in a prison cell, reflecting on their road crimes, alcohol-related driving and repeated failure to pay fines, many of them for parking tickets.
The detainees in this scheme represent about 4.4% of the prison population, currently numbering 13 12,877 men and 857 women convicts and pre-trial detainees.
The Free Days regime is applied to those sentenced to up to one year's imprisonment and after having exhausted all other alternative penalties, such as community work.
This regime allows the condemned to maintain some semblance of family life and to keep their jobs.
The detainees, who turn up for jail on Saturday morning and leave on Sunday night, share a ward and have no contact with full-time inmates.
The Justice Minister, Francisca Van Dunem, (pictured) does not like the scheme much and has set up a working group to look at replacing it with monitoring with electronic bracelets. This would help weekend overcrowding which needs extra staff.
According to the Ministry of Justice, one of the Government's priorities is to "strengthen the the national electronic surveillance system, particularly as an alternative to short-term prison sentences."