Many of the travellers express great concern over the current clash between separatist leaders in the northeastern region and the central government, just two days ahead of an independence referendum banned by Madrid.
Beatriz Migens, a 43-year-old from the southern city of Seville, is travelling to Catalonia for the wedding of one her best friends, a Catalan.
Marisol Martin and her colleague Beatriz Barco have been invited by their employer, a lawyer's practice in Barcelona, to celebrate the firm's 100th anniversary.
Montse Rodriguez is going to see her parents in Manresa, a pro-independence town in the centre of Catalonia, a wealthy region which counts 16 percent of Spain's population.
Entrepreneurs Carles Rivadulla and Juan Arza are going home after a meeting with a client... and a conference against independence.
Every day, thousands of Spaniards make this trip in one direction or the other.
"Sometimes, they speak Catalan and if they see you don't understand, they switch to Spanish," says the train purser, who won't give his name.
'Will be problems'
Beatriz Migens, her long brown curls put back in a pony tail, talks a little nervously as the day rises over the Spanish countryside.
She lives two days a week in Barcelona and the remaining five in Madrid, and has been tasked with buying her friend a tie for his wedding on Saturday.
He has had to take the current situation into account when drawing up the table seating plan.
"He told me, there are two people, if I put them side by side, there will be problems" due to their political differences.
Migens has also decided to head back to Madrid promptly on Sunday morning, fearing unrest in Catalonia over the referendum which Madrid is determined to stop.
"I spend my day defending normal Catalans" while in Madrid, says Migens, a salesperson in a cosmetics firm, criticising both sides.
She points to the Catalans who repeat over and over that "Spain robs them" as they feel they pay more in taxes to Madrid than they get back.
And she also takes a dig at other Spaniards who take offence at the independence movement and tell me, "why don't you leave."
Catalonia itself, deeply divided over independence, is torn.
"My parents don't want independence, and consider themselves real Catalans, but among their friends, there are divisions, more and more conflicts," says Beatriz Barco, a 34-year-old secretary.
Staying indoors
Montse Rodriguez, 23, grew up in Catalonia but is happy to have studied law in Madrid.
Her mother is Catalan by birth while her father arrived from the sprawling southern region of Andalusia, from where many emigrated to Catalonia in search of a better life last century.
She loves both Madrid where "locals are very welcoming", and Barcelona which she feels is "more cosmopolitan".
The problem she said comes from politicians from both camps who are racing towards a head-on collision.
Spanish Prime Minister Mariano Rajoy has banned the referendum while Catalonia's pro-separatist government are determined to go ahead with the vote.
Rodriguez prefers not to say if she will vote or not on Sunday but she said she was not worried. It will be a "peaceful movement", she said.
But if fellow passenger Juan Arza heard her, he would not agree.
The human resources consultant, who studied political science, has vowed not to leave his home on the day of the referendum and will keep his two children, aged six and eight, indoors as well.
"I am very worried because I see my neighbours go out every night banging pots and pans, angrily," he said in a reference to a traditional form of protest in Catalonia.
"There is a very strong social malaise," he added.
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