The conflict between the cities is rooted in Catalans' historic desire to be treated as a nation equal to the Spanish, and not a subject province useful only for topping up Madrid's exchequer.
The latest skirmish began when the Catalan nationalist leader, Jordi Pujol, declared that the autonomous Catalan government, the Generalitat, was effectively a sovereign state and that, as regional premier, he should enjoy direct access to the king of Spain, bypassing the government in Madrid.
This aroused fury in Madrid, where Mr Pujol is portrayed as a calculating mendicant, rattling his tin for more pesetas. Barcelona's response is to remind Madrid that Catalonia is a net contributor to Spanish finances.
Then Mr Pujol declined to renew the broadcasting licences of three radio transmitters of the Spanish-speaking station, Cope, for Barcelona, Tarragona and Manresa, effectively closing them down. He accused Cope, which is the mouthpiece of the Spanish Bishops' Conference, of violating freedom of expression and of broadcasting untruths - a comment he later acknowledged was "a mistake". Mr Pujol is not unsympathetic to Cope's conservative Catholic message, but would prefer Catalan bishops to purvey it, in Catalan.
Disputes over regional powers produce deep resentments, which surface in slanging matches. One example is the case of two prominent Catalans accused of huge swindles while they were senior tax inspectors in the early 1990s. Josep Huguet and Ernesto de Aguiar are accused of salting away fortunes in Swiss bank accounts. During the easy-money 1980s and early 1990s, when entrepreneurs and politicians in Madrid perpetrated frauds galore, the Catalans prided themselves on their austere financial probity. Detractors from Madrid have seized with delight upon revelations of Catalan tax dodging. "The civilised, cultured, European, patriotic and honourable Barcelona that we've been sold as Spain's second capital turns out to be a poisonous web of complex, profound and organised corruption," sneered one of Madrid's most polemical commentators, Francisco Umbral, in El Mundo.
As for the jams, Madrid is recognised as a traffic nightmare, while Barcelona is by comparison a vehicular paradise, with good public transport and severe controls on cars. It was unwise of Madrid to compete with Barcelona on "car-free day", 29 April. In Madrid only 3 per cent fewer cars clogged the roads, while in Barcelona traffic dropped by 30 per cent in the centre.
The conservative mayor of Madrid, Jose Maris Alvarez del Manzano. then accused Barcelona of cheating by closing some roads to private vehicles. Barcelona, he added, "lacks the sense of liberty that Madrid enjoys". Barcelona countered that it had provided hundreds of bicycles, 90 per cent of which were used.
Such exchanges, however childish, reflect the permanent rivalry between the capitals of two peoples still haggling after centuries over the regional distribution of money and power. As for Barcelona FC and Real Madrid, that is a war without end.