Two aspects of the Paris rer pioneering phase in the 1960s and 1970s are particularly noteworthy. The first is the spectacular scale and expense of the enterprise. For example, FRF 2 billion were committed to the project in the budget of 1973 alone. This equates to roughly € 1.37 billion in 2005 terms, and closer to double that as a proportion of the region (then much smaller) economic output. This and subsequent spending is partly explained by the regional transport contribution, a small levy made on businesses that evidently benefit from the vast labour market put at their disposal by the Paris rer (see Paris rer map).

 

The Paris rer network came into being on 9 December 1977 with the joining of the Nation-Boissy and Auber-Saint-Germain-en-Laye segments as the eastern and western halves of the Paris rer Line A at Châtelet - Les Halles in the heart of Paris. The southern Ligne de Sceaux was simultaneously extended from Luxembourg to meet Line A at Châtelet – Les Halles, becoming the new Line B. The system of line letters in Paris rer map was introduced to the public on this occasion, though it had been used internally at RATP and SNCF for some time.

 

The Paris rer is operated partly by the RATP, the city transport authority that operates the Métro, and partly by SNCF, the national rail operator; the differences are of little concern to riders during normal operations because of the seamless fare structure and absence of transfers needed at SNCF/RATP boundaries. Total traffic on the central sections of Paris rer lines A and B, operated by RATP, was 452 million in 2006; total traffic on all lines operated by SNCF (both RER and Transilien trains) was 657 million passengers as its mentioned in Paris rer map.