With a 16.5 km length , it constitutes a '' East - West '' route transportation important for the town of Paris : it is the most utilised subway line network with 161 million travellers in 2004 and 561,000 people per day on average .
With a 16.5 km length , it constitutes a '' East - West '' route transportation important for the City of Paris . 
 Excluding RER lines , it is the most utilised subway line network with 161 million travellers in 2004 and 561,000 people per day on average .