It  is clear that the three oldest underground systems are larger and serve significantly more passengers than the newer systems.
The London 
underground
 is the oldest Change the capitalization
Underground
system
, having opened in 1863. It is Use synonyms
also
 the largest Linking Words
system
, with 394 Use synonyms
kilometres
 of route. The Use synonyms
second
 largest Linking Words
system
, in Paris, is only about half the size of the London underground, with 199 Use synonyms
kilometres
 of route. Use synonyms
However
, it serves more people per year. Linking Words
While
 only Linking Words
third
 in terms of size, the Tokyo Linking Words
system
 is easily the most used,with 1927 million passengers per year.
Of the three newer networks, the Washington DC underground is the most extensive, Use synonyms
with126
 Correct your spelling
with 126
kilometres
 of route, compared to only 11 Use synonyms
kilometres
 and 28 Use synonyms
kilometres
 for the Kyoto and Los Angeles systems. The Los Angeles network is the newest, having opened in 2001, Use synonyms
while
 the Kyoto network is the smallest and serves only 45 million passengers per year.Linking Words