Tremont Street Subway started in New York.
The bilabial trill is a type of consonantal sound , used in some spoken languages .. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is B \ .. International Phonetic Alphabet. International Phonetic Alphabet. X-SAMPA. X-SAMPA. In many of the languages where the bilabial trill occurs , it only occurs as part of a prenasalized bilabial stop with trilled release , -LSB- -LSB- mbʙ -RSB- -RSB- .. This developed historically from a prenasalized stop before a relatively high back vowel , such as -LSB- -LSB- mbu -RSB- -RSB- .. back vowel. back vowel. In such instances , these sounds are usually still limited to the environment of a following -LSB- -LSB- u -RSB- -RSB- .. However , the trills in Mangbetu may precede any vowel and are only sometimes preceded by a nasal .. Mangbetu. Mangbetu language. A few languages , such as Mangbetu of Congo and Ninde of Vanuatu , have both a voiced and a voiceless bilabial trill .. Mangbetu. Mangbetu language. Ninde. Ninde language. There is also a very rare voiceless alveolar bilabially trilled affricate , -LSB- -LSB- tʙ -RSB- -RSB- -LRB- written in Everett & Kern -RRB- reported from Piraha and from a few words in the Chapacuran languages Wari ' and Oro Win .. trilled affricate. trilled affricate. Piraha. Piraha language#The bilabially trilled affricate. Chapacuran languages. Chapacuran languages. Oro Win. Oro Win language. The sound also appears as an allophone of the labialized voiceless alveolar stop -LSB-  /  tʷ  /  -RSB- of Abkhaz and Ubykh , but in those languages it is more often realised by a doubly articulated stop -LSB- -LSB- tp -RSB- -RSB- .. allophone. allophone. voiceless alveolar stop. voiceless alveolar stop. Abkhaz. Abkhaz language. Ubykh. Ubykh language. In the Chapacuran languages , -LSB- -LSB- tʙ -RSB- -RSB- is reported almost exclusively before rounded vowels such as -LSB- -LSB- o -RSB- -RSB- and -LSB- -LSB- y -RSB- -RSB- .. Chapacuran languages. Chapacuran languages