They're building a buffer zone here to reduce the traffic noise.
Examples (Wiktionary)
Mandarin
a,o,e开头的音节连接在其它音节后面的时候,如果音节的界限发生混淆,用隔音符号(’)隔开,例如:pi’ao(皮袄)。
a,o,e開頭的音節連接在其它音節後面的時候,如果音節的界限發生混淆,用隔音符號(’)隔開,例如:pi’ao(皮襖)。
a , o , e kāi tóu de yīn jié lián jiē zài qí tā yīn jié hòu miàn de shí hou , rú guǒ yīn jié de jiè xiàn fā shēng hùn xiáo , yòng gé yīn fú hào ( ’ ) gé kāi , lì rú : pi ’ ao ( pí ǎo ) .
[In Hanyu Pinyin], when a syllable beginning in a, o or e is preceded by another syllable, if the division between the syllables is unclear, use the syllable-dividing apostrophe (’) to divide [the syllables]. For example: pi’ao 皮襖/皮袄 (pí'ǎo).
In Zhuang, syllables in multisyllabic words are distinguished according to the syllable structure and tone symbols... When the syllables still cannot be distinguished accordingly, an apostrophe "'" needs to be used to divide the syllables