Why air brakes for truck and bus?

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<blockquote class="wp-embedded-content" data-secret="U40QgYtiYC"><a href="https://tommykwan.com/blog/my-diaries/why-air-brakes-for-truck-and-bus/">Why air brakes for truck and bus?</a></blockquote><iframe sandbox="allow-scripts" security="restricted" src="https://tommykwan.com/blog/my-diaries/why-air-brakes-for-truck-and-bus/embed/#?secret=U40QgYtiYC" width="600" height="400" title="&#8220;Why air brakes for truck and bus?&#8221; &#8212; Tommy&#039;s Diaries" data-secret="U40QgYtiYC" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" class="wp-embedded-content"></iframe><script type="text/javascript">
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