A video of a passenger bus emitting thick black smoke has raised safety and environmental concerns among motorists. Automotive publication VISOR on July 30 posted a video submitted by a reader showing an Alabang TSC bus traveling along a major road while emitting thick smoke from its exhaust pipe. Nakakalusot din sa smoke emission test? 8749, also known as the Clean Air Act, requires vehicles to comply with the emission standards set by the government. Last year, the Land Transportation Office (LTO) placed a passenger bus under alarm and summoned its owner after it went viral for emitting thick black smoke.