I want to know the answer to the following question:
What feature added in 2007 facilitated bus travel by London' passengers with hearing and vision impairments?
All the background I'm provided with is that "London has the largest wheelchair accessible network in the world and, from the 3rd quarter of 2007, became more accessible to hearing and visually impaired passengers as audio-visual announcements were introduced.". Is that enough to answer the question?