Maybe the issue aught to be the design of audible traffic signals, rather 
than the existence of them at all.  Many issues are changing and need to be 
considered.
1.  Who are the blind people?  More and more, they are older, have other 
mobility related disabilities, and are new to vision loss.
2.  Cars are quieter, and convey less audible information.
3.  Drivers are more distracted, what with texting, gps screens, and visual 
displays on the instrument pannels.

4.  Intersections are becoming more complicated.  Right and left turns on 
red, multiple streets, turning lanes, and round abouts.

5.  The dangers of the silent hibread cars are here.  The needs of the 
pedestrian need to be taken in to account now.  Retro-fitting will always be 
more expensive.

Theese concerns are pedestrian concerns, not just blind people's concerns.
Certain national organizations that insist that "blindness is only an 
inconvenience" need to get their heads out of the sand.  Sighted people do 
not know enough, and have no inclination to learn enough, to make that in to 
a reality.
In a perfect world maybe so, but we live in an imperfect world.  The only 
realistic option to an imperfect world, is to have no world at all.  Some 
people think that's where we are going.

If the sighted people get information on when and when not to cross, it is 
totally reasonable that we get the same information provided to us.

Their are many existing, and emerging technologies to make this both usable 
and safe to use.  A major need is that the information be selectable by the 
pedestrian rather than constantly apearing, whether it is needed or not for 
the particular light cycle.

The costs of not providing the equal information to all users of an 
intersection need to be considered.  This includes hospitilazation, 
rehabilitation, and nursing home care for the accident victims.