Some cities embrace neighborhood funded programs, for example, in Sacramento, CA:

If your street qualifies for speed lumps, but has not been funded by the City, you may pay for installation yourself. The cost will include design, construction and inspection of the City, speed lumps. Your street must meet all qualifications including two-thirds majority approval through the ballot process. Your neighborhood must have the funding and obtain approval from the Department of Transportation before speed lumps may be installed. The cost of a speed lump and associated signage is approximately $3,000.

http://www.cityofsacramento.org/Public-Works/Transportation/...