Los Angeles County voters narrowly defeated Measure J, the proposed 30-year extension of a half-cent transportation sales tax.
Supporters estimated that the measure would generate $90 billion to pay for a network of light rail and subways.
The measure garnered 64.7% of the vote, narrowly missing the two-thirds majority required.
The sales tax would have extended Measure R, which had been approved in 2008 to run until 2039, by extending the tax authorization another 30 years to 2069.
That would have allowing the Los Angeles County Metropolitan Transportation Authority to sell additional bonds to access funds to accelerate construction projects.
Officials had hoped to use the additional money to tap into a federal loan program called the Transportation Infrastructure Finance and Innovation Act.