Five years ago, Fresno County voters overwhelmingly approved a 20-year extension of the half-cent transportation sales tax known as Measure C.

They were told that the measure would raise $1.7 billion for new roads, better bus service, street repairs, bike trails and scores of other improvements. And it might have, if the economy had cooperated.

Instead, a year after the extension went into effect, the real estate boom went bust. Sales tax revenues collapsed and took Measure C's budget with them.

Now, the Fresno County Transportation Authority projects it will collect at most $1.2 billion from the measure over 20 years -- almost one-third less than what was expected.

As a result, promises made before the Measure C vote are being broken:

• Highway projects are delayed, such as the Veterans Boulevard interchange with Highway 99. Some have been abandoned outright, including the extension of Highway 180 west to Interstate 5.

• A pledge of 15-minute bus service on major Fresno routes was rolled out, then rolled back. Meanwhile, fares have risen and free rides for people older than 65 -- another Measure C promise -- have been discontinued.

• Some cities facing budget deficits have stockpiled Measure C funds earmarked for street repairs, trails and similar uses. In one city, auditors say Measure C funds may have been been used to cover unrelated deficits.

So what went wrong?

Did the Measure C extension's authors oversell its benefits? Or did they simply fail to predict the future?

Mostly the latter, said Jeff Roberts, a Granville Homes vice president who represented the Building Industry Association in the Measure C extension talks in 2005.

"We might have been a tad optimistic, but we had a lot of experts working on it and I don't think any of them foresaw what happened with the economy," Roberts said. "The measure is working. It's just a little bit slower because of the revenues."

It could have been worse if not for some unexpected federal funding.

The federal stimulus program of 2009 provided $18.4 million for widening Highway 180 between Temperance and Academy avenues, where work was completed in October.

Another funding account is supplying $55 million for an expanded ramp network on Highway 180 between Highways 41 and 168, where construction is scheduled to begin next spring.

Those exceptions aside, projects delayed or canceled because of Measure C's shortfall already include:

• A new underpass for Herndon Avenue at the Union Pacific Railroad tracks, canceled.

• Widening segments of Willow, Ventura, Herndon, Shaw and California avenues, delayed by a year or more.

• Golden State Boulevard improvements through Fowler, Selma and Kingsburg, delayed five years to 2021.

• Improvements to the American Avenue interchange with Highway 99, canceled.

• A new bridge over the flood-prone Arroyo Pasajero on Highway 269 north of Huron, delayed five years to 2025.

Many of the delays have real consequences. "It's a nuisance," Huron City Manager Gerald Forde said of the flooding that closed Highway 269 two months last winter. "It means people have to take an alternate route to get into Huron or out of Huron, and both of those routes are about 50 miles."

Still more delays are likely if sales tax collections do not pick up sharply by middecade, as the authority now expects they will.

To make matters worse, a fee on new construction, enacted as part of the Measure C extension to help pay for major highway improvements, has produced one-third as much revenue as expected due to the recession and a delay in its implementation. That leaves another hole of more than $6 million.