MINNEAPOLIS -- A year after a freeway bridge in Minneapolis plummeted into the Mississippi River, the investigations and finger-pointing drag on.

Time-Lapse Photos Of Rebuilding

But one aspect of the Interstate 35W disaster -- replacing the collapsed span -- has zipped along.

A new $234 million bridge will open this fall. Crews have been working so quickly that the new bridge should be done before federal officials say for sure why the old one fell down.

"No question about it, this has been an extremely aggressive schedule," said Terry Ward, deputy project manager for the Minnesota Department of Transportation. "There's something happening on this project 24 hours a day, seven days a week."

The I-35W bridge collapsed at 6:05 p.m. on Aug. 1, 2007, killing 13 people and injuring about 100. Divers and other workers spent weeks recovering bodies and removing vehicles from the river.

Since then, little on the investigative front has moved quickly or harmoniously. Minnesota Gov. Tim Pawlenty, a Republican who is considered a contender to become Arizona Sen. John McCain's presidential running mate, urged Minnesotans not to jump to conclusions about the collapse.

But elected leaders from Minnesota's Democratic-Farmer-Labor party said the disaster exposed Pawlenty's mishandling of state roads and bridges. Some lawmakers said budget cuts and mismanagement are at least partially to blame for the disaster.

In May, a report mandated by the state Legislature concluded state officials may have missed opportunities to prevent the collapse. Pawlenty responded that no one has found evidence that maintenance decisions or state spending cuts played a role.

The federal probe won't be done until at least October. Investigators have analyzed tons of debris, pored over construction and maintenance records and studied images taken before and during the collapse.

In January, the National Transportation Safety Board stated some of the gusset plates holding together parts of the 1960s steel truss bridge should have been thicker, a design flaw that likely contributed to the collapse. Other factors still being examined include gusset plate corrosion and extra weight from construction equipment and supplies on the bridge when it fell down.

Final NTSB conclusions are expected in about 100 days. The new I-35W span will probably be open by then. The state hired the Flatiron-Manson construction team to build the bridge and offered a lucrative incentive for completing the project quickly. The deadline to finish the bridge is Dec. 24, but for every 10 days the span opens earlier, the builders will earn a $1 million bonus. State officials now say the bridge may open in late September or early October.

Work on the new concrete bridge has been literally nonstop. Over the winter, crews drilled deep holes into the bedrock on either side of the river and erected towering piers.

This spring and summer, cranes hoisted huge sections of the double-span bridge into place. This week, crews are pouring concrete to join the spans over the river.

So far, the project has consumed 50,000 cubic yards of concrete, 17 million pounds of reinforced steel rod and 1,000 miles of tensioning cable.

Even to a casual observer, the new bridge appears much sturdier than the old one. The 40-year-old structure that collapsed was a steel skeleton topped by a concrete road, all standing on thin piers.

The new bridge, built to last 100 years, is far more imposing. Unlike the old one, officials say, the replacement bridge has multiple redundancies, which means that if one piece fails, the entire span won't crumble.

The construction has become a spectacle. On Saturday mornings, sizable crowds gather on a nearby river bridge for walking tours led by construction managers.

The bridge won't open in time for the Republican National Convention, which runs from Sept. 1-4 in the Twin Cities. The convention happens at the Xcel Energy Center in St. Paul, but many VIPs, delegates and journalists will be staying in Minneapolis.

Businesses and residents are eager to start using I-35W near downtown Minneapolis again, said state Sen. Larry Pogemiller.

"It's been very difficult living without the bridge," said Pogemiller, whose district includes much of downtown Minneapolis. "People are really excited about what's rising from the ashes, and there's a general feeling that this project has not only been done quickly, it's been done right."

Minnesota and the rest of the nation should learn from the tragedy and the rebuilding, said Hennepin County Commissioner Peter McLaughlin, whose district includes both sides of the I-35W bridge.

"The bridge collapse remains to me a symbol of a state and nation that hasn't paid sufficient attention to its infrastructure," McLaughlin said. "The new bridge shows what we can do when we focus our attention and resources. Now let's move on to the rest of the system."