A rush-hour crawl that gave vehicles little momentum to slide into the river and a bridge design that minimized falling debris appear to have kept the death toll relatively low in the collapse of a bridge into the Mississippi River. After divers spent a second day searching the waters, the number of dead stood at five, and authorities cast doubt on an earlier estimate that as many as 30 people were missing. They even said it could be as few as eight. Barring bad weather, divers planned to resume their search Saturday for cars and bodies in the swirling, muddy currents. President Bush was also scheduled to visit. Of the roughly 100 injured in Wednesday's collapse, 28 remain hospitalized and only five were critical. "We were surprised that we didn't have more people seriously injured and killed," Minneapolis Fire Chief Jim Clack told The Associated Press. "I think it was something of a miracle." Clack cited a list of reasons: a bridge design that minimized falling debris, a quick response by rescue crews and the rush-hour crawl that kept more vehicles from plunging into the river. In addition, experts say the speed and depth of the water in the Mississippi River were much lower than normal on the day of the collapse - largely the result of a drought. That may have made it easier for people to escape the disaster. "It's a horrible, tragic event. But it could have been a hell of a lot worse," said Kent Harries, assistant professor of civil and environmental engineering in the University of Pittsburgh's School of Engineering. Minnesota officials say they don't yet know how many cars were traveling the span during the collapse. But judging by the length of road, the lanes that were open, time of day and widely accepted traffic formulas, Northwestern University engineering professor Joseph Schofer estimated that between 100 and 150 vehicles were on the bridge. Despite the low death toll, divers were still contending with a treacherous combination of sunken cars, broken cliffs of concrete and jagged rebar as they searched for bodies. Firefighters pulled the fifth victim, the driver of a tractor-trailer that was engulfed in flames, from the wreckage late Thursday. Video of the burning rig - nose down in the crevasse between two broken concrete slabs - was among the most compelling images shown in the immediate aftermath of the collapse. The driver was identified as Paul Eickstadt, 51, of Mounds View. Early in the day, authorities said as few as eight people were still missing. However, they cautioned later that number could rise, in part because there was no way to know how many victims were in the water. Some people without family in the area may not have been reported missing, said Police Lt. Amelia Huffman, a spokeswoman. The missing included a 23-year-old pregnant woman and her 2-year-old daughter, who was in the back seat of the family's car when the bridge crumbled. Sadiya Sahal, a 23-year-old immigrant from Somalia, called her family at 5:30 p.m. saying she was stuck in traffic, said Omar Jamal, executive director of the Somali Justice Advocacy Center. That was her last phone call. "Her husband is destroyed. He's in shock," Jamal said. Authorities still do not know what caused the 6:05 p.m. collapse. Engineers had theories including heavy traffic and construction work that might have put an undue burden on the span. The bridge was deemed "structurally deficient" by the federal government as far back as 1990. Minnesota transportation officials spent another day dealing with scrutiny arising from reports and inspections over the years that raised alarm about the bridge, including rust-eaten steel beams, missing bolts and cracks in the welding that held load-bearing parts together. A consulting company that thoroughly examined the bridge noted that one possible fix - steel plating of fractures - carried a "relatively high cost," according to a January report. Transportation officials deny that cost pressures swayed their decisions. First lady Laura Bush toured the scene Friday morning. She praised the rescuers who rushed to the bridge in the chaos after the collapse - a sentiment echoed by the fire chief in explaining why more people didn't die. Because the bridge was near the heart of downtown, several emergency crews and residents were close by. "We could not have done it as firefighters alone. It took more people than we had. It was organized. It was pretty calm," Clack said. Authorities and engineers agree that the truss-style design of the bridge played a big role in saving lives. The steel that supported the bridge was below the structure - as opposed to above the span in more traditional bridge designs. "I think that was a lifesaving feature," Schofer said. "They had this huge advantage. They weren't crushed by steel." Even though the collapse occurred during rush hour, the heavy traffic was an advantage because the cars were almost stopped and didn't have much momentum, Clack said. Because of that, the collapse was less likely to hurl moving cars into the river. "They didn't have forward velocity," he said, "so when the bridge fell, they went straight down." While the entire span covers 1,907 feet, only 458 feet is directly over water, supported by giant pylons. The rest of the bridge rises over the river channel's sloping banks and the adjacent flood plain. The irregular slope of the riverbank on the south side of the bridge turned out to be a good thing. When that portion of bridge snapped at the middle, the support pylons held, and the roadway only had a short distance to fall until it was caught by a drop-off just before the river. On the north side of the bridge, however, the bank slopes down in a steady angle to a broad flood plain. As a result, when that portion of the bridge crumpled, there was nothing to catch it. That was evident to Dr. John Hick, assistant medical director for emergency medical services at Hennepin County Medical Center, who noticed that injuries on the north end of the bridge were much graver. Another factor that may have limited the death toll is the behavior of the river itself. Mark Rosenker, chairman of the National Transportation Safety Board, said investigators were particularly interested in learning why a part of the bridge's southern span shifted as it collapsed. That was the only part of the bridge that shifted, and it could help pinpoint the cause. Scott Bratten, who regulates locks and dams on the river for the local district of the Army Corps of Engineers, said that because of the drought in Minnesota, the water at the time of the collapse was flowing at just a third of its normal speed. That may have made it easier for people in cars to escape them, and it almost certainly made it easier for rescuers to make their way into the water and help the dazed and injured. "During the spring it's a raging torrent in there and it would be a very dangerous place," said Whitney Clark, executive director of Friends of the Mississippi River. "The low water I'm sure was a factor in not making currents very much of an issue. ... If this had happened during the spring snowmelt or something it would have been a much different situation."