As General Motors Corp.'s (GM) medium-duty truck operation in Flint, Mich., gears up to produce two new vehicles this year, the various configurations of options are enough to boggle a corporate planner's mind. "It's important that we communicate to the operators how to build these vehicles, because the possible combinations are in the trillions," observes John Ninotti, director of medium-duty truck production operations. Each order is translated into a build documentation, or set of instructions that "tells the people on the line what to build," explains Wally Nabozny, materials director at GM's medium-duty truck operations. With about 450 workers, the plant, which also produces GMC pickups, builds the $35,000 to $80,000 cab-chassis combinations that later will receive bodies as garbage trucks, wreckers, snow plows and dump trucks. To deal with the complexity, GM has put a series of "error-free" systems in place designed to ensure that operators, who work in teams on the plant floor, assemble each vehicle exactly according to customer specifications. To that end, each operator has a computer screen describing which options dictate what parts to be picked for that vehicle. Any automaker offering "custom-equipped vehicles" -- e.g., cars or trucks fitted with a particular customer's order for specific features and options -- deals with similar issues. "What is happening on the assembly lines today is that the batches are becoming smaller, and there is more demand for options, so assembly lines are becoming more flexible," says Dilip Kembhavi, executive vice president at Matrikon Inc., a software firm in Edmonton, Canada. Matrikon's software, which is used by seven major automotive manufacturers, takes into account the OEM's rules that limit how many of a particular color or model can be built before making a change. The software assigns penalties for violating the various rules. "The goal of the system is to come up with a schedule that has the lowest number of penalties for the next month out," explains Kembhavi. Ford Motor Co. uses the Matrikon system to optimize schedules for 10 North American stamping plants. The software is especially useful to project "what-if" scenarios as business needs change. "If demand for a particular vehicle increases from 600 to 1,000 cars a day, it enables us to see if we can adjust our capacity," says Chip Conrad, planning group supervisor in Dearborn. Having everyone working off the same planning system also is helpful. "One of the biggest advantages with the common database is that all the information on press lines and all die and stamping information is there, so if a plant loses a line, we can see what other lines that work can run on," says Tim Marasco, business planning manager in Dearborn. "We are able to make much more intelligent decisions."