Toyota did not immediately comment on the report. Shares of the automaker climbed on the New York Stock Exchange following the news. Toyota shares were up more than 4 percent, to 89.00 in mid-afternoon trading.
Toyota paid the U.S. government a record $48.8 million in fines for its handling of three recalls. The company has said it has not found any flaws in its electronic throttle control systems and said the previously announced recalls have addressed the safety concerns.
LaHood said NASA engineers "rigorously examined" nine Toyotas driven by consumers who complained of unintended acceleration. NASA reviewed 280,000 lines of software code to look for flaws that could cause the acceleration. Investigators tested mechanical components in Toyotas that could lead to the problem and bombarded vehicles with electro-magnetic radiation to see whether it could make the electronics cause the cars to speed up.
A preliminary part of the study, released last August, failed to find any electronic flaws based on a review of event data recorders, or vehicle black boxes.
Despite its findings, LaHood said the National Highway Traffic Safety Administration was considering new regulations to improve safety. They include requiring brake override systems on all vehicles, standardizing keyless ignition systems and requiring event data recorders, or vehicle black boxes, on all new vehicles.
Transportation officials said they would also consider conducting more research on electronic control systems and review the placement and design of accelerator and brake pedals.
In Tokyo on Tuesday, Toyota reported a 39 percent slide in quarterly profit but raised its full-year forecasts for earnings and car sales. It is a mixed picture for the automaker, which is enjoying booming sales in high-growth markets in Asia, Africa and South America, while facing lingering worries about quality lapses in the U.S.