After two Metro trains collided in a fatal accident in 1996, the National Transportation Safety Board recommended that Metro strengthen the skeleton of its rail cars to prevent "telescoping," in which one train climbs up onto the roof of another and collapses into itself like a retracting telescope.

Metro did not follow that recommendation, saying it would be too expensive and disruptive to carry out, according to NTSB records.

Last week, a runaway train plowed backward into an occupied train at the Woodley Park-Zoo/Adams Morgan Station, coming to rest only after it had climbed onto the stationary train and collapsing into itself.

The question of whether Metro should have gone to the expense of rebuilding its old cars based on the NTSB review will be difficult to evaluate until the safety panel concludes its investigation into the Nov. 3 collision. Metro declined to discuss whether any of its decisions may have had an impact on the crash, referring all questions to the safety board.

But the transit system has said for years that it lacks enough money to maintain its existing fleet and has postponed important mechanical work on trains and buses.

The runaway train was empty except for the operator, who was in a cab at the other end of the six cars and was not hurt. Of the 70 passengers inside the other train at Woodley Park, 20 suffered minor injuries.

"At this point, we don't know the extent to which the 1996 recommendations relate to this crash," safety board spokeswoman Lauren Peduzzi said. "But any time we make recommendations with the goal of preventing a similar accident from happening in the future, it's always disheartening when we see an accident that could have been prevented."

At the scene of the Woodley Park crash last week, National Transportation Safety Board member Debbie Hersman said half the "survivable space" in the telescoped rail car was "lost."

After the federal investigation into the 1996 crash at Shady Grove, in which a train operator was killed, federal safety experts said Metro needed to strengthen its rail cars. "The safety board concludes that the design of Metrorail cars may make them susceptible to telescoping in collisions," according to the NTSB report. Metro should "make the necessary modifications, such as incorporating underframe bracing or similar features, to improve the crashworthiness of cars in the current and/or future Metrorail fleet."

That recommendation was among 20 made by the NTSB, most of which Metro adopted. They included revising Metro's operating manual, installing new software on trains and training more frequently with fire departments.

But on the issue of strengthening the structure of Metro rail cars, records released by the NTSB show a discussion that continued for years between Metro and the safety board about whether the transit agency would follow the recommendations.

The safety board has no authority to force compliance. It can only prod transportation agencies to follow its advice. About 80 percent of the recommendations made by the NTSB are adopted by transportation agencies, safety board spokesman Terry Williams said.

Metro hired a consultant, Booz Allen Hamilton Inc., to analyze the suggestion to strengthen the rail cars. In 2001, the transit system notified the NTSB that Booz Allen advised against retrofitting the rail car fleet because "the cars would have to be completely disassembled, the structure would have to be reworked, and the associated costs would be prohibitive," according to NTSB records. The consultant did not estimate the cost, Metro spokeswoman Lisa Farbstein said.

Instead, Metro said it would design future rail cars to better withstand crashes. The safety board wrote that although it is good to improve the design of future rail cars, Metro's existing fleet will be carrying passengers for years to come.

The runaway train was composed of six rail cars built in the 1970s. That generation of Metro cars is not scheduled for retirement until 2012. The occupied train hit by the runaway was made up of six cars built in the 1980s. That generation of cars is undergoing a midlife overhaul to extend its life by 20 years. Only Metro's 192 newest rail cars were designed to withstand crashes without telescoping. The other 760 cars have no such protection.

In 2002, Metro wrote again to the safety board, repeating that reinforcing the underframes of all of its rail cars was not practical. But Metro added a new argument: that strengthening the structure of the rail cars could cause more passenger injuries because it might transfer some of the force of a crash to the passengers instead of allowing the blow to be absorbed by the crumpled aluminum of a collapsed rail car.

Jack Corbett, a co-founder of MetroRiders.org, a new advocacy group representing passengers, said his organization wants an outside analysis of safety issues at Metro, including the crash worthiness of its rail cars.

MetroRiders.org is calling on Metro to seek a review of its financial, operational and safety problems by a panel of transit professionals from across the country.