WPI
Journal

Summer 1997

Stirring the Pot

By Michael Dorsey


He developed a novel way of studying the workings of the cell.
He helped invent dynamic flight simulation and trained X-15 pilots and Mercury astronauts for their missions. He helped lay the groundwork for the Consumer Product Safety Commission when the idea of product safety was in infancy. But Carl Clark's most lasting legacy is his pioneering work in auto safety. From the first working airbag restraint system, to safer car windows, to such forward looking ideas as airbag bumpers, he's worked tirelessly to reduce the carnage on American roadways.


Carl Clark '45 doesn't hesitate to admit that he's something of a troublemaker. For more than 30 years, he's made trouble for industries and other institutions that have the power to make people's lives safer, but don't use it. Appalled by the millions of needless deaths and injuries that have occurred in those three decades, he's fought for safety in the face of the indifference and inactivity of organizations that were often too concerned with the quest for profits, too mired in bureaucratic red tape, or too bound up by political pressure to devote themselves to protecting lives.

Clark's interest in safety crystallized in the mid-1960s when, as a researcher at the Martin Company in Baltimore, he developed the first working automotive airbag safety system and conducted the earliest public experiments that demonstrated that the new technology could save lives. When the automotive industry sought to discredit his work, he persevered in promoting the technology in public forums. His persistence is probably an important reason that airbags are found in virtually all cars made today.

The automotive airbag research was just one element of a long and amazingly diverse career that has taken Clark to leading edge of such fields as optics, flight simulation, consumer protection, satellite communications and automotive safety. He has earned degrees in physics and zoology, has taught physiology, safety and accident reconstruction, and has conducted research on such wide-ranging topics as biological pigments, aviation medicine and the biological effects of high-energy radiation. Throughout his career, the glue that has bound his many interests and activities has been his abiding concern for the health and welfare of people.


Clark (center) designed the first working airbag restraint system, originally developed for spacecraft. He tested it himself by lying between two airbags in this box, which was repeatedly dropped from increasing heights.


Clark attributes his sense of social responsi-bility and his willingness to persevere in the face of daunting odds to his family history. He says ancestors going back at least three generations on both sides of his family tree were Congregational missionaries stationed around the world. "So this sense of trying to change things is in the family - we're busybodies," he says. "It gets us into trouble frequently, but it leads us into interesting things."


"We pushed ourselves right up to the limits. I was unconcious on the centrifuge perhaps 10 times."


At the Aviation Medical Acceleration Lab, Clark ran what was the largest human centrifuge. He developed methods to dynamically simulate actual flight accelerations and then trained the X-15 pilots and Mercury astronauts.


Clark's father became an electrical engineer, rather than a missionary, but with his inter-national background (he was born in Japan), he ended up in Asia as an engineer with General Electric's international division. Clark was born while his family was in Manila. Two years later, his father died and his mother moved the family to Vermont, where they had ancestral roots.

In high school, Clark became interested in science and mathematics and enrolled at WPI when the school offered him a scholarship. To earn money for expenses, he worked as a night clerk in a funeral home, a job he says may have contributed both to his developing interest in biology and his empathy for people in need. Having started out to be a mechanical engineer, he switched his major to physics, with the intention of going on to do graduate work in biology.


"The auto companies did some work before my studies. But their technical work was done in secret. Our's was the first published technical work, and they didn't want us stirring the pot."


After graduation, he became a lab assistant at Amherst College, where he also took undergraduate and graduate biology courses (a subject not taught at WPI) and broadened his background in the humanities. He spent the next summer studying at the Woods Hole Marine Biological Laboratory and then enrolled at Columbia University as a graduate student in zoology.


Clark's airbag systems proved themselves in a variety of tests. Here, he is the test subject as a rig outfitted with his airbag restraint system is swung at high speed into a wall.


For his thesis work, he studied the physiology of the living cell by looking at the streams of molecules that enter and leave it. "I was trying to learn about the dynamic chemistry of the cell," he says, "something that I still think will be valuable in identifying the cause of many illnesses."

Clark's graduate research resulted in articles in the international journals Science and Archives of Biochemistry and Biophysics. In 1951, he accepted an appointment as an assistant professor of zoology at the University of Illinois, where he taught for five years. "I continued my study of dynamic cell chemistry," he says, "while many of the faculty in the department were identifying the clams in the Illinois River. I just didn't seem to fit in there."


See also Corollary: The Science Behind Coca Cola Green

Having developed airbags for spacecraft and airplanes, Clark realized they had greater potential for saving lives in automobiles. Here he demonstrates part of a comprehensive automotive airbag safety system he developed while at Martin Company.


As a graduate student, Clark had worked in the infrared spectrophotometry laboratory of James D. Hardy at Cornell Medical College. Now Hardy, who'd moved on to become director of research for the Aviation Medical Acceleration Laboratory at the Naval Air Development Center outside of Philadelphia, came to Clark's rescue by asking him to become director of the lab's Biophysics Division.

The move represented a dramatic change in focus for Clark: from the individual cell to the human organism. Like Hardy, he accepted a joint appointment at the nearby University of Pennsylvania School of Medicine, where, as a research assistant and later an assistant professor of physiology, he gained a broader perspective on the functioning and limitations of the body.


One current project is developing safer, glass-plastic side windows for cars. The "T" edge he developed would help side windows become safety nets for passengers in rollover accidents.


Part of Clark's job at the Aviation Medical Acceleration Lab involved conducting experiments and pilot training using a giant centrifuge that could spin human beings at high speeds, simulating the G forces pilots encountered in jet aircraft. When he arrived, the centrifuge, with its 50-foot arm and 4,000-horsepower motor, was being used primarily in what he calls the "merry-go-round mode," but he knew the machine had gimbals that permitted the gondola to be tilted in virtually any direction as it was spun around. These could, with proper control, permit a pilot to experience the effects of changes he made in the attitude of his simulated airplane.

With colleague Richard Crosby, a mathema-tician, he decided to drive the centrifuge with some early analog computers. They installed mock cockpits in the gondola and wrote algorithms that caused the gondola to roll, yaw and pitch in direct response to the pilot's movement of the control stick. While the system worked, they quickly realized it could benefit from more computing muscle.

They received permission to connect the centrifuge to the ENIAC II computer, which had been installed at the Naval Air Development Center. ENIAC II was a cousin of the original ENIAC, the world's first large electronic analog computer." We were there at the beginning of dynamic flight simulation, though it has never been recognized in the literature," Clark says. "We made a real breakthrough."


From his home office in Baltimore, Clark continues hiw work in auto safety.


In the latter half of the 1950s, the United States began turning its eyes toward space and thinking about how men and machines would perform in that alien environment. Thoughts were already drifting toward interplanetary travel and the prospect of sending manned missions to Mars. "A trip to Mars was expected to take six months," he says. "The engineers worried about how humans would hold up during such a long flight. 'We have the machines,' they'd say, 'it's the human beings that are the problem.'"

Clark says the travel time to Mars during its closest approach to Earth could be cut to just two days if the spacecraft could be accelerated continuously at two times the force of gravity for half of the voyage and then decelerated at the same rate the second half. But nobody knew then how continuous acceleration for such a long period might affect human physiology. To find out, Clark climbed into the centrifuge during the Thanksgiving weekend of 1957, had it spun it up to 2 Gs, and stayed there for 24 hours.

Reclining in a contoured couch, he found that he could cook on a hot plate, sleep - even stand and move to a certain degree. A film made of him in the gondola shows the skin on his face pulled back as if he had developed jowls. The experience left him groggy and tired, but convinced that a fast trip to Mars was possible (in fact, it would the need for new developments in engine technology, not human capabilities, that would stand in the way of such a voyage).

During the simulated flight, he took advantage of the opportunity to conduct experiments on the Coriolus illusion, a problem that affects centrifuge riders. "You have to be careful about moving your head when the centrifuge (or a rotating space station) is spinning so as to avoid becoming nauseous," he says. "I explored that. I wanted to see at what point it becomes serious. I moved my head at various rates to controllably go up to the point where I was throwing up. I got some of the first numbers on the disorientation effects of head motion under centrifugation."

He says it was common for the scientists who ran the centrifuge to use themselves as test subjects. In fact, he notes, they would often expose themselves to conditions more severe than those the pilots and test subjects experienced. "We pushed ourselves right up to the limits," he says. "I was unconscious on the centrifuge perhaps 10 times. That was the whole atmosphere then."

In 1957, Clark was named program director for a project that contributed to the design and testing of the X-15 experimental aircraft. Clark and his team would also be responsible for using their expertise in dynamic flight simulation to conduct training exercises for the X-15 pilots and to demonstrate that the pilots could withstand flights in the craft, which was designed to travel at more than 4,000 miles per hour to altitudes in excess of 100 miles. The simulations contributed to the design of a special head restraint developed for the X-15 and demonstrated the need for replacing the traditional center-stick control with side-arm controls that pilots could more easily manipulate under high Gs. Most important, they familiarized the X-15 pilots with normal and emergency flight acceleration conditions before they made actual flights.

As a result of the X-15 work, Clark was named "Civil Servant of the Year" by the Federal Business Association. The work also led to a contract to train the seven astronauts chosen to inaugurate America's manned spaceflight program by flying the tiny Mercury capsule into Earth orbit. A full-scale, working simulated capsule was installed inside the gondola and the astronauts flew simulations of normal and emergency flight procedures. Two emergency maneuvers were of particular concern to NASA. The first, a launch abort requiring the use of the rocket-powered escape tower, would expose an astronaut to 11 Gs. Even more severe was an emergency reentry, which could generate up to 25 Gs.

"An astronaut would have experienced 11 Gs when the escape tower fired and again when the rockets shut down and the capsule was slowed by air resistance," Clark says. "People had never been through that experience. I did the initial trials myself. In small steps, we spun the centrifuge up to 11 Gs and then quickly turned the gondola 180 degrees to get 11 Gs in the opposite direction. It was an imperfect simulation, because as the gondola turned, we had to rotate through the point where my feet were facing down and much of the blood drained from my brain. I was right at the edge of unconsciousness and experiencing tremors. The astronauts themselves were trained only up to 6 Gs."

The 25 G emergency entry nearly put a halt to the Mercury program, Clark says, because the Washington physician advisors didn't think people could live through such extreme forces. "It wasn't until Carter Collins, lying in the special custom molded couch that NASA designed for the Mercury capsule, withstood 25 Gs on the centrifuge and walked out of the gondola, that they dropped their reservations."

In 1961, astronaut Alan Shepard rode the first Mercury capsule into space in his historic suborbital flight. That same year, Clark agreed to become head of the Life Sciences Division of the Engineering Department at Martin Company, the Baltimore-based aerospace firm. Martin built the Titan ICBM, which would become the launch vehicle for the two-man Gemini spacecraft. It was also hoping to make a bid for a piece of the multi-billion-dollar Apollo moon landing program.

It was at Martin Company that Clark's interest in airbags first developed. In his last year at the Aviation Medical Acceleration Laboratory, Clark had conducted tests of a belt/vest restraint system proposed for aircraft that used low-pressure airbags to tighten the restraint. He was also aware of airmats developed for the "snatch landing" of aircraft, and of airbags used to soft-land missiles. Having seen the expense involved in custom-molding a special couch for each Mercury astronaut, at the Martin Company he proposed that the Apollo spacecraft use an inflated air seat that would self-conform to the shape of its occupant. In addition to providing a seat that could be easily deflated and stowed, an air couch, in combination with an airbag deployed above the couch, could offer astronauts exceptional protection in a crash landing, he noted.

He developed a test unit inside a large box and became the first person to crash test an airbag system. He lay down inside the box between two airbags as the box was dropped from increasing heights. "We found that if you move the whole body as a unit in a controlled manner in a crash, the G levels experienced by the body are significantly lower than those experienced by the box," he says. "I later wrote a chapter in a book that explained that in a crash, it isn't the rapid deceleration that's dangerous, it's the distortion of the body as a result of deceleration. The trouble with seat belts, for example, is that they are only 2-inches wide. They work fine at low speeds, but at speeds above 35 miles per hour, they crack your ribs."

His work resulted in a government contract (the first ever awarded for work on an airbag safety system) to experiment with spacecraft airbags. Although NASA did not incorporate the system into the Apollo spacecraft, the work led to research on an airbag system for airplanes. Like the Apollo unit, the system included an airbag and an air seat.

The system was tested successfully by launching it on a Federal Aviation Administration catapult in Atlantic City, N.J., where it offered protection in crashes that produced velocity changes of more than 100 miles per hour. The system also performed well in several airplane and helicopter crash tests. In one test, the FAA crashed a DC-7, loaded with instruments, cameras and an assortment of experimental safety devices, into a hill at 160 miles per hour.

As it happened, Life magazine and NASA had installed cameras to record the drama inside the cabin. The photos appeared in the June 12, 1964, issue of Life. "The cameras caught special backward facing seats falling over, dummies in forward facing seats breaking their heads off on the seatbacks, and other assorted mayhem," Clark says. "But the dummy in my test seat went forward into the airbag and then gently floated back into the seat. He hit the bag again as the plane slammed into a second hill, then floated back to the seat. I figured the dummy may have experienced 5 Gs. It was obviously a breakthrough in crash protection."

Aircraft makers and airlines showed little interest in the airbag system. Government regulations did not (and still do not) require manufacturers to provide high-G protection to airline passengers, so airbags seemed a needless expense. "But this is something that's still needed," Clark says.

Clark was already exploring another potential market for airbags. Recognizing that far more people die on the roads each year than in the air, he began work on an airbag safety system for automobiles, which became known as the Airstop Restraint System. The system employed reusable airbags mounted at various points in the car (including a dashboard bag for the chest and a separate bag for the legs), air seats, pressurized air canisters to inflate them (the canisters could be refilled at a service station air pump), and a radar system to detect an imminent crash and inflate the bags just before impact. The radar system would have provided just enough time to inflate the bags - at low pressure.

The bags installed in cars today, Clark says, are triggered by the rapid deceleration of an actual impact. They use the ignition of sodium azinide to create the rapid, high-pressure inflation needed to fill the bags fully in the few milliseconds between the time the collision begins and the time the occupant strikes the vehicle interior. It is this high-speed inflation that has been implicated in the injury and death of a number of adults and children.

"They now say that airbags have killed more children under 12 than they've saved," Clark says. "That's sad. A slowly inflating airbag would gently push a child back and cause no injury. In the early 1970s, Toyota, perhaps partially as a result of my suggestion, developed a radar crash anticipation system to trigger airbags, but abandoned it. I understand that the idea is now being considered by other auto makers. Still, this valuable technology has been lost for 25 years."

As his airbag work progressed, Clark got his first real taste of the competition that can develop within corporations between the desire to serve the public good by making safer products and the need to continue to make profits by maintaining the status quo. As a result of a merger with Marrietta, Martin Company acquired a line of paints sold to auto makers. Not long after the merger, Clark discovered that this group of customers was anxious to keep his work under wraps.

Already, Clark had learned that he was not the first person to consider putting airbags in cars. Patent attorneys for Martin had found existing patents for airbag restraint systems for cars and airplanes, although none had ever undergone controlled tests. He learned later that a number of auto makers had conducted limited tests of airbag components but had decided not to pursue the technology. "The auto companies did some work before my studies," Clark says. "But their technical work was done in secret. Our's was the first published technical work, and they didn't want us stirring the pot."

But stir the pot is exactly what he did. In 1966, Ralph Nader and Clark were invited to testify at a hearing before the Iowa state legislature, which was considering the nation's first law to require seat belts in automobiles. Clark talked about the additional protection that airbags could provide. A year earlier, Nader had quoted Clark in his landmark book, Unsafe at Any Speed, which chronicled the auto industry's reluctance to make safer cars.

With others at Martin, he designed a conceptual safety car that became the first prototype car to have airbags - at least on paper. The car also incorporated a host of advanced safety features, some of which have only recently been employed or suggested for production model cars. They included a collapsible steering column, "heads-up" displays for the driver, a unitized passenger compartment, an energy-absorbing structure around the engine compartment, a fire suppression system, and tail lights and signal flashers mounted on the car roof to make them more visible.

The New York Times published the drawing of the safety car and an article about Clark's work on automotive airbags on Jan. 12, 1966. In the story, he foretold the danger modern, high-pressure airbag systems would pose to children. "The 'explosive' system would be harmless to seated passengers, Dr. Clark says, but could seriously injure a child who happened to be standing up when it went off. That's why slower inflation would be required," the article reported.

After the story came out, Clark got a phone call at his office from artist Salvador Dali. "He said he was intrigued with the concept of a billowy thing that will protect you in a crash, and asked me to have lunch with him," he says. "I felt I had to get permission from management, and the upshot is I didn't go. I've kicked myself ever since."

In 1965, Clark and a colleague presented a paper on the Airstop Restraint systems at the annual Stapp Car Crash Conference. The paper explained that lap belts (then available in few cars) are inadequate to prevent serious injury and death even in collisions at speeds as low as 20 miles per hour. It explained how airbags - deploying from several directions - and air seats could restrain passengers and offer protection even at highway speeds. The paper contained the first pub-lished description of a side airbag system.

"That paper really got people thinking," he says. "Afterward, the auto companies worldwide began working on airbags. Ford and General Motors had done some work in the U.S., but companies like Volvo and Mercedes Benz hadn't done any work up to that point. By 1966, they were all looking at the technology and wondering what to do with it. I took a system the auto companies wanted to ignore and put it in the spotlight."

Just how much the auto companies wanted to maintain the airbag's low profile became clear when the U.S. House of Representatives invited Clark to testify on auto safety as part of hearings on the need for a federal agency to regulate consumer safety. Clark asked the legislative committee holding the hearing to send a formal letter of invitation to his superiors. As the date for his testimony approached, he learned in an urgent phone call from Washington that the letter had been sent, but never responded to.

"Martin didn't want me to talk," he says. "They finally decided to let me testify, but I spent two days with the chief engineer, the legal counsel and other executives who urged me to say that I didn't fully understand the implications of my experiments. I did appear at the hearing, but the atmosphere at Martin was so clouded after that that I decided to leave.

"It was frustrating to see the opposition of the auto companies. They would tell my bosses that their research showed that airbags don't work, at the same time that I was doing work that showed that they worked very well. They also advanced the notion that everybody dies in catastrophic crashes and that there was nothing that could be done, except to try to educate the 'nut behind the wheel.' But some people do survive serious crashes, and they should have been asking why some people live. Despite my work and the concepts we and others demonstrated with our concept cars, they insisted that, while the systems might be effective, they were just too expensive."

In 1966, Clark founded Safety Systems Company, a research consulting firm he has maintained ever since. The company enabled him to continue to explore his interest in automotive safety. A year later, he accepted a post as associate chief of the Science and Technology Division at the Library of Congress. In 1969, he was asked to head the Task Group on Industry Self-Regulation of the National Commission on Product Safety. The commission was the first step toward the creation of the Consumer Product Safety Commission in 1972.

The task group was directed to investigate how effectively industry could regulate itself and produce safe products. "The commission looked at safety in the home and found that we were killing 30,000 people a year in preventable accidents - like people slipping on rugs and infants getting their heads stuck in the gaps in crib rails. Our group looked at what industry was doing. We concluded that they were not going to solve many safety problems on their own. The profit motive was just too strong"

Clark spent a year as a staff consultant in consumer product safety at the National Bureau of Standards and in 1972 was asked to help establish and serve as the first head of WPI's Life Sciences Department (now the Biology and Biotechnology Department). "For many years, I had been saying to WPI that engineers have to understand biology," he says. "They must have an appreciation for the people who use and control the equipment they design. I set it up as a fairly classical department, emphasizing an appreciation of life and biochemistry. But I'm not a money-maker, and WPI felt that I should have been out raising funds. After two years, I was asked to step down, and I did."

He returned home to Baltimore and became a member of the senior staff of the Monsour Medical Foundation. His focus was using computer and communications technology to address issues in community health. He set up a computer database (using punch cards) that helped community groups save time and money by finding out if other groups had already solved problems they were facing. He also organized demonstration projects using a set of experimental NASA satellites, conducting two early medical conferences by satellite. "After three years, the foundation reduced the amount of money it wanted to spend on this type of thing, so I had to look at other pastures," Clark says.

Those other pastures would take him back into the world of automobile safety. From 1977 until his retirement in 1990, he worked as a physical scientist in the Office of Crashworthiness Research at the National Highway Traffic Safety Administration (NHTSA). There, he became involved in an area of research that continues to occupy him today: how to prevent ejections through the side windows of cars and trucks. About 10,000 people die each year after being partly or completely ejected from their vehicles during crashes (most of the victims are not wearing seat belts). About half of those deaths occur when people are ejected though side windows, often in rollover crashes.

Clark says the major culprit in side window ejections is the tempered glass that auto makers have chosen to use in these windows since the late 1950s and early 1960s. Tempered glass is sometimes called safety glass for its tendency to shatter into small rounded pieces - under ideal conditions. It is less expensive than the laminated glass used in auto windshields, which is made by sandwiching a sheet of polyvinyl butyral between two sheets of glass.

The plastic layer in laminated glass can prevent missiles from penetrating the passenger compartment of a car and can keep an occupant from penetrating the window in a crash. The lamination also holds the fragments of a broken window together, preventing sharp pieces of glass from flying around and causing lacerations. If an additional layer of plastic is added to the inside of the windows (called glass-plastic glazing), occupants are also protected from lacerations caused by contact with a broken pane.

Tempered glass, on the other hand, generally shatters in a crash - often due to the strain placed on the window frame. And studies conducted by Clark and others have demonstrated that when tempered glass breaks under strain, it forms large, sharp fragments that can fly through the passenger compartment at high speeds. These fragments are responsible for serious laceration injuries in about 200,000 people annually. "These fragments cause terrible injuries," he says. "People have had glass removed from their brains after accidents. And yet the industry continues to say that tempered glass breaks into tiny, nonsharp cubes that don't hurt anyone."

Clark has conducted a number of laboratory and crash tests that demonstrate that glass-plastic side windows could prevent most of the laceration injuries that occur in crashes and also significantly reduce ejection deaths and injuries. When concerns were raised about the tendency of glass to pull out of a window frame when it is broken, he designed a T-shaped plastic strip than can be bonded to the edge of the window. The "T" sits in the window channel and prevents the glass from pulling out, enabling the plastic layer to become a strong "safety net" that keeps passengers inside the car.

Despite Clark's positive test results, auto makers have been reluctant to make the change and have disputed his and others' claims about the risks of tempered glass.

Still, change may be in the wind. The NHTSA has continued the studies of glazing that Clark started and has begun to lay the groundwork for possible new regulations requiring glass-plastic side windows. A number of European and Japanese car makers plan to offer laminated or glass-plastic side windows as an option. For those companies, the motivation for change seems not to be safety, but rather the concern of car buyers that the ease with which tempered glass shatters makes cars too vulnerable to break-ins.

In addition to continuing his work on car windows, Clark has been conducting tests of a new use for airbags - airbag bumpers. He says the concept is a reaction to the fact that about half of the serious injuries in automobile accidents are related to the intrusion of parts of the car into the passenger compartment. He notes that today's smaller cars have little in the way of a "crush zone" to absorb the energy of a collision. In addition, bumpers, which by law must be strong enough to withstand crashes of just five miles per hour, provide little protection in accidents at higher speeds.

The idea of temporarily extending the crush zone of a car was first developed in the early 1960s by James Ryan, a mechanical engineer at the University of Minnesota. Ryan designed and built a hydraulic bumper that would extend about 17 inches when the car traveled over 20 miles per hour. In tests, Ryan showed that a car thus protected could be driven into a wall at about 20 miles per hour with no significant damage to the vehicle or driver.

At 400 pounds, Ryan's system proved too heavy to be taken seriously by auto makers. Clark's system replaces the extendible bumper with lightweight airbags that would project several feet in front of the car just prior to a crash, triggered by the same kind of radar detection system he originally proposed using with passenger airbags. So far, a number of experiments and crash tests with pre-inflated airbags have been undertaken. The results, Clark says, indicate that an airbag bumper (in combination with occupant airbags) could protect occupants from serious injury in a crash into a wall at up to 50 miles per hour.

"It's feasible and it will be used in cars," says the man who crusaded for passenger airbags long before the auto industry and federal regulators were ready to think about them. "It just takes time to knock heads enough to get things to begin to happen."

Airbag bumpers may show up in cars long before another Clark innovation, the only safety device for which he has "afforded" a patent (awarded in 1973). "It's called the retrorocket brake, and it really is something for the future," he says. "It will probably only come about when cars routinely travel above 100 miles per hour. Auto companies say that if you put your foot on the brake and you start to skid, that's an 'act of God' and there's nothing they can do about it. But you need to provide a way to develop a force counter to vehicle motion, other than friction, because friction can take you only up to about 1 G - typically 0.7 G on dry surfaces."

Clark's design calls for a solid-fueled rocket with two exhaust ports located on either side of the car, facing forward. The thrust of the rocket could slow a car from 55 miles per hour to 8 miles per hour in just 23 feet of travel. The obvious hazards associated with driving around with a rocket under one's car could be ameliorated by using a rocket that expels water at high pressure, instead of hot exhaust. "Why is it that we accept a vehicle crashing when the driver has her foot on the brake and intends to stop?" he wrote in a 1983 memo to others at the NHTSA. "We are providing inadequate control capability."

Clark says he is not ready to fight any battles over retrorocket brakes. But the question might be asked, why does he continue to wage the campaigns in which he remains engaged? After years of standing up to intransigent industries and slow-moving bureaucracies, is he ready to take a rest and enjoy retirement? "No," he says without hesitation. "I enjoy doing something. Besides, there are still 45,000 deaths on U.S. highways each year. That's 125 a day. A lot of those deaths can be prevented. I just have to keep pushing."


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