(FORTUNE Magazine) – THERE YOU ARE, cruising blissfully down the highway. The world treated you just super this particular day, and you are murmuring the lyrics of a beloved tune playing on the car radio. Then you glance at the rearview mirror and suddenly get a serious case of the galloping jitters. Bearing down on you at horrific speed is a humongous truck, 80,000 pounds of gleaming steel. You have never felt more vulnerable. All you can do is white-knuckle the steering wheel and beseech your deity. After the truck has rumbled past, you may feel a mite silly about your reaction. You shouldn't. The number of U.S. highway accidents involving heavy trucks has rocketed in recent years (see chart). About 4,500 people died in truck accidents last year, and the odds are somewhere around 40 to 1 that car occupants rather than truck drivers will be the squashees in a collision. Says Brian O'Neill, president of the Insurance Institute for Highway Safety, a Washington, D.C., research group funded by insurance companies and sharply critical of the trucking industry: ''The more you learn about truck safety, the more frightened you become.'' The growing safety problem is a lesson in the perils of deregulation. The government largely unshackled the trucking industry from pricing rules in 1980 -- a laudable policy that contained a few serious practical bugs. Of course even after deregulation, hundreds of rules remain on the books, and better enforcement of them could improve highway safety. But unlike related industries such as railroads and airlines, trucking attracts many thousands of players. Large, well-managed companies such as Consolidated Freightways, Yellow Freight System, Roadway Services, and Overnite Transportation keep good records, police their own drivers, and stay on top of their maintenance problems. But the vast majority of truckers, mostly concerned with hustling up enough business to keep ahead of their bills, are a regulator's nightmare. The problem may be worse than it seems, since states now report truck accidents with wildly varying thoroughness. Says Gerald F. Donaldson, a trucking expert at the Center for Auto Safety, a Washington, D.C., consumer group that closely monitors truck safety standards: ''You've got some states doing a superb job. California, for example. Then you've got others like Arkansas with drool on their chin.'' Deregulation compounded the problems by creating economic circumstances that made trucking far more dangerous. Price competition forced hundreds of large and medium-size companies out of business. The smaller outfits and independent owner-operators that took their place are nimbler, but these new entrants have a hard time making money. A new truck cab can cost up to $80,000. Highway taxes run $10,000 or more annually for each vehicle, and insurance will add at least $9,000 or $10,000 more. Banks demand the highest interest rates before lending money to these risky operations. Then there's fuel; big trucks get maybe five miles per gallon. To stay in business, the small operator must run each rig at least 120,000 miles a year -- more than 300 miles every day -- and hope to bring in revenues of at least a dollar a mile. In today's competitive climate, the numbers often do not add up. According to the American Trucking Association, a third of U.S. trucking companies are losing money. Result: Many hard-pressed truckers have plenty of incentive to spend excessive hours at the wheel and to overlook expensive maintenance requirements. According to some industry experts, as many as one in three long-haul drivers resort to illegal drugs to help cope with grueling hours on the road. ''Drivers can buy drugs at some big truck stops the way you buy candy in a machine,'' says Donaldson. The drug of choice: amphetamines, ''pocket rockets'' in truckers' argot. Marijuana runs a close second. EVEN A DRUG-FREE DRIVER may be a menace on the highway because of the sorry condition of his vehicle. Roadside inspections conducted in various states in the past year regularly turned up serious problems in 30% to 40% of trucks pulled over. Inspectors raise those percentages by targeting the more unsightly vehicles they see passing; on the other hand, drivers of many poorly maintained trucks avoid inspections by laying up in a truck stop when they hear of a crackdown up the road over their CB radios. When the CBers say the coast is clear, the wary truckers move on. The most common -- and most serious -- safety violations are slick tires and faulty brakes. The popular notion that a truck's air brakes enable it to stop on a dime is a myth. Even with its braking system in perfect order, a heavy truck eats up far more pavement coming to a stop than an automobile going the same speed. The sheer size of some new trucks can make them hazardous no matter how impeccably they are maintained. More rigs with double and even triple trailers now hog the road. Cab included, these behemoths can measure over 120 feet in length. According to a new study by the Insurance Institute for Highway Safety, trucks with double trailers are two to three times more likely to be in crashes than those with a single trailer. The width of some new trucks can be a danger as well. The law permits trucks to be 102 inches wide, wheel to wheel. By the time mirrors and other devices are attached, the vehicle may be 134 inches, or more than 11 feet, from side to side. Not a severe problem on an interstate with 12-foot lanes perhaps, but many secondary roads have lanes of 11 feet or less. Pity the poor driver who strays near the center line when one of these widebodies blasts by. The longer, wider trucks may be more dangerous than statistics indicate. Donaldson of the Center for Auto Safety contends the ''intimidation factor'' does not show up in accident records. No one knows how many cars a year run off the road or veer into oncoming traffic because they were shying away from an outsize truck. Donaldson has published a study demonstrating that in some circumstances a passenger car cannot safely pass one of these longer vehicles on two-lane roads. He also argues that hulking trucks are more likely to jackknife out of control for structural reasons. When a lengthy vehicle is forced to come to a sudden stop, its rear end is more likely to swing around in a kind of ''crack the whip'' effect. Some trucks are top-heavy and especially vulnerable to rolling over on highway exit ramps. Many of these ramps are designed as a spiral with a decreasing radius, and an improperly loaded trailer cannot negotiate the last turn without tipping. ''Compared to any other vehicle on the highway, the truck is basically a very primitive device,'' he says. ''You've got very poor brakes and very poor stability. When you make trucks larger, you simply exacerbate all the problems.'' INDUSTRY EXECUTIVES emphasize the economic advantages of bigger rigs and question reports calling them unsafe. They also argue that truckers have been taking a bad rap from the police and the press. Says Thomas Donohue, president of the American Trucking Association: ''So a trucker is going down the road at 52 miles an hour, and some smart-ass kid with three of his buddies crammed into a Pinto screeches to a stop right in front of him -- and boom. Who's wrong? The truck, that's who. It's big! It's noisy! It killed those children!'' Even ardent free-marketers who support trucking's deregulation would agree that government has a legitimate role in keeping highways safe -- just as it continues to regulate air safety after deregulating airline prices. Congress, seeking to counter some trucking problems it unintentionally created, passed legislation last year to better police drivers. The key provision will require all truckers to pass uniform written and road tests. Now anyone with a passenger car license may drive a truck in 20 states. In addition, many drivers hold seven or eight different state licenses -- strictly for convenience, not necessity. If a trucker piles up too many violations on his Alabama license, he just flashes Smoky the Montana card next time he gets waved over. Under the new law, a central data bank will keep track of licenses and violations in all states. The law will also stiffen penalties for truckers caught driving under the influence of drugs or alcohol and provide more funds to the states for roadside inspections. For all its noble intentions, the legislation will not provide a quick fix. The Transportation Department is not required to come up with standards for driver testing until July 1988, and the states need not start testing until 1993. In addition, the new law says nothing about long or wide trucks. Far from cracking down, Congress is likely to ease restrictions on double and triple trailers. Some industry critics contend that the new law does not do enough to ensure that drivers are well rested before they take the wheel. All drivers are currently required to keep a log of their driving time and be ready to show it if stopped for a violation. But among independents and some smaller, poorly managed companies, these records are routinely falsified; drivers commonly refer to their logs as ''comic books.'' Brian O'Neill of the Insurance Institute for Highway Safety has offered a solution: placing recording devices called tachographs in all long-haul trucks. Neither the industry nor government regulators have shown much enthusiasm for this notion, nor have they come up with an alternative that would effectively monitor drivers' hours behind the wheel. O'Neill argues for much larger fines and more suspensions for truckers who are habitually cited for traffic violations or shoddy maintenance. Because truckers may only get a wrist slap now, he reasons, they have an economic incentive to drive more hours than they should and cheat on essential maintenance. Truck safety probably will not improve markedly for some time. The industry's economic woes continue to build. Most trucking companies will still feel pressure to work drivers too many hours and put off maintenance. None of the marginal operators will invest in costly new equipment, which could provide better braking power or more stability, unless they have to. As Thomas Donohue puts it: ''We should be looking at new technology and better-designed trucks, but we've also got to deal with a brutal economic situation.'' TRUE ENOUGH, but you probably won't be pondering the industry's economic dilemma next time you feel menaced by a truck on the highway. You'll more likely be wondering how many hours the driver has been behind the wheel. You may be hoping that he hasn't popped a little something to keep awake and that the brakes on his rig still have a few miles left in them -- or that you haven't run out of luck.

CHART: NOT AVAILABLE CREDIT: SOURCE: AMERICAN TRUCKING ASSOCIATION. ILLUSTRATION BY BOB SCOTT CAPTION: The crunch of deregulated competition has led truckers to cut costs by forcing many more years of service from their rigs. Accidents involving death, injury, or damage over $2,000 are counted here. DESCRIPTION: Two charts: Number of truck accidents, 1980-1986; Truck age, 1980-1986; illustration of two trucks.