Blame the customer. That’s been Detroit’s response when figures show that today’s automobiles still produce 50 percent as much total pollution as in the late 1960s, despite regulatory limits that set emissions from individual vehicles 90 to 96 percent lower. The fleet of U.S. cars is still producing half as much pollution as in the pre-regulation era, because people are keeping their cars longer, driving more, and, the carmakers claim, neglecting to maintain their new ones.

We are driving about twice as many miles as before regulations were applied, but that doesn’t account for the gap. About half of all automotive emissions come from “high emitters”-vehicles with emission control systems (ECS) that have failed in use. A high emitter produces some 25 times as much pollution as a properly functioning vehicle. About 510 percent of all 5-year-old vehicles are high emitters.

ECS failures stem from a variety of causes. A good example is failure of the fuel-injection system-either failure of the injectors themselves, the computer chip that calculates the amount of fuel needed, or the sensors that provide data to the chip, such as on the amount of air flowing to the cylinders. Failure of any of these components results in incomplete combustion and poor performance of the catalytic converter.

Our research shows that ECS failures occur largely in a few vehicle models. Many of these failure-prone models are relatively new-from the early nineties. We have found other models that experience almost no such failures, re-gardless of any neglect or abuse, for at least nine years. Thus the burden for fixing the problem lies not so much with drivers as with manufacturers.

This model-dependence apparently comes as a surprise to manufacturers and regulators, partly because they receive little feedback when these systems go wrong. Existing tests and surveys turn out to be inadequate for several reasons:

The standardized emissions test for new vehicles entails aging of individual components in the laboratory rather than subjecting the whole system to the rough and tumble of real-world driving and maintenance, or lack of it.The elaborate and expensive “in-use” tests that regulators conduct include only tiny numbers of meticulously maintained vehicles of a given model. Such procedures catch few of the dirty offenders.Information from dealers on their attempts to fix emission control systems is haphazard-partly because drivers are often unaware of, or uninterested in correcting, an emissions problem.State inspection agencies rarely report failure rates by vehicle model. Plus, many state-administered “smog tests” simply sample emissions from a car while it is idling-despite the fact that cars pollute far more under normal driving conditions.

One solution is for states to undertake even more ambitious inspection and maintenance programs, as recommended by the Environmental Protection Agency. But inspection and repair of millions of vehicles is costly, cumbersome, and often done poorly. Almost no garages have the costly equipment needed to accurately measure emissions from a vehicle that is under power rather than idling. And many believe that repair efforts at thousands of garages are even less effective than the initial inspection. Automakers are installing on-board diagnostics (OBD), which notify a driver when emissions controls have failed, in all 1996 and newer cars. Regulators hope OBD will make state inspection and maintenance programs more effective.

Another approach would focus on identifying the particular vehicle models whose emission control systems are prone to fail. Doing so will require collecting data from hundreds of thousands of vehicles while they are on the road, using OBD or roadside emission sensors. Carmakers report that OBD is already identifying manufacturing flaws in particular vehicles before they reach dealers’ showrooms.

Unfortunately, there is no formal mechanism in place to make data from OBDs or from state-run emissions testing programs available to the public. Simply making public information on which models fail, as opposed to individual vehicles, might motivate car manufacturers to create more durable emission control systems. Automotive engineers have told us that if they knew about such failures, automakers could without great difficulty idenify the design or manufacturing practices that led to the flaw and correct the problem in future vehicles. If manufacturers did not take action, regulations could penalize them for models that display unacceptable rates of failure.

With more durable emission control systems, cars would re-main as clean as new for a far longer time-helping remove automobiles from their present status as the major source of air pollution.