The biggest problem is that diesel exhaust is the most damaging source of air pollution in the U.S. today. The average lifespan of a diesel engine is 29 years. Because emissions control requirements are lacking for diesel engines on the road today, they will leave a legacy of polluting our roadways and communities for decades.
strict emissions requirements for new diesel engines are being phased in, but the benefits won't accrue until at least 20 years from now.