Consider these recent findings:
American Heart Association: "Diesel Exhaust Associated with Higher Heart Attack, Stroke Risk in Men"
Reuters: "Diesel Fumes Can Affect Your Brain, Scientists Say"
New York Times: "Soot Particles Strongly Tied to Lung Cancer"
EPA Report:
"...long-term (i.e., chronic) inhalation exposure is likely to pose a lung cancer hazard to humans..."