Conclusion: challenges for the future

The title "Challenges for the Future" implies the challenge to summarize a very complex meeting. Of necessity, I will present a personal impression. My interest is in risk assessment, which I define as a process for summarizing science in support of decision making. Risk assessment is sometimes regarded as arcane numerology, a rigid process of computing risk numbers in which much available science is unused. I am a strong advocate for the broader definition of risk assessment. It is encouraging to learn how much science is becoming available for use in risk assessment for gasoline, its components, and alternative fuels.