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The Safe System approach to road safety implies the goal of removing fatal and serious injury crashes from our road network.

This review addresses:

• alternative ways of classifying roads in relation to speed, across the road network, compatible with the Safe System approach
• how speed relates to crashes, fuel consumption and emissions
• the values currently placed on the costs of serious and fatal crashes, travel time and fuel savings in the developed world
• how on a macroscopic scale these values can be translated into greenhouse gas emissions savings
• how these values relate in the cost–benefit analysis context under a Safe System approach to speed.

Well attested relationships were found between speed and crashes. Safe System road types related to the maximum speeds above which serious or fatal injury would occur in various types of crashes.

Internationally, valuation of crashes is mainly based on willingness-to-pay criteria. The values placed on time are constant unit values which is a less conservative approach as there are strong grounds for sometimes discounting the values of small time periods. Macroscopic fuel savings can be linked to greenhouse gas emissions with costs expressed as unit values per kilogram of emissions.

Keywords: emission greenhouse, road, safe, safety, speed, system, time, travel, value