This report of case studies on the topic of speed limits includes a series of implemented countermeasures or experimental proofs of concept to help improve the road safety in a specific location or area.

PIARC didn´t work on specific speed issues in the past periods, therefore this report also contains a short theoretical introduction concerning the role of speed in road safety and the importance to set speed limits that are credible for road users. Credible is in general an individual task and influenced by drivers’ culture and acceptance. Within the Road System and Administration, the task of ‘setting credible speed limits’ remains therefore to be a highly sophisticated and multi-responsible procedure. The focus for Road Operators and Administrations is to provide safe speeds by design of the road system (road, environment and operation) that reduce crash risks and/or severity. A concept of ‘Hierarchy of Control’ within treatments is strongly recommended.

Roles and responsibilities in setting speed limits are different in countries and areas. There are different approaches for road design and roads in operation. Therefore, no general suitable rule and procedure can be offered, but a look at examples from best performing road administrations might help.

The case studies received are from all over the world. The collection of case studies represents an important step toward the construction of knowledge and should help road authorities and engineers to find helping solutions in their work to set credible speed limits. This PIARC document contains the description of a set of interventions in the stage of design, implementation and operation.

The analysis of the case studies puts in evidence that the effectiveness of a specific case study will vary according to the local conditions, driving habits, traffic rules, regulations and/or signing and marking standards. A countermeasure that seems to poorly impact road safety in a specific region, may demonstrate a better impact in other regions with different conditions (not only because of the road and its environment, but also because of cultural aspects).