However, like a double-edged sword, high speeds have been strongly associated with avoidable road deaths and life-changing injuries. Speeding directly accounts for about a third of fatalities in high income countries and more than half in low-and middle income countries [2].

Speed management is therefore critical for preventing deaths on our roads and needs to be supported by the setting of appropriate speed limits. However, this is a complex technical challenge, and the perceptions of what speed limits are safe and appropriate on any particular road section can be controversial. There is often conflict between road safety professionals, who will generally recommend lower speed limits than those currently in place on safety grounds, and politicians and decision makers, who may be highly influenced by the negative views expressed by some of the public.

Setting and enforcing safe speed limits is ultimately a life-saving approach that places the protection of the road user at its heart

How can we reduce travel time? How do we solve congestions in our cities? What are the travel needs of commuters? How can we keep our children safe as they leave school? These are a few of the important questions that influence approaches to prescribing speed limits. This has resulted in inconsistencies in setting speed limits across various geographies, leading to a patchwork of approaches. These apparent variations in the experiences of the public breeds mistrust and is a real barrier to improving the safety of our roads.

Setting and enforcing safe speed limits is ultimately a life-saving approach that places the protection of the road user at the heart of mobility needs. In ideal circumstances there is a sweet spot, promoting both mobility and safety. At the heart of current best practices is a philosophy described as the Safe System approach. This provides guidance that supports the setting of safe traffic speeds that seek to protect all road users from harm.

The Safe System approach states that no aspect of the safety of the road system should be compromised for greater mobility [3]. With this basis at its core, speed limits (and therefore maximum traffic speeds) are set through a Safe System approach in the context of the possible collision types that can occur on a road section. The logic behind setting safe speeds is rooted in physics. Vehicle speeds strongly influence the likelihood of a crash occurring and, in the event of a crash, the severity of the injuries suffered by the victims.

The complexities of the interplay between speed, journey time and risk therefore demands a scientific, evidence-based and consistent approach that considers the unique characteristics of each road section.

TRL has produced a Speed Management and Assessment Tool (SMAT) which systematically manages speed across networks and on specific stretches [4] of roads. It is a risk-based approach which determines the appropriateness of existing speed limits by assessing the level of safety provided by the road characteristics present and how these impact the likelihood of various potential collision types. It requires data on current traffic speeds, speed limits, traffic volume, road characteristics, number of lanes, driveways and traffic signals. The tool takes iRAP coding data and repurposes it to help stakeholders in a robust intelligence-led approach to defining Safe System speed limits without the need for additional data collection. The SMAT can also be used to understand where traffic speeds are in conflict with these limits.

It supports road authorities and key stakeholders by providing simple but powerful information to support with understanding what the recommended speed limits on road sections should be. It can help inform decision-makers with making evidence-based decisions to manage vehicle speeds and, ultimately, improve road safety. With the kind permission of National Highways, who supported the development of this tool, TRL has successfully applied the tool in Low- and Middle-Income Countries (LMICs), such as Ghana and Nepal, where speed management is critical, yet access to data is limited.

Setting appropriate speed limits with consideration to the different levels of vulnerability and road resilience provide a clear pathway towards reducing or eliminating the severe outcomes of road crashes. It is imperative for all professional, decision makers and road users to work towards safer speeds in a harmonised and evidence-led manner.

TRL’s Nancy Abira, Angela Fuller-Dapaah, Linda Masibo and John Fletcher wrote this blog for Road Safety Week 2023. Sign up to join the national conversation about speed.

References Down arrow icon to open accordion
  1. Kamba et al. (2007) Why Do People Use Their Cars: A Case Study in Malaysia Microsoft Word - 520b-ajas to jss.doc (
  2. WHO (2018) Global Status Report on Road Safety. World Health Organization. Geneva.
  3. Tingvall C, Haworth N. (1999) Vision Zero - An ethical approach to safety and mobility. 6th ITE International Conference Road Safety & Traffic Enforcement: Beyond 2000; Melbourne. Available at:
  4. TRL (2022) Study to determine the scalability and efficacy of a Speed Management and Assessment Tool (SMAT) to Low- and Middle-Income Countries (LMICs)

Nancy Abira, Safety consultant

Nancy is an engineer with 12 years’ experience in highway engineering, transportation, and road safety. She has worked on establishing road safety management systems and institutions in Kenya, Uganda, and Bangladesh and on projects including establishing the institutional framework for road safety management, development of road safety manuals, road safety engineering, speed management and crash database management. She currently sits as an alumni trainer and contributor to the Delft Road Safety Course (Netherlands). She is an experienced Road Safety Auditor and registered with the engineers board of Kenya.

Angela Fuller-Dapaah, Safety consultant

Angela holds an MSc in Transport Planning from the Institute of Transport Studies, University of Leeds (UK). She is a transport planner with demonstrated experience in road safety and speed management. She has worked with international institutions and road safety stakeholders in Ghana to prepare road safety plans, evaluate transport strategies, conduct feasibility studies, and undertake risk assessment of vulnerable road users. She is a member of the Global Youth Coalition for Road Safety.

Linda Masibo, Safety consultant

Linda holds a degree in Civil Engineering and a Master of Transportation Sciences, Road Safety in the Global South. She works towards safer roads in her work. Additionally, she advocates for safe and sustainable mobility. Linda has worked in Kenya, Uganda, Ethiopia and in Belgium and brings a particular interest in road safety education to her role as a road safety consultant at TRL.

John Fletcher, Practice lead, international safety

John has more than 28 years of experience focusing on improving road safety in the UK and in more than 30 countries globally. John is head of the TRL iRAP Centre of Excellence and is on the iRAP Global Technical Committee board. John has been TRL's representative to the United Nations Road Safety Collaboration (UNRSC) and the International Road Accident Database Group (IRTAD).

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