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The Debate: Will lower speed limits reduce road deaths? A safety campaigner vs a psychologist

After a series of tragic deaths, the Government’s speed limit review group has recommended lower limits on all Irish roads. Will it be effective?

The Debate

Mairéad Forysthe: Yes. Research shows speed is accountable for about a third of fatal collisions

The Road Safety Authority’s (RSA) most recent research on road deaths bears out the fatal effect of higher speeds. This is backed by international evidence that speed is accountable for about a third of fatal collisions. And it’s not just deaths: the RSA research also points out that the number of serious injuries was nearly 10 times that of road deaths, many of them occurring in urban 50km/h speed limit zones.

The Government’s speed limit review group has recommended lowering speed limits across all national roads: from 100km/h to 80km/h on secondary roads: from 80km/h to 60km/h on rural roads; and from 50km/h to 30km/h in urban areas. It recommended an even lower speed limit of 20km/h in pedestrian zones and shared space in urban settings.

In the view of the campaign I represent, Love 30 – a national alliance of walking groups, cycling campaigners, health organisations, supporters of children’s right to walk and play, and others – this proposal is a vital part in tackling the catastrophic effects of road deaths and injuries. And it will work, provided it is accompanied by associated measures that encourage and enforce compliance.

The UN Global Ministerial Conference on Road Safety in Stockholm in 2020 described international road deaths as a “preventable epidemic” and particularly urged a “focus on speed management”, with particular emphasis on “30km/h in areas where vulnerable road users and vehicles mix”. In February 2020, Ireland was one of the countries that agreed to adopt the Stockholm Declaration on road safety, including a commitment to 30km/h in areas where vehicles and vulnerable road users mix.


Speed limits of 30km/h have become commonplace in towns and cities across Europe, with whole countries now implementing or considering them. In Spain and the Netherlands, 30km/h is the default speed on single-lane urban roads and Wales recently adopted a 20mph (32km/h) national default speed limit for urban roads. Towns and cities that have introduced 30km/h limits have seen a reduction in deaths and injuries. Edinburgh, for example, has experienced a 38 per cent reduction in casualties since it introduced wide-area 20mph speed limits in 2016.

Towns and cities that have introduced 30km/h have seen a reduction in deaths and injuries

Apart from improved road safety, reducing speed limits in built-up areas creates quieter, cleaner and safer streets that are not dominated by fast-moving traffic. This leads to increased levels of walking and cycling, and ultimately better health outcomes and reduced emissions. Our towns will become more liveable and children in particular will have more freedom to move about.

Of course, enacting legislation and bylaws, and the erection of signs, will not achieve the desired effect of reducing driving speeds in isolation from other measures. The speed limit review that was presented to the Government recommends education, training, public engagement and communications. These are critical. Ultimately, we need to change our driving culture to take account of all road users. Speed limits are recognised as a necessary safety precaution on our roads to counteract the tendency of many drivers to exceed safe driving speeds. We need to educate all drivers to observe speed limits and to drive at speeds appropriate to the driving and road conditions.

Enforcement is also vital. Present compliance with speed limits here in Ireland is fitful at best, as shown by data from the RSA’s regular Free Speed surveys. Motorists should expect to be caught, and penalised, if and when they exceed speed limits.

Reduced speed limits also need to be accompanied by measures such as engineering improvements, average speed cameras, number plate recognition, as well as technological development in vehicles. In countries such as France and the Netherlands, traffic-calming is commonplace on the approach to low speed zones and can include measures such as chicanes, street trees and planters. Love 30 also supports the proposals to reduce speed limits on local roads and on national secondary roads. Local roads are not suitable for 80km/h speeds, which are a danger and a deterrent to people walking and cycling on these roads.

We believe that the proposed reductions in speed limits, properly implemented, can reduce speed on our roads with a consequential reduction in deaths and injuries.

Mairéad Forsythe is a committee member of Love 30, a national alliance of individuals and organisations in Ireland campaigning for lower speed limits in urban areas

Dr Mick O’Connell: No. There has to be some trade-off between population safety and population mobility

Ireland has made great progress towards safer road travel. Eurostat figures indicate that the number of cars per 1,000 people doubled between 1990 and 2020, while road fatalities steadily declined in that period from 415 (1992), 376 (2002), 163 (2012) and 155 (2022).

However in recent years, there has been a plateauing in this improvement. Accompanied by a number of recent well-publicised tragedies on Irish roads, it is understandable that there is pressure on Government to act.

Road safety is a function of a number of factors such as road quality, vehicle design and traffic volume. But driver behaviour is also key. Those who support a reduction in speed limits across a number of road categories argue that they would act as a regulatory lever in nudging driver behaviour towards safer driving. However, when dealing with complex behaviours, even the best-intentioned policies can have unintended negative consequences.

What might we reasonably expect if broad reductions in speed limits were introduced in Ireland?

Two Government-sponsored reports looked at key outcomes – the Transport Infrastructure Ireland (TII) report of 2022 (focusing on National Roads), and the AECOM report of 2023. On carbon emissions, speed limit changes would make minimal differences, as cars emit most at low speeds, according to TII 2022. In terms of economic cost, the increase in journey time costs was estimated at up to a maximum of €3.8 billion over 30 years.

The introduction of speed limits perceived as painfully slow or pointless will require very heavy policing, and could create widespread public noncompliance

But what about the outcomes of most concern – collisions and fatalities? The TII forecast an additional 29-217 collisions a year, resulting in five to 35 more fatalities a year.

This seems counterintuitive: why would a speed limit reduction produce more collisions and fatalities? This is because of the phenomenon of traffic rerouting. Facing speed limit reductions on larger roads with lower collision rates, motorists are likely to reroute to more direct but less safe roads with higher collision rates. The AECOM report notes that “the potential for this rerouting has increased in recent years with navigation guidance becoming ubiquitous on mobile phone devices”.

This is supported by a natural experiment reported in a Queen’s University Belfast study, where a decrease to a speed limit of 20mph (32km/h) over three years in 76 Belfast streets found no significant impact on collisions or casualties.

Given that the research is not pointing towards improved safety – in fact, it points towards possible negative effects – the Government should pause before acting. Is it possible that in many road collisions in Ireland, the issue is not that the driver is complying with a too-high speed limit, but rather is significantly exceeding the existing limit? Data could be gathered to answer this question relatively easily. And if collisions are principally arising from drivers exceeding the current speed limits, then why would reduction of these limits prove useful?

Motorists are not the only victims of traffic collisions. Areduction of urban speed limits from 50km/h to 30km/h would surely save the lives of some pedestrians and cyclists – but a further reduction of the speed limit from 30km/h to 10km/h would certainly save even more lives. Yet, nobody has – as of yet – proposed a 10km/h limit. Why not? Because most of us understand that there has to be some trade-off between population safety and population mobility.

Compliance requires both enforcement and consent. Traffic laws need to be seen by the public as reasonable. On a near empty urban road at 10am on a Monday, what motorist will feel that a 30km/h limit is reasonable? The introduction of speed limits perceived as painfully slow or pointless will require very heavy policing, and could create widespread public noncompliance. Traffic regulations should still allow drivers to use some individual initiative and decision-making.

Governments need to stay responsive to road safety, but must avoid knee-jerk reactions to a small number of highly-visible tragic events. Overall, road safety has been improving in recent decades in Ireland. Before embarking on radical changes to current speeding limits, a more thorough analysis is required.

Dr Mick O’Connell is associate professor at the School of Psychology, UCD. He previously worked as a research fellow in Brunel University, on a study funded by the TRL (Transport Research Laboratory – UK), Deterring Speeding in Young Drivers.