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Navigating the challenges of divided road implementation

Many sections of Ireland’s national road network are reaching a crossroads. As traffic patterns, technology and policy evolve, road authorities must decide how best to extract greater safety and value from existing roads rather than rely on wholesale upgrades or replacements.

How can we increase the safety of our most at‑risk rural routes while balancing access, environment and community needs? John Shalloe, Mark Condron and Rowan O'Callaghan, our road safety specialists, review the case for divided roads, speed management and pragmatic engineering interventions, and outline the technical, planning and stakeholder considerations that will determine successful delivery.

John Shalloe Mark Condron Rowan O'Callaghan

Infrastructure

Ireland

We have been involved in many initiatives to improve road safety in Ireland and have successfully implemented a number of these in conjunction with Transport Infrastructure Ireland (TII) and Local Authorities.

This experience goes as far back as the National Roads Needs Study in 1998, which was the foundation for our major inter-urban road network, heralding major road safety benefits by dramatically reducing road collisions, increasing road worthiness, and improving transport efficiency.

As today’s focus shifts towards maximising the value of existing road assets rather than upgrading or replacing them, this requires novel approaches to maintaining a safe road network. This has now become a pressing concern for our road authorities, due to increasing rates of road deaths year on year since 2021. This is particularly prevalent on single carriageway rural roads, which are statistically the most dangerous due to the inherent risk of head-on collisions and run-off-road accidents.

National approach

The Department of Transport initiated a National Speed Limit Review in 2023 to look at the appropriateness of speed limits across the entire road network, and this resulted in a four-phase implementation plan:

Phase 1 - Reduce the default speed limit on rural local roads from 80km/h to 60km/h.
Phase 2 - Introduce a 30km/h default speed limit in built-up and urban areas.
Phase 3 - Reduce the default speed limit on national secondary roads from 100km/h to 80km/h.
Phase 4 - Reduce speed limits on roads adjacent to schools in rural areas.

Phase 1 came into effect on 7th February 2025, and resulted in approximately 83,000km of Ireland’s road network being subject to a lower speed limit. The effects of this will take time to assess.

Phase 2 is currently underway, with an implementation date of 31st March 2027. This should see a reduction in vulnerable user related collisions, but enforcement will be critical to its success.

Timelines have not yet been set for implementing Phase 3 and 4, however preparations for their enactment are already underway, particularly on Phase 3 where the Road Traffic Act 2024 has made legislative provision for a change from 100km/h to 80km/h on national secondary roads.

While the default position for national secondary roads is a blanket reduction in speed limit to 80km/h, the 2023 Review does make some promising recommendations on implementing divided roads for any new section of rural road upgrade, and for investigating the conversion of existing rural roads into divided roads, where it is appropriate and necessary to maintain the higher speed limit.

This is an important factor as a speed limit reduction itself without physical intervention to divide or calm traffic, may not result in the anticipated reduction in road collisions. The outcomes of the implementation of Phases 1, 2 and 3 above will be interesting in that regard.

The concept of providing a divided road is set out in EU Regulation 1315 / 2013 and relates to the Trans-European Transport Network.

The 2023 Review draws on this requirement along with enhanced pedestrian and cyclist segregation, as the means by which 100km/h speed limits can be retained.

With approximately 4,000km of the national road network as single carriageway, of which approximately 2,650km is national secondary, a significant part of the road network will be affected by these decisions. How much of the network should reduce to 80km/h, and how much merits consideration to retain at 100km/h? To attempt to answer this, we first need to look at the various means to divide roads, and the potential effects on the surrounding environment.

Methods to divide roads

The design standards in Ireland set out three types of divided road, as distinct from motorways:

Type 1 Dual Carriageway

Similar to motorway standard, with hard shoulders and a concrete median barrier

Type 2 Divided Road

2+2 lane configuration divided by a safety barrier, with no hard shoulder

Type 3 Divided Road

2+1 lane configuration divided by a safety barrier, with no hard shoulder

In retrofit scenarios such as improving safety, Type 3 is the least impactful in terms of space required. However, requiring a paved area width of 13m before considering segregated facilities for vulnerable users, it is difficult to see how this could be implemented on a widespread basis on the national secondary network, without significant impact to landowners and major roadside hedgerow loss.

Divided road pilot schemes are underway on parts of the national primary network that are single carriageway. On the N5 at Swinford, we are investigating solutions for improving safety on a section of the existing bypass which has a high collision rate, but with a wider cross section available, feasible solutions are immeasurably easier to implement.

Key challenges

Despite the clear benefits of divided roads, several challenges hinder its widespread adoption on existing roads. Firstly, the presence of junctions and private entrances along rural sections of national road complicate the design and implementation of divided road systems.

The need to maintain access for local traffic while ensuring safety and the inclusion of overtaking sections can lead to conflicts in design priorities. Some accesses may become ‘left-in and left-out only’ due to the presence of a median barrier.

Additionally, overtaking sections are recommended to be at least 2km long. This means that junctions which facilitate U-turn manoeuvres are spaced a minimum of 2km apart, which may add to the journey time of local residents.

Limited space in rural areas also poses a significant constraint. Many existing single carriageway roads were not designed with the additional width required for a divided road, making it difficult to accommodate the necessary infrastructure without extensive land acquisition.

Other challenges to consider when dividing existing roads include:

Cost: The financial implication of converting an existing single carriageway road into a divided road will be substantial.

Access disruption: Dividing a road means altering many accesses and junctions, which can often restrict the movements of road users and a perceived loss of facility.

Community opposition: Local communities may oppose changes due to concerns about personal property / access loss, increased noise, pollution, traffic speeds.

Land acquisition: Widening roads requires additional land acquisition, which can be legally and logistically complex and costly.

Environmental impact: Construction activity due to road widening will disrupt local ecosystems (established hedgerows, drainage ditches etc.) and require environmental assessments. Additionally, the environmental impact of diverting and re-routing traffic arising from a median barrier will increase journey times and therefore carbon emissions.

Alternative solutions

To address the challenges in making these roads safer, a multifaceted approach is essential. Innovative design solutions are needed to maximise the use of available space. For example, it may be feasible to integrate narrow medians or flexible barriers into existing roadways, allowing for a divided road configuration without significant land acquisition.

The use of technology such as automated traffic management systems, can also help optimise traffic flow at junctions and private entrances, minimising disruptions while enhancing safety. Various trials are underway in the UK and other jurisdictions looking at the use of Vehicle Activated Signs (VAS) and Radar Technology to detect hidden hazards.

Other possible alternatives include:

Central median barriers: Installing physical barriers such as concrete or steel guardrails to separate opposing lanes, without strict adherence to the cross-section requirements of Type 2 or 3 Divided Roads.
Road duplication: Converting single carriageway roads into dual carriageways by constructing a second carriageway adjacent to the existing one. Allowing potential to retain existing boundaries / hedgerows in between.
Flexible posts: Installing flexible posts or bollards along the centreline to provide a visual and partial physical deterrent.
Vegetated medians: Creating landscaped medians with shrubs or trees to separate lanes, to provide a visual and partial physical deterrent, while also enhancing aesthetics.
Physical delineation: Use of raised road markings and/or raised delineation devices to create a visual separation between lanes.

With a key requirement being to physically separate opposing traffic lanes, some of the above solutions may only offer limited safety benefit.

Bollards And Vegetated Median — Example of flexible posts and vegetated medians

International best practice

Globally, several countries have successfully implemented divided road systems, demonstrating their effectiveness in improving road safety.

In the United States, the Federal Highway Administration has promoted the use of median barriers on rural highways, which have been shown to reduce fatal collisions by up to 50%. Similarly, Australia has adopted a comprehensive approach to divided roads, incorporating wide medians and clear zone policies that allow for safer vehicle recovery in the event of a collision.

In Europe, countries like Sweden and the Netherlands have embraced the Vision Zero initiative, which aims to eliminate fatalities and serious injuries on the road. This approach has led to the implementation of divided roads with innovative design features, such as flexible median barriers and improved signage, which contribute to a safer driving environment.

The integration of technology, such as intelligent transport systems (ITS) has also been a key component in enhancing the safety and efficiency of divided roads.

Summary

While challenges such as junction design, space limitations, cost, and environmental impact exist, innovative solutions and collaborative approaches can pave the way for successful implementation of divided roads. The lives of road users depend on it.

Engaging stakeholders early in the planning process is crucial for addressing concerns related to access and environmental impact. Conducting thorough consultations with local communities, landowners, and environmental groups can lead to more acceptable solutions that balance safety, strategic function and local need.

Ongoing research and data collection are also vital for evaluating the effectiveness of divided road systems. By analysing collision data and conducting road safety audits, road authorities can continuously refine their approaches and share best practices with other jurisdictions.

By learning from international best practices and engaging with stakeholders, road authorities can create safer road networks that meet the needs of all users while promoting sustainable transport solutions.

Key questions to consider in implementing divided roads as a solution to the National Speed Limit Review outcomes:

Does simply lowering the limit to 80km/h solve the problem of speed related collisions? Without physical separation and a lack of enforcement, how effective will this be?
Where is the demand to maintain 100km/h on single carriageway roads? We are a small island nation with shorter journey times by comparison to our European neighbours. Should we cap all single carriageways at a maximum of 80km/h?
Does the perceived need to maintain 100km/h on parts of our single carriageway network outweigh the impact of implementing divided roads?
Should the National Speed Limit Review have considered a speed limit reduction on the 1,400km of single carriageway national primary network? Is there evidence to suggest they are safer?
Is it more feasible to retrofit the single carriageway national primary network with divided roads than the national secondary network, given the typical wider nature of these roads? As solutions to the national secondary network may take longer to implement, is there a quicker return on safety benefits in the interim by adopting this approach?
Is a wider roll-out of divided roads a key solution to achieving the Irish Government’s Vision Zero, to eradicate road fatalities and serious injuries on Ireland’s roads by 2050?

Ultimately a reduction in road collisions is a key driver for implementing these initiatives, and the road safety industry has a major part to play in overcoming the challenges involved.