Aerial shot of M17/M18, showing a flyover and roundabout, with fields alongside the road.; Aerial shot of M17/M18, showing a flyover and roundabout, with fields alongside the road.;

TII Analytic Pavement Design Method, Ireland

How can optimising road design accelerate Ireland’s journey to net zero?

What does it mean to optimise a road? Is it possible to reduce a road’s carbon footprint and lessen the carbon and economic costs across the asset’s lifecycle? There are many ways to make road use more efficient – planning and placement, multi-modal design, but what about the design of the road itself?

The materials used in pavement design – concrete, asphalt, gravel and soil – make up the largest proportion of carbon emissions related to the construction and management of roads. Our circular economy and road pavement design specialists have been working with Transport Infrastructure Ireland (TII) to explore innovation opportunities in road design, inspired by circular economy principles.

Arup has worked with TII to develop a design procedure, in collaboration with industry partners. Transitioning from historical empirical design methods, which are inherently conservative, to a materials performance approach, which takes advantage of more detailed pavement modelling allied with an increase in digital data management capacity, harnesses the inherent properties of the materials to a greater extent within the design process. Intervening early in the pavement materials design process enables a significant reduction in carbon impact, construction waste and long-term expense for a road.

TII and Arup ran a case study on 15km of National Road dual carriageway, helping to reduce bituminous materials by 8% and reducing embodied carbon emissions by more than 450,000kgCO2e.

Project Summary

15km case study

8%bituminous material quantity reduction

>450,000kgCO₂eembodied carbon emissions reduction

Pavement: innovative performance-based design

When TII set out to determine a way to optimise the vast network of roads across the country, they first questioned the potential to innovate road design fundamentally.

Since the 1950s, road design in Europe has relied primarily on empirical methods that provided a reliable solution to historical challenges – mainly limited by computing methods and the complexity of modelling pavement structure and materials. The old method relies on a limited number of design factors, including significantly lower historic traffic levels.

Updating the pavement design methodology presents two opportunities: firstly, it makes modern analytical methods available to designers, and secondly, it takes into account the greater level of detail available about material performance characteristics. Using this updated methodology will reduce material consumption and carbon impact of designing new roads and repairing existing ones.

By planning for reuse from day one, designers can minimise the materials required, select the optimal material make-up and reduce the environmental impact, asset lifecycle costs and construction effort, creating not only the roads of today, but the roads of the future. ” Janet Lynch Janet Lynch Associate

Road design and the circular economy

Building off the layers-based approach to infrastructure design, which focuses on the inter-connectedness of an asset’s elements, this design method developed by TII and Arup looks in detail at choosing the correct materials for road design by taking a performance-based approach.

The design method developed by TII and Arup looks in detail at choosing the correct materials for road design by taking a performance-based approach.

Designing for longevity has always been a core aim for road infrastructure.

Taking a materials performance-based approach enables the assessment and use of new and innovative materials. It also allows designers to specify and use only the necessary amount of each relevant material for specific road conditions and contexts, as well as introducing the opportunity to design for reuse.

The result is a significant reduction in construction waste and cost, and, ultimately, carbon footprint of roads.

Tomorrow’s roads: digital asset management

Arup’s transport experts worked closely with TII to ensure that TII’s newly developed tool to accompany the analytic pavement design method enables an asset’s data flow to be tracked throughout its lifecycle.

Materials data is inputted to TII’s web-based software, allowing for iterative design testing and helping designers to consider multiple impact factors. These take into account material performance characteristics, as well as other critical factors such as traffic load patterns, pavement structure and layer thickness, environmental and ground conditions and performance risk.

Having a digital record of the materials used in all road designs will help TII to improve monitoring, optimise costs and predict maintenance requirements.