Modelling stocks and flows of road networks - Case study of the US 1905-2015

The accumulation of materials in buildings and infrastructure in national economies has received increased attention in IE research in the context of resource efficiency, waste minimisation and low carbon development. In the... [ view full abstract ]

The accumulation of materials in buildings and infrastructure in national economies has received increased attention in IE research in the context of resource efficiency, waste minimisation and low carbon development. In the absence of data most research has relied on modelling approaches. Modelling inputs, including information on the extraction of construction minerals and information for building and infrastructure lifespan are often not very credible and data gaps pertain. 

In this research, we employ novel methods for estimating construction material flows and, using dynamic lifetime distribution models that enhance the reliability and robustness of the resulting accounts for stocks, demolition waste flows. To assess the requirements of construction minerals of the road network in the United States we develop a bottom-up stock driven model to assess long-term inflows, outflows, and materials accumulated in roads. We estimate material requirements using the expansion of the transport network as a driver, and scheduled maintenance and technological coefficients from engineering literature to assess input and output flows. We apply the model to historical data for the United States road network from 1905-2015. We show that the current material stock of construction minerals in the road network of the United States is 15.1 billion tonnes, growing 21-fold since 1905.

During the 20^th century, the material requirements of road construction have declined from 35% to 15% of economy-wide material consumption of non-metallic minerals in the United States. The share of roads in economy-wide in-use stocks has also declined from 17% to 13%. This shows that roads, once established, remain in place and the majority of material flows are due to extending and refurbishing them, while the construction of completely new roads make up a much smaller part of the material flows due to the road network.