How Highway Closures Are Wearing Out Local Roads

We have all been there: a highway closure due to an earthquake, flood, or storm, and suddenly, our usual commute turns into a maze of unfamiliar local roads. While emergency crews scramble to repair the primary route, what often goes unnoticed is the silent, significant damage accumulating on these alternative paths.

This is not just about inconvenience; it is a hidden cost, a financial strain, and a looming threat to our infrastructure. These secondary roads, not designed to bear the heavy burden of diverted traffic, bear the brunt of the chaos, accelerating their deterioration and incurring unforeseen maintenance costs.

But what if we could quantify this unseen toll and prepare our road networks for the inevitable detours that lie ahead?

A research paper published in the International Journal of Disaster Risk Reduction entitled “Quantifying road criticality through the impact of disruptions on pavement deterioration and agency maintenance costs” proposes a methodology for measuring road criticality by evaluating how highway disruptions affect the resurfacing needs and remaining lifespan of alternative routes.

The paper by Eduardo Allen and his supervisors from the University of Auckland’s Department of Civil and Environmental Engineering, Seosamh Costello and Theuns Henning, proposed a methodology to quantify road criticality based on the impact on alternative routes.

This involved systematically removing individual road links from the leading highway network to evaluate the overall consequences on the remaining roads. The method incorporates traffic flow analysis, deterioration modelling, and economic assessment of direct maintenance costs. The authors applied this methodology to a case study of the road networks in New Zealand’s South Island.

So, what is road criticality? In this paper, road criticality refers to the potential consequences that a road disruption might produce on alternative roads. For instance, a more critical road would produce larger consequences if disrupted.

A key factor that influences road criticality is network redundancy. Redundancy means that a road network has alternative routes, which is both critical and beneficial for road users during road disruptions.

According to studies, increasing road redundancy, or the number of independent routes connecting two points, can drastically reduce network disruption. Additionally, several studies emphasise that road redundancy is essential for a successful post-disaster recovery plan.

South Island, New Zealand: A case study

This paper focuses on the South Island of New Zealand as a case study, highlighting the vulnerability of its road network to costly disruptions caused by various natural hazard events.

Notable examples include the 2010 Christchurch earthquake, which damaged 330 kilometres of roads to varying degrees, and the 2016 Kaikoura earthquake, which resulted in the closure of State Highway 1 and incurred costs of approximately NZ$465 million for the country. The case study examines road networks spanning 11,814 km, divided into State Highways and Local Roads, comprising 42.14% and 57.86% of the total network, respectively.

The findings show that local roads are particularly vulnerable when traffic is diverted from highways. In extreme cases, the monthly maintenance costs for local roads increased by as much as 289%. Additionally, pavement life on local roads suffered more than on state highways, with an average reduction of nearly 16% on local roads compared to less than 7% on state highways.

This discrepancy arises because local roads are not designed to accommodate higher traffic volumes and typically have less robust or thinner pavement structures than state highways.

Significance of the study and findings

This paper emphasises that the proposed methodology for quantifying road criticality offers transportation agencies a valuable tool for estimating the impacts of road disruptions caused by natural disasters or other events.

By understanding how diverting traffic from highways to local roads affects the system, agencies can identify which roads are most critical to the system. For instance, if a specific local road is expected to experience increased traffic due to a highway closure, road agencies can prioritise maintenance and resilience investments on these local roads instead of waiting for damage to occur.

This proactive approach allows transportation agencies and decision-makers to allocate resources more effectively, ensuring the preservation of critical road links and minimising disruptions.

Read the paper to learn more. Visit the link below.