8 Impacts Related to Route Security
Route security refers to the level of risk being carried to keep a route open to road traffic and other users. Insecurity might be caused by a number of factors:
- Inadequate maintenance regimes. For example, if major structures such as tunnels or bridges are not inspected on a sufficiently frequent basis, or if funding is unavailable to replace ageing culverts or retaining walls at risk of collapse, the risk of the route being (partially) closed for safety reasons and repairs increases.
- Environmental issues. For example, roads in mountainous terrain or unstable geological areas are at risk of slips and subsistence. Whilst investment might be able to mitigate some of the risk, it is not possible to remove the risk.
- Extreme events. Similar to environmental issues, extreme events such as unexpectedly heavy snowfall or rain might lead to closure of links or entire areas of a road network. Again, whilst design and maintenance processes aim to mitigate the effects to some degree, it is not possible to remove the risk.
The level of maintenance funding will impact on the ability of an Authority to maintain an appropriate level of route security. Activities to mitigate the risk include structural inspections, repairs and replacement, drainage cleaning and maintenance, embankment protection and river training works and winter maintenance. Winter maintenance has been excluded from this review and so the study has focused on other factors that may affect security.
The impacts of increasingly insecure networks might be related to the environment (e.g. flood defences), safety (e.g. increased accidents), quantifiable economic issues (e.g. disrupted journeys) or social issues (e.g. community severance). The qualitative risks of route security have been identified during the literature review and, where appropriate, are summarised in Section 14.1, with further details in Appendix B. The analysis reported in this Section has sought to quantify the risk of route security based on evidence from Scotland and elsewhere.
8.2.1 International and national evidence
Failure of the road network infrastructure can cause significant disruption and may reach the news headlines. In recent years in North America, there have been various high profile cases of collapsing or partially collapsing structures on major routes, where questions have been raised over the adequacy of initial designs and road maintenance strategies and funding. Examples include the Minnesota bridge collapse in 2007 which caused 13 fatalities and many more injuries, as well as other longer term impacts (National Transport Safety Board, 2007). More recently, a partially collapsed tunnel in Montreal has caused disruption and it has been reported that engineers have questioned the adequacy of the long term maintenance plans (The Canadian Press, 2011).
In the UK, weather events have also caused major disruption in recent years. For example, extreme flooding in 2009 in the Lake District caused numerous bridge closures and meant that many journeys faced major diversions (BBC News, 2009).
The impact of such events might be immediate, as noted in the above examples but there is often a longer term impact. No Authority can avoid the need to address such significant hazards to the travelling public, and so in the aftermath, funds are diverted to repairs and replacement strategies at the expense of other items in the road maintenance budget.
Whilst immediate repairs and operations due to major weather events and other such environmental impacts are usually funded from discretionary budgets, again, the longer term and less visible impacts often have to be funded out of core road maintenance budgets.
No evidence has been found of any Authority which has yet managed to objectively quantify the risk of such failures and consider the quantitative trade-offs due to the potential impacts. All evidence suggests that road Local Authorities:
- Develop inspection and maintenance regimes based on engineering experience;
- Expect to manage the risk of route security with such processes and find little opportunity for reducing such strategies when funding is constrained;
- Accept that if funding for road maintenance is constrained, significant reductions will have to be made elsewhere in the budget with only marginal savings being possible when related to route security.
8.2.2 Scottish trunk roads
A good example of route security issues was experienced on the Scottish trunk road network in Scotland in October 2007 on the A83 at Rest and Be Thankful Pass in Argyll and Bute (Transport Scotland, 2009c). A landslide occurred which closed the route for 12 days. There were no accidents and the economic impacts were assessed based only on a quantified analysis of road user disruptions (i.e. the extra time taken by road users to complete their journeys). Other economic effects on the local economy (e.g. from loss of trade) have not been assessed. Key statistics include:
- The average daily traffic at the site was around 2,250 with approximately 4% heavy vehicles
- The route was closed and only opened partially late in the 12 day period
- The diversion route was estimated to be an additional 41km with an average additional journey time of 34 minutes
- The economic impact has been estimated (at 2008 prices) as £320,000 which is the central estimate of a range which might vary between £180,000 and £620,000 depending on assumptions of how many trips were actually diverted rather than cancelled or deferred until the road re-opened
- If the event had happened during the peak tourist season (summer), the central estimate would increase to £540,000 due to increased traffic levels.
At 2002 prices the central estimate of the impact is £272,000. Table 8.1 shows the impact if some of the key assumptions are varied.
Note that the data makes no assumptions around the impact of different maintenance regimes as the event was an unforeseen environmental impact. If consideration was being given to the effect of different maintenance regimes (i.e. funding more maintenance to reduce the potential occurrence of an event) then the agency costs for prevention would increase but could be offset against the anticipated reduction in economic impact.
Table 8.1 Scenarios for route security (2002 prices)
Low traffic rural road (ADT 2,250) with significant diversion (34 minutes) for a reasonable period of time (12 days) (e.g. landslide)
High traffic short delay1
High traffic rural road (ADT 20,000) with medium diversion (15 minutes) for a longer period of time (30 days) (e.g. large geotechnical failure)
Low traffic long delay1
Low traffic rural road (AADF 2,250) with significant diversion (34 minutes) for a long period of time (1 year) (e.g. bridge failure)
Medium traffic long delay1
Medium traffic rural road (AADF 10,000) with medium diversion (15 minutes) for reasonable period of time (12 days)
Note: 1. These impacts assume durations of disturbance but, in practice, temporary alternative routes may be put in place to reduce the impact (e.g. temporary bridge erected when a bridge was destroyed by flooding in Cumbria, in 2009).
Source: A83 Rest and Be Thankful closure
8.2.3 Scottish local roads
The trunk road network represents the strategic arterial routes and is therefore designed to be most resilient of the road networks in Scotland. Local roads receive less funding per kilometre and are designed to be fit for purpose routes which in most cases mean they are less resilient than the trunk road network. The risk of significant events causing closure is therefore higher, but this is offset by the, generally, lower impacts.
There are various examples of the nature of impacts on local roads in recent years. A typical example Authority is Perth and Kinross Council (Perth and Kinross Council, 2011) which experiences at least one infrastructure failure on a major route each year. Other examples are:
- Major flooding events in 2002 caused significant disruption across part of the network. Repair costs at the time were estimated to be £230,000 of capital works, £400,000 of repair work and the longer term cost impacts (e.g. the potential shorter expected lifetimes of some drainage assets due to intensive wear and tear) are unknown. However, it was noted that even if the drainage system at the time had been built in accordance with up to date standards, the intensity of the event would still have caused failures and disruption.
- Severe weather caused landslips and partial collapse of a bridge on the Dunkeld to Rotwell Road at Toll Bridge in 2004. The route was closed to traffic, caused major disruption to local communities and the environment and the estimated cost of the preferred repair (which would enable full re-opening of the road) was estimated to be £403,000 at 2005 prices.
- In July 2010, a landslip on the B846 at Aberfeldy due to wet weather on an increasingly unstable embankment required repair at an estimated cost of £190,000. This example provides a good example of the way in which maintenance and operations can reduce such risks: part of the reason for the slip was assessed as possibly due to an overgrown tree on the embankment. Such risks are inherent across all similar networks and require the asset owner to prioritise budgets and assign expenditure to those areas at most risk. If funding is reduced, the number of 'at risk' sites therefore increases.
Local roads are also more vulnerable to failures of utilities under the road surface. The costs of these repairs fall to the utility companies but, nevertheless, cause major disruption to road users and, often, local residents. Although these are not a direct consequence of reduced maintenance funding, the reduction in maintenance work lessens the opportunity to coordinate utility works and road maintenance.
Whilst there is evidence of the costs of repair and economic impacts of closures and failures on road networks, it is not possible to adopt a traditional cost benefit analysis methodology to evaluate the whole of life economic cost of different funding scenarios.
The example of the failure at Rest and Be Thankful can be used as an indication of the range of impacts that might be expected in given situations. Assuming there is currently 1 route security impact of the same scale as rest and Be Thankful, in every year of the analysis period:
- It would need an increase in cost of approximately 7 times (per year) to generate the same quantified economic impact to road users as that expected from a 20% reduction in expenditure on carriageways;
- It would need an increase in cost of approximately 4 times (per year) to redress the savings in maintenance spend (works costs) from a 20% reduction in expenditure on carriageways.
Note that the above examples assume no safety risk of increased accidents (which would have a very significant impact if fatalities are involved) nor does it account for the qualitative impacts of community severance and accessibility discussed in Section 14.