Rumble strips are one of the most cost effective of the road safety engineer’s armoury, but actually proposing, funding and installing them can be a challenge. To guide you through this often long and meandering process from the point of view of the typical councillor or transport planner we have put together this long but in-depth guide to making rumble strips a reality.
Who decides? A brief introduction to the tiered structure of the UK highway system and the current policy and funding frameworks
The answer to the simple question of who has the power and authority to make decisions about the installation of rumble strips is far from simple. The UK has a confusing structure of highway authorities at both national and local level, with ownership and maintenance responsibilities parcelled up in different ways in England, Scotland, Wales and Northern Ireland. Further confusion is caused by the presence of devolved administrations with their own transport departments and enforcement powers.
So to start at the top, who decides whether rumble strips are installed on the Strategic Road Network of motorways and major A-roads operated by National Highways, previously Highways England?
National Highways
National Highways (NH) is a government owned company operating, maintaining and improving England’s motorways and major A roads. This Strategic Road Network (SRN) is the backbone of England’s highway infrastructure, totalling about 4,500 miles. These roads carry a third of all traffic and two thirds of heavy goods vehicle (HGV) traffic. As far as NH is concerned, they have complete autonomy to set design standards and installation priorities for rumble strips on their network and are answerable to the Secretary of State for Transport for how they exercise that discretion.
NH are required to implement, maintain and upgrade the SRN in line with its statutory five year Road Investment Strategies. These set funding levels and performance targets for the next five years. Rumble strip installations are likely to form part of larger safety improvement schemes. These schemes will typically either be in response to collision clusters identified through a systematic assessment process (see later) or bundled in with other scheme works like junction upgrades.
Risk assessment processes and a benefit cost ratio will drive NH decisions about which schemes offer the best value for money for road safety investment. To support these assessments NH has access to extensive traffic counts, a collision history going back several years for each section of road and engineering assessments by technical teams.
Local Highway Authorities
Outside the SRN, responsibility for the UK’s approximately 245,000 miles of local roads is divided between 152 local highway authorities in England, and separate networks of local authorities in Scotland, Wales and Northern Ireland. A local highway authority is typically a county council or a unitary authority, and has statutory responsibility for all non-trunk A, B, C and unclassified roads in its area.
Local highway authorities have a huge range of road safety challenges on their networks, but have less budget to invest in solutions than NH. A county council might be looking at rumble strips as an option for a rural A-road with a history of run-off collisions, an approach to a village where there are speeding concerns and a local neighbourhood street where residents are calling for traffic calming.
Each authority has its own prioritisation framework, but these must of course be compliant with their statutory responsibilities for road safety under the Traffic Management Act 2004 and the Road Traffic Act 1988.
The local authority’s road safety team would typically identify potential sites through analysis of collision data, or an elected member may bring a request from a local resident to consider rumble strips. A highway engineer will assess the technical suitability of any proposal, while other relevant departments, such as environmental health, will be consulted. There will also be an approval process, usually by a cabinet member or committee. In some authorities a major scheme requiring significant expenditure or which has attracted public objection will need to be approved by full council.
Parish and Town Councils
Before we move on, an important point to note is that parish and town councils, the organisations that are usually the closest to local communities, do not have highway authority status, and cannot make decisions about rumble strips or other traffic calming measures. They can advocate, campaign, and sometimes provide funding, but cannot force a principal highway authority to act.
The system is different in the devolved administrations. Transport Scotland runs the trunk road network in Scotland with local authorities managing the remainder. In Wales the Welsh Government has set up North and South Wales Trunk Road Agents to act as its highway maintenance agents, but the local authorities remain responsible for all other roads. In Northern Ireland, the Department for Infrastructure has responsibility for all public roads.
We have looked at the standard decision makers across the UK, but of course each administration has evolved their own design standards and approval processes, as well as taking different approaches to rumble strip installation. You should be aware that these systems are in place, but with guidance and expertise often shared UK wide, most of the materials we have included here will be relevant.
The Prioritisation Process
With tens of thousands of miles of road network and only a fraction of that amount of funding available for safety schemes, highway authorities have to have systems in place to decide where to invest limited resources. The old adage that if you listen to the “squeaky wheel” will see you at the right time and place might be true in a small number of cases, but in the main risk-based prioritisation is the way the majority of schemes are assessed and prioritised.
Collision Mapping and Cluster Analysis
The starting point of most prioritisation is a database of collisions. Highway authorities are required to keep detailed records of all reported injury collisions on their networks which are typically held in a database called STATS19. The data captured includes vehicle details, occupant demographics and injury severity as well as information about the collision circumstances, contributory factors and road conditions.
GIS allows highway authorities to map the locations of collisions in a way that can be interrogated for clustering sites and patterns, and allows characteristics such as single or dual carriageway, residential status, speed limit, or signage to be overlaid.
Collision clusters, a location where several collisions have occurred within a set distance over a set time period (the typical figure is five collisions within 1000 feet in five years), are an early indicator for the need for action. A bend in a rural road which has been the site of three serious collisions in three years is likely to get through the scorecards of most authorities as being a potential candidate for rumble strips, particularly if there is an obvious pattern in terms of common contributory factors such as vehicles running wide on the bend or not slowing enough for a side road. An authority will typically look at 3-5 years of collision data to make sure that they are not being swayed by a one off or statistical anomaly, although serious or fatal collisions in the past year might well be looked at immediately regardless of the longer term trends.
Risk modelling and Predictive Analysis
The smarter authorities have moved towards some form of predictive risk modelling. This approach uses the characteristics of a road to assess where there might be a collision risk even where this has not yet materialised in collision history. This is ethically and economically sounder than a purely reactive approach that waits for collisions to occur before acting.
Roads can be assessed against factors such as geometry, traffic volumes, speed limit and roadside hazards. The average collision frequency per million vehicle kilometres on similar roads with similar risks can also be a useful input. There are different methodologies for doing this that use more or less data and/or judgement to come up with a risk assessment of a road section. The UK Road Assessment Programme (RAP) methodology for example, gives a road section a star rating based on its inherent safety characteristics. A single carriageway rural road with tight bends, no centre line rumble strips and unforgiving roadside trees and hedges might be low star, which might then flag it for consideration.
Crucially for the assessment of the appropriateness of rumble strips, this risk assessment data can be combined with traffic volume data to target the locations that will prevent the most casualties.
Multi-Criteria Assessment Frameworks
The typical authority will also use some form of multi-criteria assessment framework to score schemes on a range of factors, with the scheme that scores highest being at the top of the priority list. A framework might score potential schemes against a range of factors, for example;
- Collision history (weighted by severity, fatalities score highest)
- Collision density (collisions per million vkl)
- Potential casualty savings (predictive modelled)
- Cost effectiveness (benefit:cost ratio)
- Strategic fit, i.e. part of routes to school initiative, rural road safety campaigns etc.
- Community concern (petition, councillor representations)
- Feasibility/deliverability
- Complementarity with other works
A scheme would accumulate points across these factors to create a prioritisation score. The process is not entirely mechanistic, and professional judgement is still required, particularly where there have been recent serious or fatal collisions that have had a high impact on communities, or where specific road characteristics that create a high obvious risk that rumble strips could address.
Road Safety Audits
Road Safety Audits (RSAs) for new road schemes and major alterations are a statutory requirement on the SRN and in many local highway authorities. Occasionally the reports of these independent assessments, which are undertaken by suitably qualified engineers or teams, identify existing roads where rumble strips could address specific safety deficiencies. If a recent audit has been done then this could be a quick way of getting a scheme up the priority list.
An audit might pick up for example that a recently resurfaced road has had skid resistance improved but no edge line rumble strips added to warn drivers of the verge as they begin to drift over to the off side, an addition that would be relatively inexpensive and could prevent run-off collisions.
Urban and Rural
A particular issue with most prioritisation processes is that there is a bias against rural roads. These typically have a lower collision frequency than urban areas with their higher traffic counts and density of junctions, but are responsible for a disproportionate number of serious and fatal casualties. Rumble strips are a very effective solution in rural areas. Alerting drivers who have been fatigued on monotonous A roads, providing warning of bends and restricting side road junctions, or preventing run off collisions on roads with limited room for recovery before a collision. Authorities must be careful in their prioritisation frameworks to not systematically disadvantage rural communities.
Funding streams: following the money
A rumble strip scheme that has survived the various prioritisation exercises remains only a theoretical concept until it has been funded. This section outlines the various funding streams that are available to fund installation, to help officials think about how schemes can be taken from prioritised lists into delivered schemes.
Local transport plans and core funding
For the majority of local road safety schemes, the principal source of funding will be the authority’s own capital and revenue budgets, with priorities identified and directed as part of Local Transport Plans (LTPs). LTPs were five-year statutory local transport strategies that set out authorities’ priorities for transport investment. Highway authorities receive funding from central government, via a variety of settlements, to pay for their statutory activities. However, the funding available via these settlements has been under significant pressure over the past ten years. For most highway authorities, this budget is then allocated between numerous competing demands – filling in potholes, maintaining bridges, major junction remodelling, subsidising public transport, supporting walking and cycling and paying for road safety schemes. Rumble strips are relatively inexpensive, particularly compared to major junction remodelling or even speed tables, and represent good value for money, but they are still in competition for funding with other priorities within the local transport plan. A centreline rumble strip scheme, typical costs might be £5,000-£15,000 per kilometre of road, depending on specification. Edge line rumble strips are slightly less expensive to install. The costs are relatively modest when it comes to infrastructure projects, but start to add up when multiple sites are involved.
Specific road safety grants
On occasions, the central government will announce specific road safety funding programmes to which local authorities can bid. The Safer Roads Fund, which was launched in 2017 and had £100 million over three years, specifically targeted the 50 highest risk local A-road sections across England. A number of these successful bids included rumble strip installation. Similar programmes from time to time present an opportunity to deliver schemes that might otherwise remain unfunded on prioritisation lists. They do require a significant effort from the authority to develop a bid, and there is always a risk that it won’t be successful.
The Department for Transport (DfT) also sometimes announces road safety funding streams around particular themes: rural road safety, motorcycle casualties, vulnerable road users, etc. where rumble strips might form a deliverable intervention.
Monitoring announcements from central government and being ready to develop “shovel-ready” schemes that can be quickly turned into a funding bid is a useful skill for a proactive road safety team.
Section 106 and community infrastructure levy
A second source of development-related funding can be triggered. Section 106 is a planning obligation that a local planning authority and a developer can agree, to ensure that the impact of development is appropriately mitigated. This might require a contribution from the developer towards transport infrastructure improvements that the development necessitates. Where a new development will generate traffic on a road that has already been identified as needing safety improvements, a contribution from the Section 106 funding envelope might be available to pay for rumble strip installation. The Community Infrastructure Levy (CIL) is a similar concept, where development is charged for and a local levy to pay for infrastructure built up, rather than reliant on individual Section 106 agreements. CIL can in principle support road safety schemes, but requires the authority to have identified this in their infrastructure delivery plan.
Parish and community funding
Parish councils and community groups are increasingly able to make contributions towards road safety schemes which they have championed. Highway authorities have a statutory duty for road safety, and cannot be required by parish councils or community groups to take action at a location or deliver a particular type of scheme. But if a parish council, or other group, make a financial contribution towards a scheme, the highway authority can accept this money and deliver the scheme sooner than it might otherwise have been possible. A typical arrangement might be a parish council contributing £10,000 to a scheme that would cost £25,000, with the highway authority making up the balance and taking responsibility for delivery. Agreements need to be explicit about the standards of design and expected maintenance; it is useful to have some thoughts in advance about what might be done if the scheme proves controversial after installation.
Maintenance budgets and opportunistic installation
A funding route that is often under-utilised involves making rumble strip installation part of programmed maintenance. If a road is programmed for resurfacing, the additional cost of installing rumble strips is relatively low, and the same machinery and workforce will be carrying out both activities, in any case. A small investment in forward planning – keeping a list of where rumble strips would be beneficial, and cross-matching this against programmed maintenance programmes – can help identify opportunities to install them cost-effectively at the same time as other maintenance activity. This does require road safety and maintenance teams to communicate with each other: two parts of the highway department that are not always noted for the quality of their communication.
Insurance and compensation payments
Ironically, another funding source for rumble strips is the cost of not having them. An authority that receives repeated compensation claims for collisions at a location will find that the cost of settling claims and making good can sometimes exceed the cost of remedial measures. This should not be the driving force behind a decision – the primary objective is, and should remain, preventing casualties. But it does provide a financial argument to take to budget-holders when trying to secure funding for a scheme that is otherwise sitting unfunded on a priority list.
Community engagement and objections
Aspects of technical detail and funding routes are important when considering rumble strip installation, but perhaps the most challenging barrier to implementation is often the human one. Community engagement can make or break a scheme, and local objection is the most frequent hurdle.
The noise issue
Rumble strips work by creating vibration and noise when a vehicle passes over them. In that sense, it is a “feature” rather than a “bug”. The noise and vibration is the safety mechanism at work: alerting an inattentive driver that they have wandered out of their lane, or that they need to slow down. The characteristic rattling sound created as vehicles pass over the rumble strips is the price that residents living adjacent to treated roads will pay for the increased safety for road users. However, this very same feature also generates the most frequent source of objection.
Centreline rumble strips will affect fewer properties, as they are furthest away from the roadside, and milled strips are quieter than raised profile strips. Rectangular (bar) profiles are louder than sinusoidal (curved) profiles. Rumble strip design and specification can be adapted to make them quieter. Highway authorities need to think about which is the most appropriate and acceptable to use near residential properties: there is often a trade-off between effectiveness and noise, particularly for centreline rumble strips. This is an issue that needs to be considered at the design stage: potentially mandating a quieter design near homes, even if it is slightly less effective or more expensive.
Pre-installation consultation
Community engagement should begin before the decision to install is made, by informing the community about the proposed scheme, and giving them a chance to find out more. If the community is informed and engaged from the start, objections are less likely when the work goes out to tender. Consultation can take a variety of forms:
- Letters to properties within a set distance from the proposed installation (perhaps 50m or 100m, depending on local policy)
- Public exhibitions or drop in sessions where members of the public can view the plans, and speak to the engineers directly
- Online consultation portals with plans and visualisations
- Engagement with parish councils and residents associations
- Engagement with local councillors who can act as champions to their constituents
Consultation needs to be open and honest about the implications of the proposed scheme, including its noise implications. The traffic calming register of objections written in is often characterised by residential groups over-emphasising noise impacts. Authorities need to counter this by being just as clear about the safety benefits. The consultation process should, where possible, include access to collision data to show where and why the chosen location has been identified as having a safety problem. Explaining the types of collisions the rumble strips will prevent and quantifying the expected casualty reduction helps to explain to a community why their road has been prioritised for treatment. Site visits to existing rumble strip installations can be useful, as often the actual noise generated is lower than people anticipate, particularly if they have had their imagination inflated by exaggerated accounts.
Responding to objections
Objections, particularly on the grounds of noise, will still happen, even where communities have been fully consulted and engaged. Some residents will prioritise their perceived personal acoustic environment over the safety of road users, particularly if they have not personally experienced or witnessed a serious collision. The highway authority must balance this against their statutory duty of care to ensure safety on the roads. A number of responses may be possible, including:
- A quieter design with different strip characteristics
- A shorter length of installation to exclude sections immediately adjacent to properties, while retaining the highest risk sections
- An explanation that speed bumps, speed humps and speed tables would have generated more noise and vehicle emissions
- Acoustic monitoring data from other, similar installations, demonstrating that the increase in noise is only marginal, and within acceptable limits
- There is an alternative, which is to continue with collisions at a location. The noise, calls to the emergency services, disruption to residents, and trauma, all of which impose a community impact, but of a different sort.
In some cases, highway authorities may have no option other than to proceed, particularly where the safety case is robust, but the key is to maintain dialogue and make it clear that the objections have been fully considered.
Post-installation monitoring
Community engagement does not have to stop with installation. Monitoring collision rates and demonstrating the impact of the scheme to communities demonstrates an authority’s accountability and the scheme’s success. If rumble strips demonstrably reduce collisions and casualties, publicising this is good publicity for future schemes. Equally, if something has gone wrong – the noise levels are greater than expected, or the strips are ineffective at a site because of something specific to that location – then authorities should acknowledge that, and think about whether something can be done to mitigate this.
Setting a period after which a scheme will be assessed and reviewed (6 or 12 months after installation) and any changes made, if necessary, can be a useful way to reassure concerned residents that the authority is still engaged and responsive. Better still, they will have data to hand when that period is reached to help inform the decision.
Surface Wear and Re-Marking
Road markings including the edge line, centre line and hatching that accompany rumble strips will become more faded over time from the action of traffic wearing them away and exposure to the elements. As the markings fade this can reduce the visual prompts they offer alongside the physical warning that is the rumble strip itself. Highway authorities should include the locations of their rumble strips within their line marking renewal programmes, refreshing them as needed on a suitable cycle, usually every two to four years dependent on traffic volumes and materials used for the marking.
The rumble strips themselves can also become worn over time with some raised profile designs more susceptible to snowplough damage and thermoplastic types less resilient to heavy trafficking. The condition of strips should be monitored and any repairs or replacement actions carried out before they become ineffective. Some authorities have an annual safety scheme inspection process that includes their rumble strips to check for any maintenance actions required before the effectiveness of the scheme is reduced.
Winter Maintenance Considerations
Rumble strips present some additional considerations for winter maintenance operations, with raised profile strips catching the blades of snowploughs and possibly causing damage to both the rumble strip and plough. There can be an accumulation of ice and snow in the cut grooves of milled strips which can require additional attention during gritting activities. Such considerations should influence design decisions around the use of milled rather than raised strips where winter maintenance access is particularly important, for example, and winter maintenance operators should be made aware of the locations of any rumble strips when planned winter operations are being scheduled so they can take those into consideration during their work.
Budgeting for Lifecycle Costs
The cost of delivering a rumble strip scheme is not just the installation but many decades of maintenance. Highway authorities should be calculating whole-life costs when appraising such schemes and ensuring their maintenance budgets can accommodate the additional costs associated with the maintenance of rumble strips. A scheme that may appear good value when judged on installation costs alone may be less attractive when true lifecycle costs are taken into account. Rumble strips are a relatively low-maintenance intervention when compared to the moving parts of mechanical traffic calming devices or new junction layouts that may require much more frequent maintenance actions to keep them functioning and attractive. On this basis they are likely to be good value for money even when whole-life costing is taken into consideration.
Maintenance Responsibilities and Accountability
Maintenance responsibilities should be clear with a written arrangement agreed particularly in cases where multiple stakeholders are involved in a scheme. Where a parish council has contributed towards funding, for example, is there any maintenance expectation or responsibility or is it all on the highway authority? If maintenance actions are more costly than anticipated who pays for the overspend? Such issues should be agreed in writing before a scheme is installed to avoid arguments and misunderstanding later on.
Conclusion
The delivery of rumble strip schemes on the UK’s road network is not simply a matter of technical design and installation, but navigating a complex environment of institutional, political, financial, community and social factors. Highway authorities, parish councils and other stakeholders must not only be skilled in the engineering and safety aspects of such interventions, but in the political, financial and social skills needed to advocate for their schemes, secure funding, and maintain the trust and confidence of local communities.
Ownership of roads in England, Wales and Scotland is fragmented between National Highways for the strategic network and 152 local highway authorities for all other roads. National Highways’ remit for the strategic road network has led to the development of a consistent design standard for rumble strips, but local authorities have a more varied approach. A total of 152 councils means 152 different budgets, priorities, relationships with parish councils and communities and delivery cultures, creating a patchwork of standards and practices across local roads. While this complicates efforts to drive a consistent national approach to rumble strip schemes, it also allows space for innovation and improvement, with more progressive authorities developing good practice that can be learned from by others.
Prioritisation of schemes is always a challenge for highway authorities given a limited resource base and a seemingly infinite number of possible interventions. Balancing the needs of the strategic road network, local roads, the capital maintenance backlog and planned new developments in the allocation of funding and engineering resources is no easy task. Clear, evidence-based frameworks for scheme prioritisation and delivery are vital in ensuring limited resources are spent where they will have the most impact on safety and meeting community needs, but these must also be flexible enough to allow for local priorities and professional judgement.
The availability of funding for local authorities is a major driver in the expansion of rumble strip use. When budgets are tight, the costs of installing rumble strips, even where their lifetime maintenance requirements are low, can be prohibitive. Creative authorities will explore multiple funding sources, alignment with planned maintenance and community partnership working to maximise delivery. Local communities’ concerns over noise are a reality when it comes to rumble strips and require careful handling with honest communication, a willingness to discuss trade-offs and where necessary adaptation of design to suit local circumstances without compromising the safety effectiveness of the scheme.
Maintenance, too, is critical to the success of a rumble strip scheme. It is easy to lose focus on this aspect during the planning and delivery phase of a new scheme, but it is during maintenance that the safety benefits of rumble strips are delivered or lost. Planning for their maintenance during the initial scheme design, budgeting for their whole-life cost and establishing clear responsibility for maintenance in writing helps ensure that the safety investments being made today continue to protect road users for decades to come.
Rumble strips are a proven, cost-effective way to reduce casualties for local government officials, councillors and transport planners committed to making their road networks safer. Understanding the realities of delivery including the key stages from initial prioritisation through to scheme delivery and the importance of maintenance and communication will help decision-makers navigate the challenges and deliver the safety benefits rumble strips can provide. In an era of limited resources and competing priorities making informed, evidence-based decisions about road safety interventions has never been more important.
