Discussion

General

This Phase 4 study report is the final chapter in a series of previous reports, described in Section 1.2, and it is important to consider the prior phases in the interpretation of the Phase 4 results.

Each methodology provides different qualities and balances of evidence, but the triangulated results provide a compelling narrative around the difficulties and contrasts of visually and physically impaired users.

Considering the mix of qualitative and quantitative results and their statistical significance it is possible to have confidence in the findings of the Inclusive Kerbs Study.

Integration with Phase 1 - Comparison with Key Literature

Key previous research identified in Phase 1 was ‘Effective Kerb Heights for Blind and Partially Sighted People’ (Childs et al. 2009). This work, commissioned by the Accessibility Research Group for The Guide Dogs for the Blind Association was carried out by the Civil, Environmental, and Geomatic Engineering, University College London using the Pedestrian Accessibility Movement and Environment Laboratory (PAMELA) facility.

This work aimed to establish the effective kerb heights for blind and partially sighted people in the context of shared space developments, which were being used and developed during the time this study was being carried out, that reduced or eliminated kerb upstands to reduce the delineation of vehicles and pedestrians and remove indications of priority (see Manual for streets, Section 2.9, 2010).

Subsequent experience with shared space schemes has proved that low vision and moderate vision pedestrians tend to be brought into conflict with motor vehicles, and that kerb upstands and unlevel surfaces could be a hazard to low physical mobility users and those of low mental capability.

The Childs study used Bull-Nose and Half-Batter kerb profiles between 20mm and 120mm increasing in 10 mm increments up to 80mm, then jumping to 120mm.

All 36 participants were at varying levels of reduced visual capability, including both guide dog and long cane users. All had experiences of independent use of streets. There were no physical mobility or other capability varying participants.

Procedurally, participants experienced traverses of the PAMELA slabs with varying incidents of planar encounter (45° and 90°) with various kerb heights. Performance was recorded as categories of encounter. Detection was measured using a 10 point self-report verbal scale. Anxiety was also recorded as a 10 point self-report verbal scale; before, during and after.

Results were analysed from detection rates, anxiety levels, and approach angles.

• Participants showed higher confidence in detecting 80mm and 120mm kerbs (82% and 84% respectively).
• Detection confidence dropped for kerb heights of 60mm or less with 13 failing to detect 20mm kerbs.
• Participants were more confident when approaching kerbs from below rather than above.
• Stepping up the kerb resulted in higher detection confidence and lower anxiety compared to stepping down.
• Half-Batter kerbs were slightly easier to detect than Bull-Nose edge kerbs.
• Participants generally reported low anxiety levels throughout the experiment, dropping over time, irrespective of height.
• No significant difference in detection or anxiety scores, based on approach angle.
• Statistical differences were found in detection and anxiety scores between Half-Batter and Bull-Nose edge profiles. These were related to the order in which the conditions were presented (Day 1 vs Day 2).
• The study was unable to differentiate the detectability or effect of 50mm kerbs.
• The study also identified that after 40mm detection rates improved, with two non-detections for 40mm, one at 50mm, and zero at 60mm.

Childs et al. results were broadly consistent with the Phase 4 trials, but in comparison to this Inclusive Kerbs Research Study the methodology was severely restricted.

In particular, the self-report scales of anxiety and detection were psychologically simplistic and do not bear comparison with the comprehensive studies of this Phase 4 and the qualitative results of the Phase 3 results. The Childs study did not address the anthropological “lived experience” of navigating the streets, the participants were not asked about this and did not leave the controlled environment of the building (Davis, 2007).

Hence, despite prior work Childs et al. and others, there is still considerable uncertainty surrounding the use, upstands, and profiles of kerbs within road developments where individuals of varying functional capability are expected to navigate. Guidance, although detailed, often fails to cite recent academic research to evidence proscriptive guidance. 

The Childs study also did not address other capability variations such as physical movement, mental, or hearing issues, and was not based on the guidelines of Inclusive Design (Langdon and Thimbleby, 2010).

A wider range of kerb types were assessed and utilised throughout this Inclusive Kerbs Research Study, that also recorded the participants verbal comments during their encounters with different kerbs, including perpendicular, up kerb, and down kerb, and when asked to traverse the kerb width.

Unlike the ‘Effective Kerb Heights for Blind and Partially Sighted People’, the Inclusive Kerbs Research Study participants were presented with all conditions in a randomised order, reducing the impact of comparisons between different kerb experiences.

This Inclusive Kerb Study represents a multiple convergent methodology of research; combining civil engineering data; qualitative investigation of the lived experiences of kerb users; and laboratory experiments in controlled conditions, of disabled users’ reactions to kerbs.

Integration with Phase 2 – Comparison with Surveyed Kerb Heights

Phase 2 identified the engineering design considerations for kerbs, including delineation, gradient control, drainage control, and very low speed vehicle restraint. It identified that a delineator kerb between 12mm and 20mm in height is currently prescribed for segregated cycle tracks in the Traffic Signs Regulations and General Directions 2016 (Department for Transport, 2016) (TSRGD). It noted, however, that some subsequent design guidance indicates such a low profile may be disregarded by pedestrians and is difficult to maintain.

From the results of both Phase 3 and this Phase 4 assessment it can be shown that the delineator upstand heights in the TSRGD will have a high workload for the visually impaired. It can also be shown that the kerb upstand heights of 100mm or greater designed to act as minor restraints against slow moving vehicles significantly increase the workload for all users and to an impossible level for wheelchair users.

During Phase 2 the upstand and profile heights of kerbs around the City of Edinburgh were surveyed. The lowest kerb surveyed was 40mm in a new build commercial area. The highest kerb was 140mm in the city’s Old Town. Across all areas surveyed it was found that the average upstand was approximately 91mm, with a standard deviation of 23mm.

Applying the results of the Phase 4 research, the kerbs surveyed in Phase 2 would therefore likely pose at least Medium workload on all impaired users and High or Intermediate levels of workload on physically impaired users. All kerbs surveyed in Phase 2 should be detectable by visually impaired users.

In preparation for Phases 3 and 4 of the research, Phase 2 prepared and tested the interview methodologies used in Phase 3 and conducted quantitative analysis on data from the Family Resources Survey, 2019-2020 (National Statistics, 2021) to identify the percentages of the Scottish population with capability difficulties. This provided the theoretical ideal percentages needed for each of the capability difficulties for the research to match the wider Scottish population. This showed that 45% of those with functional difficulties identified as having mobility and dexterity issues, and 10% as having issues with vision.

Phase 2 also surveyed the footway and carriageway gradients, ambient noise level, and contrast of the kerb against the footway and carriageway. These areas of research were not continued in Phase 4 due to project constraints and the need to reduce variables to focus on the upstand height. However, these data sets could form part of further research into kerb detection and navigation.

Integration with Phase 3 - Comparison with Lived Experiences

Phase 3 focused on gathering real world lived experience qualitative data from interviews and site visits. Participants were asked in detail about their experience with current streetscaping, and kerbs in particular. They were then taken to three different sites within Edinburgh and asked to provide their commentary on navigating and traversing the kerbs and surrounding street. Their recorded commentaries provided insightful and detailed reports about the lived experience of individuals’ dealing with capability variations on Scottish streets.

These holistic results covered a wide range of interrelated physical contexts and considerations showing that the ability and decision to successfully interact with streetscaping and kerbs depends on a wide variety of factors.

Key Phase 3 findings included: 

1. Creating conspicuous edges is essential to addressing the challenge of navigation for visually impaired users.
2. Raised edges, such as kerbs, can form barriers to mobility, leading to risks, frustration, and longer journey distances.
3. Training for user groups with functional impairments is often not sufficient, widely available, or up to date with modern streetscaping styles.
4. The placement design of crossings is very important as these are the safest method for functionally impaired users to cross.
5. Route planning resources are required to assist users’ journeys, identifying inclusive design features.

When considering these with the Phase 4 results it can be evidenced there are distinctions and similarities of outcomes between visually impaired groups and physically impaired groups as they relate to the specific kerb height and type issues experienced by each user group.

Both visually impaired and physically impaired users evidenced a reluctance to interact with kerbs under normal circumstances. During the site visits the participants were presented with a kerb crossing location, they would assess the crossing situation and begin considering alternative strategies, rather than take the direct route across the kerbs. This often involved travelling along the road to find a more acceptable place to cross, such as a controlled crossing. If no such place was available their last resort was to ask for assistance.

From the site discussions and interviews it was reported by both groups that there were too few suitable crossings and that they were often not correctly configured to meet the needs of impaired users.

Within Phase 4 kerbs of 100mm were shown to be difficult and frustrating for all, and this extended to the baseline group. In Phase 3 this was also reported, with visually impaired participants reporting their concerns about the drop of kerbs (e.g. sprained ankles). This concern also reflects the finding that visually impaired users found it easier to detect kerbs from below than above. Physically impaired participants expressed frustration during their use of high kerbs in local residential settings.

The 50mm and 60mm kerbs were found to be challenging or aversive to wheelchair users during Phase 4, over the range of kerb profiles, with and without the assistance of a third wheel. The nature of this challenge was both psychological, related to anxiety, and also ultimately related to the potential physical injury form toppling, tipping or vibrating. However, from the interviews in Phase 3 we know that attaching the third wheel to the wheelchair is a timely task and needs to be completed at the start of the journey, meaning the user must know or anticipate using it on a kerb in advance. When attached it protrudes from the wheelchair some distance and it is reported to often cause problems when navigating through areas with pedestrians. Therefore, expecting wheelchair users to rely upon this third wheel (which some do not possess) would not form an inclusive design philosophy.

Interestingly low kerbs were not explicitly identified in Phase 3 as causing issues. However, areas where there is a lack of kerbs (or a delineation of minuscule upstand), such as raised tables and shared spaces, were identified as being an issue for visually impaired participants. In Phase 4 the 25mm kerbs were detected and traversed by both visually impaired and physically impaired groups. However, even these were difficult to detect and occasionally not noticed by some visual groups when approached from above.

Participants experience with cycleways was explored as part of Phase 3, and in Phase 4 a Cycle Segregation kerb, often used to delineate cycleways, was included in the testing. In Phase 3 wheelchair users were concerned about being trapped on a cycleway in the channel between kerbs. Both physically impaired and visually impaired participants reported significant concerns about the behaviour of cyclists in their vicinity. It was universally felt that there was a considerable risk of collision when attempting to cross a cycleway due to the behaviour of cyclists.

In Phase 2 the upstand of the kerbs at the cycleway were determined to be 55mm. In the Phase 4 laboratory trials the Cycle Segregation kerbs were found to be difficult to traverse by the wheelchair participants at 50mm, providing further evidence that these kerbs risk trapping wheelchair users on the cycleway. The 20mm and 25mm Cycle Segregation upstands could be easily traversed by the wheelchair participants but proved difficult to detect by the Visually impaired participants.

Both participant groups, Visually and Physically impaired, in Phase 3 agreed that their preferred method of crossing roads, cycleways, and other civil infrastructure was by seeking formal crossing points, first controlled (with traffic signals) and then uncontrolled crossings (without traffic signals). However, they agreed that these were often few and infrequent, often requiring significant detours in their journeys, especially in residential areas. This resulted in them resorting to cross at locations where the kerbs have an upstand, enduring the discomfort of the process and risking the inability to find or traverse the kerb on the other side.

It was established by mathematical interpolation (A.1 Linear Interpolation of Results) that kerb upstands within the range of 40mm-48mm could potential meet the needs of both the Visual and Physical capability groups by providing a kerb which is detectable and traversable with a moderate amount of workload. However, these upstands have not been tested during this research.

Discussion Summary

Despite previous studies like Childs et al., there remains significant uncertainty about the use and design of kerbs in road developments for people with varying abilities, especially as the Childs study did not consider other capability variations such as physical, mental, or hearing issues and was not based on Inclusive Design principles. This has not allowed existing guidance to provide robust academic support.

This Inclusive Kerb Study assessed a broader range of kerb types and included participants' verbal feedback on their experiences with different kerbs. This study used a mixed-method approach, combining civil engineering data, qualitative insights from kerb users, and controlled laboratory experiments with disabled users. Over the course of all four phases of the study a total of 33 contributions were made by participants to the study.

Phase 2 and 3 assessed the current condition of in-situ kerbs and gathered qualitative data from interviews and site visits, focusing on participants’ experiences with streetscaping and kerbs. Through their interview participants provided detailed commentary on navigating the kerbs and surrounding streets. Their insights highlighted the lived experiences of individuals with varying capabilities, covering a wide range of physical contexts and considerations.

This Phase 4 study concludes a series of previous reports, and understanding these earlier phases is crucial for interpreting its results. Each methodology offers unique evidence, but together they highlight the challenges faced by visually and physically impaired users. The combination of qualitative and quantitative data, along with their statistical significance, supports strong confidence in the findings of the Inclusive Kerb Study.

This phase also extrapolated an untested potential range of kerb heights which could potentially provide an equal workload for both the Visual and Physical capability groups. Phase 1 gave evidence that both 40mm and 50mm are currently allowed in some areas of guidance, and that many guidance documents do not specify any minimum upstands. British standard BS EN 1340:2003 ‘Concrete Kerb Units - Requirements and test methods’ sets out a standard range of kerb dimensions which can be specified on British roads, but not does not specify upstand heights. The safe installation of these requires a minimum of 1/3rd of the height of the kerb to be embedded into the ground, however, it is common for kerbs to be embedded deeper to provide a stronger foundation to increased durability and resilience. Commercially these standard kerbs are available with total height as low as 150mm. The upstand height is, therefore, dependent upon which guidance is applicable and the buried depth of the kerb. On schemes with suitable scale of purchasing bespoke kerbs can also be prepared which can be materially efficient.