This thesis derives and validates Performance Indicators for Safe Mobility for Older Road Users in Urban Areas. Performance Indicators are objective, auditable parameters, which when used as a set can provide additional information to decision-makers about the operation of the transport system. Great Britain, in common with many countries across Europe has an ageing population. The proportion of older people who hold a driving licence and have the use of a car is also expected to rise, with future generations of older people travelling further and more frequently than previous generations. Older road users are already over-represented in traffic fatalities, particularly in urban areas. Measures to protect older road users from risk in traffic will be of crucial importance as the population ages. However, against this background the need remains for them to access key facilities such as shops, leisure activities and health care. Maintaining independent mobility is essential in maintaining mental and physical health. Traditionally, outcomes-based measures such as accident or casualty figures have been used to monitor road safety. Techniques such as hotspot analysis have identified locations on the road network where accident numbers are high, allowing modifications to road infrastructure to be designed and implemented. Using outcomes measures alone however, it is difficult to ascribe improvements in accident or casualty figures to particular policy interventions. Moreover, the effect of road safety interventions on other related policy areas mobility being one is impossible to assess without access to detailed, disaggregated exposure data. To make fully informed policy decisions about infrastructure design and how it affects older users, a better understanding of the linkages between safety and mobility is required. Performance Indicators offer the possibility to look at these linked policy objectives within a single framework. Focus group data was used in conjunction with the results of previous studies to identify the infrastructure features which present a barrier to older users safe mobility in urban areas. These included factors which increased risk, such as wide carriageways, complex junctions and fast-moving traffic, and factors which hindered mobility, such as uneven or poorly maintained pavements, poor lighting and traffic intrusion. A thematic audit of infrastructure in a case study city (Coventry) was undertaken, in order that the incidence of such infrastructure could be recorded. It was found that in many areas of the city, safe mobility for older road users was not well provided for, with the majority of locations having barriers to safety and/or mobility for both drivers and pedestrians. The audit data was then used to calculate a set of Performance Indicators, presented via spider graphs, which describe the degree to which the infrastructure caters for the safety and mobility of older drivers and pedestrians. The spider graphs allow for easy comparisons between the different geographical areas, and also between the different policy areas, allowing policy priorities to be identified. The calculated Performance Indicators were validated using case studies collected from the focus group participants. The case studies identified features that affected travel habits by causing a change of route or change of mode, providing evidence of the link between infrastructure design and safe mobility for older users. The results of the Performance Indicator analysis were then compared to accident figures, in order to identify differences between the two approaches, and to understand what policy implications would result from a monitoring framework that used Performance Indicators for safe mobility, rather than outcomes-based measures alone. One implication of the Performance Indicator approach is that it may identify different areas for priority action from those identified by accident or casualty figures. A location which does not have high accident numbers may nevertheless perform poorly on a Safety Performance Indicator measure. This is because older users who feel at risk make different route or mode choices to avoid the infrastructure, the lower accident rate being explained by lower exposure to risk. Conversely, measures to promote independent mobility for older users may increase their accident involvement, not because the environment becomes more risky, but because the exposure of older users to risk increases, because they are willing and able to walk or drive in an area they previously avoided. The thesis concludes that infrastructure design does not currently cater well for the needs of older pedestrians and drivers, and that a framework which incorporated Performance Indicators could make more explicit the trade-offs between safety and mobility, and between different categories of user. This additional information would enable policy makers and practitioners to make more informed decisions about how to prioritise competing objectives in complex urban areas.

The hazard perception skill of a driver refers to their ability to identify potentially dangerous events on the road, and is one of the only driving-specific skills that has been consistently linked to accident rates. Hazard perception tests are used in several developed countries as part of the driver licensing curriculum, however little research has been done in developing countries where road safety is a primary concern. The extent to which hazard perception skill transfers to different driving environments is also unclear. This thesis therefore has two major aims: to examine hazard perception in a cross-cultural context, and to validate a hazard perception test for potential use in driver licensing in lower-income, developing countries. Most of the experiments in this thesis compare hazard perception skill in drivers from the UK – where hazard perception testing is well established – and drivers from Malaysia – a developing country with a high accident rate where hazards frequently occur. Typically, hazard perception skill is assessed by showing participants clips filmed on the road and asking them to respond as soon as they detect a developing hazard, with shorter response times reflecting greater levels of skill. Chapter 2 presents evidence that Malaysian drivers may be desensitized to hazardous road situations and thus have increased response times to hazards, creating validity issues with the typical paradigm. Subsequent chapters therefore use a predictive paradigm called the “What Happens Next?” test that requires drivers to predict hazards, leaving performance unaffected by hazard desensitization. Malaysian drivers predicted hazards less accurately than UK drivers in all cross-cultural experiments, indicating that exposure to a greater number of hazards on Malaysian roads did not have a positive effect on participants’ predictive hazard perception skill. Further experiments indicated that explicit knowledge plays a minor role in the “What Happens Next?” test, and that experienced drivers appear to compensate for reduced visual information more effectively than novices. Experienced drivers from both Malaysia and the UK also outscored novices in all experiments using the predictive paradigm, suggesting the “What Happens Next?” test provides a valid measure of hazard perception skill and may offer a practical alternative for hazard perception testing in developing and even developed countries.

Children and older adults are overrepresented in pedestrian accidents (Department for Transport, 2010a, 2010b). Gaze behaviour is cited as a contributing factor in the majority of such accidents (Department for Transport, 2010a, 2010b); however, remarkably little is known about how children, adults and older adults control their gaze during either real or simulated road-crossing tasks. Because evidence suggests that behaviour in the laboratory may not accurately reflect that in more realistic situations (Dicks et al., 2010; ‘t Hart et al., 2009), this thesis used a real-world, active road-crossing task to compare, for the first time, how pedestrians across the lifespan direct their gaze during real road crossing. A total of 70 participants took part in the studies: 42 children (mean age 8.6 yrs, SD = 0.4); 14 young adults (mean age 24.1 yrs, SD = 4.5) and 14 older adults (mean age 70.7 yrs, SD = 4.1). In the first experiment, participants were escorted on a short walk while wearing a mobile eye tracker and asked to cross the roads along the way when they felt it was safe to do so. Gaze behaviour during the last 3 seconds before crossing the road at a signalised crossing was analysed. Both children and older adults directed their gaze significantly less often to traffic-relevant features (such as the road and vehicles) than young adults. However, their gaze patterns were very different. Older adults looked more at the ground ahead of them, which most likely reflects a functional adaptation to reduce the risk of tripping and falling as falls represent a serious risk in this population (Jensen, 1999). Children fixated traffic-irrelevant features more, which may indicate poorer attentional control or insufficient practice or experience. A serendipitous finding from this study was that the presence of a distractor (ice cream) acted to further draw attention away from the direction of oncoming vehicles in the sample of children. Based on these findings, a subsequent aim of the thesis was to explore whether two road-crossing training interventions (Crossroads and Safety Watch) would improve the amount of time children fixated traffic-relevant features of the environment: neither programme was found to have a significant impact on gaze behaviour compared to the control condition (no intervention). Another aim of the thesis that followed from the results of the first experiment was to further examine the attentional control of gaze behaviour in children. Two simulated road-crossings were purposely developed in the laboratory, allowing more controlled investigation of gaze behaviour at (simulated) signalised and unsignalised crossings, with and without a non-spatial secondary task (counting in threes). It was found that the addition of this secondary task affected children's gaze behaviour in one of the simulation types but not the other. This demonstrated that cognitive processes are context dependent and not invariant across conditions. In light of the growing concern raised with respect to the use of artificial laboratory settings and tasks, the final aim of this thesis was to compare gaze behaviour of children under three display conditions: monitor simulation, projector simulation, and real-world; the results suggested that behaviour in the laboratory did not correspond with real-world behaviour. In real road-crossing situations, children looked significantly more often at the ground ahead of them (walkway) and at lights and signs than when performing in the “monitor” or “projector” simulations. These findings further emphasise the context-dependence of cognition and behaviour. This thesis contributes to the argument that a real-world setting provides rich and meaningful data and that, although the laboratory setting has certain methodological advantages, transfer of laboratory findings to the real-world context cannot be assumed. Similarly, road-crossing skills trained in a simulated setting (on a computer) do not appear to transfer to the real-world context. This thesis therefore advocates a real-world approach to the research and training of behaviour and underlying cognitive processes.

Road safety has become a major concern due to the increased rate of deaths caused by road accidents. For this purpose, intelligent transportation systems are being developed to reduce the number of fatalities on the road. A plethora of work has been undertaken on the detection of different styles of behaviour such as fatigue and drunken behaviour of the drivers; however, owing to complexity of human behaviour, a lot has yet to be explored in this field to assess different styles of the abnormal behaviour to make roads safer for travelling. This research focuses on detection of a very complex driver’s behaviours: ‘tafheet’, reckless and aggressive by proposing and building a driver’s behaviour detection model in the context-aware system in the VANET environment. Tafheet behaviour is very complex behaviour shown by young drivers in the Middle East, Japan and the USA. It is characterised by driving at dangerously high speeds (beyond those commonly known in aggressive behaviour) coupled with the drifting and angular movements of the wheels of the vehicle, which is similarly aggressive and reckless driving behaviour. Thus, the dynamic Bayesian Network (DBN) framework was applied to perform reasoning relating to the uncertainty associated with driver’s behaviour and to deduce the possible combinations of the driver’s behaviour based on the information gathered by the system about the foregoing factors. Based on the concept of context-awareness, a novel Tafheet driver’s behaviour detection architecture had been built in this thesis, which had been separated into three phases: sensing phase, processing and thinking phase and the acting phase. The proposed system elaborated the interactions of various components of the architecture with each other in order to detect the required outcomes from it. The implementation of this proposed system was executed using GeNIe 2.0 software, resulting in the construction of DBN model. The DBN model was evaluated by using experimental set of data in order to substantiate its functionality and accuracy in terms of detection of tafheet, reckless and aggressive behaviours in the real time manner. It was shown that the proposed system was able to detect the selected abnormal behaviours of the driver based on the contextual data collected. The novelty of this system was that it could detect the reckless, aggressive and tafheet behaviour in sequential manner, based on the intensity of the driver’s behaviour itself. In contrast to previous detection model, this research work suggested the On Board Unit architecture for the arrangement of sensors and data processing and decision making of the proposed system, which can be used to pre-infer the complex behaviour like tafheet. Thus it has the potential to prevent the road accidents from happening due to tafheet behaviour.

Background: Drug use among the driving population is a major hazard to road safety and has been the subject of widespread research worldwide. In an attempt to detect and appropriately prosecute “drug-drivers”, the UK has made legislative changes and has introduced Field Impairment Tests (FIT) in the Railway and Transport Safety Act 2003. These FIT, which are identical to the Standardised Field Sobriety Tests (SFST), were devised in the USA in the 1970s to identify clinical signs of impairment due to alcohol intoxication, but were not designed or intended to identify drug-related driving impairment. Concerns have been expressed that FIT are too difficult for their stated function, and are also inappropriate tests, since although they have been validated for alcohol effects they have never been validated for the effects of drugs. This thesis has sought to clarify matters and has questioned the validity of FIT by testing two opposing hypotheses – 1) FIT are reliable and valid tests of drug-related impairment to drive - and drug-free individuals perform well on all tests. 2) FIT are not reliable and valid tests of drug-related impairment to drive - and are too difficult for some groups of drug-free individuals to perform. Methods: A questionnaire was designed and a postal survey was undertaken of 960 Forensic Medical Examiners (FMEs) who were asked to give their opinion on the Field Impairment Tests (FIT). The responses of the FMEs were analysed in detail (chapter 3). FIT were then carried out on three separate groups of 100 subjects in police custody who were all known to have used no drugs for a period of at least 8 hours prior to the testing process (chapter 4). Group A subjects were opiate dependent; Group B were subjects who received legally prescribed methadone; Group C individuals denied any form of drug use. All study groups were simultaneously examined using conventional psychomotor tests, and the results were compared using detailed statistical analysis with logistic regression and summative scores. Results: Returned FME questionnaires showed 63% of FMEs considered the tests “about right” but a significant number (p<0.0001) of 33% of FMEs stated FIT were “too difficult”. The studies on subjects in custody clearly showed 82% of group A; 44% of group B; and 19% of group C were unable to complete FIT satisfactorily, although only 12% of group A; 2% of group B; and 3% of group C were unable to successfully perform conventional psychomotor and cognitive tests. These findings clearly supported the assertions held by 33% of FMEs surveyed that FIT were too difficult for their stated purpose and that poor performance in FIT could not be regarded as definitive evidence of drug-related impairment in driving ability. VII Conclusions: The results of the research studies conducted have provided very strong support in favour of hypothesis 2) FIT are not reliable and valid tests of drug-related impairment to drive - and are too difficult for some groups of drug-free individuals to perform. In an attempt to overcome the problems in respect of FIT, specific proposals have been offered including the introduction of a new battery of more relevant clinical tests of impairment (CTI); a change in the method and manner in which the proposed new tests are applied; and possible legislative and administrative measures which might be introduced to more appropriately and effectively tackle this on-going hazard to road safety.

The overall aim of this thesis is to corroborate whether the Situation Awareness (SA) of older drivers is deficient to that of younger driving groups, due to the onset of age-related cognitive decrements. This is important to ascertain due to a presumed linkage between the concept and accident causation. In addition, the research undertaken to date to investigate this linkage has exclusively utilised rather artificial driving simulators and simulations. Thus there is a need for data from more ecologically valid methods. The research studies reported here have sought to preference on-road assessments (of different complexity), and to capture what information was selectively perceived, comprehended and reacted to; rather than, as in previous work, what was recalled. To achieve this, a Think aloud methodology was chosen to produce narratives of a driver s thoughts. This method was advantageously unobtrusiveness, but also flexible - it could additionally be used to compare an individual's SA to a driving performance measure, Hazard Perception. The driving-based studies undertaken found that for a relatively non-taxing route, an older driver group could produce cohesive awareness in parity with a younger driver group. However, the concepts from which that awareness was based upon drew more on general, direction based, concepts, in contrast to the younger group s focus on more specific, action based, concepts, and rearward and safety-related cues. For a more cognitively taxing route, the younger group produced significantly higher (p < 0.024) individual SA-related scores than their older counterparts. But the concepts/cues both groups relied upon remained similar - particularly in regards to the ratio of those indicative of a rearward and/or a safety-related focus. In a video-based study, however, and in contrast, the older driver group s SA scores improved sufficient to outperform a younger group, but, despite this, not for video-based scores indicative of Hazard Perception (HP). In this latter regard, age-related decrements appeared to be more influential, as the older group felt they were under time pressure during a HP test. However, the difficulty this presented appeared to advantageously bring more attention and effort to the task, which were argued as important factors for the uplift in their SA scoring. The thesis also showed that older groups judgement of the actual complexity of a driving task could potentially be deficient to that of younger driver groups. This could cause problems as incorrect perceptions could deflate the relevance and cohesiveness of information being processing. In contrast, the perceived complexity of a task could bring a rise or fall in SA score for both groups. Such results raised questions as to the impact of cognitive decrements, relative to task difficulty and related effort whilst driving. It also provided evidence that Situation Awareness, rather than being uniformly good or bad, could, like any other psychological construct, be prone to change. These aspects were drawn together in a proposed model of driving SA.

Most drivers are aware of the distracting effects and possible dangers of using their mobile phones while driving. Many studies have investigated this effect and although not all have found large changes in driver performance, all have concluded that nothing good can come from this behaviour. Without adding to the wealth of studies in this area, this PhD aimed to discover what kinds of attitudes drivers have towards these technologies, how these drivers behave in a ‘natural’ situation and how these drivers can be persuaded to cease using these technologies while driving. The first study was a large questionnaire aimed at measuring theory of planned behaviour constructs from drivers towards five in-car technologies; hand-held mobile phone use, hands-free mobile phone use, text messaging, MP3 player use and satellite navigation use. These identified that attitudes in particular are important predictors of intentions and behaviour. Regression models explained 38-76% of the variance in past behaviour for the five technologies showing that the theory of planned behaviour is a useful tool in understanding these kinds of behaviour. Studies 2 and 2.5 aimed to discover whether in-car technology could have a positive effect on driver performance with the use of a ‘risk monitor’. These results indicated that heart rate could be influenced in a simulator by instilling a sense of risk. Although no differences in driving variables were found, participants’ heart rates increased as accident risk increased, importantly showing that feelings of risk arousal can be induced in a simulated environment. Studies 3 and 4 used a novel design in which participants were given the choice to interact with an MP3 player and skip music that they personally did not like. Study 3 found that participants spent a significant amount of time looking away from the road when interacting with the device. However, no differences in lane deviations or speed deviation were found. Study 4 was then conducted to increase sample size and increase variability by introducing a second speed limit. Results showed that participants had a tendency to miss this speed limit due to interactions with the device. Main effects were found for standard deviation of speed, with the easy skip condition showing more variability than the control condition, possibly reflecting compensatory behaviours due to technology use. Eye data also showed the effects of technology use where glance durations were significantly longer while skipping compared to controls and were significantly longer during hard compared to easy tasks. Study 5 aimed to combine the risk monitor studies with the MP3 studies and create an environment where participants were free to interact with the device if they wished, but were also given some information on their risk of accident to take into account. Drivers on low risk roads interacted with the device more often than on high risk roads and spent more time listening to unpleasant music when the risk tone was present. In terms of driving measures, participants reached higher speeds when the tone was not present, while mean speeds showed a tendency to be lower when the tone was present. Study 6 was an intervention study which, informed by the results of study 1, created an intervention based on changing drivers attitudes towards technology use while driving. After the intervention was given, drivers completed a similar study to the MP3 experiments. This meant that not only could attitudes be measured at different time points, but actual behaviour relating to technology use could be measured. Theory of planned behaviour interventions are often criticised as they tend to measure behaviour by questionnaire rather than tangible measures of behaviour and so this was an advantage to this study. However, the intervention showed no significant effect on attitudes or MP3 music skipping behaviour. However, a significant correlation was found between the number of times a participant skipped and measures of driving violations. The challenge for future work will be to determine how attitudes can be changed towards technology use and whether further experiments may observe ‘natural’ behaviour in relation to different types of technology.

Each year millions of people around the world are killed or injured due to being involved in collisions while driving on the roads, with young and inexperienced drivers most likely to be killed or injured. Numerous studies have found a link between the likelihood of a driver being involved in a collision and their hazard perception (HP) ability, with young and inexperienced drivers having inferior HP abilities compared to older and more experienced drivers. This thesis presents a series of studies that investigate the factors that affect HP performance as well as comparing different HP testing methods. The traditional video-based method is explored as well as new methods utilising a high-fidelity driving simulator (used as an analogue of real-world driving) in order to see if there are ways of making HP testing more representative of detecting and responding to hazards while driving on the road. This thesis also explores the use of functional near-infrared spectroscopy (fNIR) as a portable and flexible means of measuring dorsolateral prefrontal cortex (DLPFC) activity during driving. Comparisons between video-based HP testing (similar to that used in the UK HP test) and simulator-based HP testing revealed significant differences in psychophysiological and behavioural responses, indicating that video-based methods may not be representative of HP while driving on the road. fNIR was found to primarily measure task workload and to be a reliable means of recording DLPFC activity across a range of different driving tasks. The fNIR results also demonstrated that DLPFC was similar when performing a simulator-based HP test and a hybrid simulator method using simulation replays, suggesting that introducing elements of driving simulation may help bridge the gap between current video-based HP testing methods and HP while driving on the road. These findings have important implications for the theoretical and practical aspects of HP testing and the use of fNIR in driving research.

Diese Arbeit soll im Wesentlichen dazu beitragen, die Frage der Abhängigkeit von Unfallursachen bzw. beschreibenden Eigenschaften eines Verkehrsunfalls zum Alter des Hauptverursachers im motorisierten Straßenverkehr zu beantworten. Anhand der Darstellung des Unfallgeschehens in der BRD kann abgeleitet werden, dass die Anzahl der Unfälle im Straßenverkehr seit einigen Jahren langsam aber stetig steigt. Im Gegenzug sinkt jedoch die Schwere der Unfälle. Anhand der Definition verschiedener verkehrsunfallbezogener Risikofaktoren können die Unfallrisikogruppen in Form der Fahranfänger und Senioren identifiziert werden. Das Risiko zu verunfallen ist für einen 17-Jährigen Fahranfänger mehr als sechsmal höher als das Risiko der Referenzkategorie der erfahrenen Fahrer. Die Gründe dafür werden durch eine altersbezogene Unfallursachenanalyse offengelegt. Um einen Überblick über verschiedene Ansätze zur Bestimmung der Unfallursachen zu bekommen, wird neben den durch die Polizei kategorisierten amtlichen Unfallursachen und der merkmalsorientierten Dokumentation das Konzept eines verhaltenspsychologischen Ansatzes diskutiert. Es ist davon auszugehen, dass die Gründe für einen Unfall facettenreicher sind als es die Kategorien der amtlichen Statistik abbilden können. Primär wird davon ausgegangen, dass verschiedene Metaereignisse, wie zum Beispiel Ablenkung in Kombination mit einer amtlich dokumentierten Unfallursache, in einer Wirkungskette als Bedingung für ein Unfallereignis auftreten. Mit Unfällen gehen auch immer Strategien zur Unfallvermeidung einher. Präventionsmaßnahmen werden in umfänglicher Form von verschiedenen Interessengruppen formuliert und praktiziert. Wesentliche Ansätze werden zur Bewertung des Zusammenhangs zwischen personenbezogenen Merkmalen, wie dem Alter, diskutiert. Eine Clusteranalyse, als strukturentdeckendes Verfahren, von sächsischen Unfalldaten klärt, ob das Alter einer Person im Zusammenhang mit einer dokumentierten Konfiguration von Unfalleigenschaften steht und schafft dabei eine Grundlage zur Ausrichtung geeigneter Präventionsmaßnahmen in Abhängigkeit zum Alter des Hauptverursachers. Die wesentlichen in der Literaturrecherche formulierten Zusammenhänge zwischen den Unfalleigenschaften und dem Alter einer Person gelten auch für den räumlich begrenzten Unfalldatensatz. Zusätzlich konnten eine Reihe weiterer Eigenschaften als bedeutsam klassifiziert werden. Zudem ergeben sich auch für Unfallverursacher, die keiner Risikogruppe zugeordnet wurden, bedeutsame Eigenschaften eines Unfalls mit Getöteten.

During the period 1980 to 2008 there were 359 fatal accidents involving UK registered light aeroplanes of which 36% occurred in visual meteorological conditions. In all, 216 lives were lost with accidents being attributed to the pilot 'failing to maintain proper control resulting in a stall or spin'. Dissimilar fatal stallrelated accident rates are evident for aeroplane makes & models of similar design. During the course of this programme of research, flight testing of two similar aeroplane models using a case study method showed marked differences in the variation of stick force with airspeed or stick force gradient in all flight conditions. This suggested that 'control feel' was a contributory factor towards the pilot’s failure to maintain proper control. Current certification standards for light aeroplanes rely upon the subjective assessment of stick force gradients by test pilots, requiring that substantial changes in airspeed are accompanied by clearly perceptible changes in stick force with no specified minimum gradient. This programme of research has been carried out to determine acceptable criteria for stick force gradients of a light aeroplane in all flight conditions. Criteria has been determined from flight tests of aeroplanes with different in-service safety records and subjective pilot workload assessment using simulated flying tasks with different stick force gradients performed by twenty GA pilots. Simulation tests indicated that pilot mental demand increased significantly (p > 0.05) when stick force gradient was reduced to ‘zero’, representing an aeroplane with neutral longitudinal static stability. A predictive model has been developed to estimate stick force gradients for a light aeroplane in any flight condition under quasi-static, longitudinal, non-manoeuvring flight and 1-g loading conditions. The model builds upon previous published work limited to cruising flight, and enables the estimation of stick forces and gradients due to high lift devices in the climb and landing condition by consideration of the combined effects of wing loading, CG, elevator gearing, flaps and elevator trim setting. Implemented using MATLAB, the model has been validated by comparing with flight test results for the case study aeroplanes and showed mean differences of ±0.025 daN/kt. The predictive model should be used in preliminary aeroplane design to assess tendencies towards neutral stability in high workload, safety critical flight conditions such as the take-off and landing. In addition, the model should be used to analyse existing aeroplanes with comparatively low or neutral stick force gradients in safety critical flight phases and to predict the effects of changing CG and/or flap limits to increase stick force gradient and improve control feel. The combined results of these studies suggest that a minimum acceptable stick force gradient for a non-aerobatic light aeroplane in all flight conditions should be nonzero and between 0.10~0.13 daN/kt. A stable and predictable stick force variation with airspeed will ensure that any substantial deviation from trimmed airspeed is accompanied by a stick force change clearly perceptible to the pilot and also provide additional warning of the proximity to the stall. The use of specific criteria to complement qualitative test pilot opinion, will assist in confirming compliance and provide consistency with current standards for sailplanes/powered sailplanes and large commercial aeroplanes, both of which already have defined minimum acceptable gradients.