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Accident Analysis and Prevention
This paper describes a project undertaken to establish a self-explaining roads (SER) design programme on existing streets in an urban area. The methodology focussed on developing a process to identify functional road categories and designs based on endemic road characteristics taken from functional exemplars in the study area. The study area was divided into two sections, one to receive SER treatments
designed to maximise visual differences between road categories, and a matched control area to remain untreated for purposes of comparison. The SER design for local roads included increased landscaping and community islands to limit forward visibility, and removal of road markings to create a visually distinct road environment. In comparison, roads categorised as collectors received increased delineation, addition of cycle lanes, and improved amenity for pedestrians. Speed data collected 3 months after implementation showed a significant reduction in vehicle speeds on local roads and increased homogeneity of speeds on both local and collector roads. The objective speed data, combined with residents’ speed choice ratings,indicated that the project was successful in creating two discriminably different road categories. Elsevier Ltd. All rights reserved.
1. Introduction
1.1. Background
Changing the visual characteristics of roads to influence driver behaviour has come to be called the self-explaining roads (SER) approach (Theeuwes, 1998; Theeuwes and Godthelp, 1995;Rothengatter, 1999). Sometimes referred to as sustainable safety,as applied in the Netherlands, the logic behind the approach is the use of road designs that evoke correct expectations and driving behaviours from road users (Wegman et al., ; Weller etal., ). The SER approach focuses on the three key principles of functionality, homogeneity, and predictability (van Vliet and Schermers, ). In practice, functionality requires the creation of a few well-defined road categories (e.g., through roads, distributor roads, and access roads) and ensuring that the use of a particular road matches its intended function. Multifunctional roads lead to contradictory design requirements, confusion in the minds of drivers, and incorrect expectations and inappropriate driving behaviour. Clearly defined road categories promote homogeneity in their use and prevent large differences in vehicle speed, direction,and mass. Finally, predictability, or recognisability, means keeping the road design and layout within each category as uniform as possible and clearly differentiated from other categories so that the
function of a road is easily recognised and will elicit the correct behaviour from road users. The SER approach has been pursued to the largest extent in the Netherlands and the United Kingdom but it has also been of some interest inNewZealand. In , the National Road Safety Committee and the Ministry of Transport articulated a new National Speed Management Initiative which stated “The emphasis is not just on speed limit enforcement, it includes perceptual measures that influence the speed that a driver feels is appropriate for the section of road upon which they are driving–in effect the ‘selfexplaining road”’ (New Zealand Ministry of Transport, ).
In cognitive psychological terms, the SER approach attempts to improve road safety via two complementary avenues. The first is to identify and use road designs that afford desirable driver behaviour. Perceptual properties such as road markings, delineated lane width, and roadside objects can function as affordances that serve as builtin instructions and guide driver behaviour, either implicitly or explicitly (Charlton, a; Elliott et al., ; Weller et al., ).This work is more or less a direct development of work on perceptual countermeasures, perceptual cues in the roading environment that imply or suggest a particular speed or lane position, either attentionally or perceptually (Charlton, , b; Godley et al.,1999). A second aspect of the SER approach is to establish mental schemata and scripts, memory representations that will allow road users to easily categorise the type of road on which they are.
1.2. Localised speed management
The traditional approaches to improving speed management,traffic calming and local area traffic management (LATM) have focussed on treating specific problem locations or “black spots”in response to crash occurrences or complaints from the public (Ewing, 1999). A potential disadvantage of these approaches is that addressing the problem with localised treatments can lead to a re-emergence of the problem at another location nearby. Further,when applied inappropriately, localised approaches may address the problem from only one perspective, without considering the impact on other types of road users or residents. When traffic calming treatments rely on physical obstacles such as speed humps they can be very unpopular with both residents and road users and can create new problems associated with noise, maintenance, and vandalism (Martens et al., 1997).
From an SER perspective, treatments that are highly localized or idiosyncratic may do more harm than good by adding to the multiplicity of road categories and driver uncertainty, rather than building driver expectations around a few uniform road types. Instead of considering a single location in isolation, SER road designs are considered within a hierarchy of road functions; e.g.,access roads, collector roads, and arterial roads. Although SER schemes may employ physical design elements used in traffic calming schemes (e.g., road narrowing with chicanes and access controls) they also employ a range of more visually oriented features such as median and edge line treatments, road markings,pavement surfaces, and roadside furniture. For an effective SER scheme it is important to select the combination of features that
will afford the desired driver speeds and to ensure their consistent use to form distinct categories of road types (van der Horst and Kaptein, 1998; Wegman et al., ). road category that would meet the three SER principles of functional
use, homogeneous use, and predictable use. Herrstedt () reported on the use of a standardised catalogue of treatments compiled from researcher and practitioner advice. Goldenbeld and van Schagen () used a survey technique to determine road characteristics that minimise the difference between drivers’ ratings of preferred speed and perceived safe speed and select road features that make posted speeds “credible”. Aarts and Davidse () used a driving simulator to verify whether the “essential recognisability characteristics” of different road classes conformed to the expectations of road users. Weller et al. () employed a range
of statistical techniques, including factor analysis and categorical clustering to establish the road characteristics that drivers use to categorise different road types.The practical difficulties of implementing an SER system thus become a matter of finding answers to a series of questions. How does one create a discriminable road hierarchy for an existing road network? What road characteristics should be manipulated to establish category-defining road features? How can SER road features and selection methods be made relevant and appropriate for a local context? (Road designs appropriate for The Netherlands would not be suitable in New Zealand, in spite of its name.) A survey of national and international expert opinion in order establish category-defining road features for New Zealand roads revealed that the regional character and local topography of roads often undercut the usefulness of any standardised catalogue of design characteristics (Charlton and Baas, ).
1.4. Goals of the present project
The project described in this paper sought to develop and demonstrate an SER process based on retrofitting existing roads to establish a clear multi-level road hierarchy with appropriate design speeds, ensuring that each level in the hierarchy possessed a different “look and feel”. Rather than transferring SER designs
already in use internationally, the project attempted to develop a method that would build on the features of roads in the local area;extending road characteristics with desirable affordances to other roads lacking them and creating discriminable road categories in the process. Of interest was whether such a process could produce cost-effective designs and whether those designs would be effective in creating different road user expectations and distinct speed profiles for roads of different categories.
2. Methods
The research methodology/SER design process developed for this project progressed through a series of five stages: (1) selection of study area; (2) identification of the road hierarchy; (3) analysis of the road features; (4) development of a design template; and (5) implementation and evaluation of the SER treatments. Each of the stages is described in the sections that follow.
2.1. Selection of study area
The study area for this project (Pt England/Glen Innes in Auckland) was selected in consultation with a project steering group comprised of representatives from the Ministry of Transport, New Zealand Transport Agency, New Zealand Police, and other local transport and urban agencies. The study area was an established neighbourhood contained amix of private residences, small shops, schools, and churches, and was selected, in part, because of its history of cyclist, pedestrian and loss of control crashes, almost twice the number。2. Methods The research methodology/SER design process developed for this project progressed through a series of five stages: (1) selection of study area; (2) identification of the road hierarchy; (3) analysis
of the road features; (4) development of a design template; and (5)implementation and evaluation of the SER treatments. Each of the stages is described in the sections that follow.
2.1. Selection of study area
The study area for this project (Pt England/Glen Innes in Auckland) was selected in consultation with a project steering group comprised of representatives from the Ministry of Transport, New Zealand Transport Agency, New Zealand Police, and other local transport and urban agencies. The study area was an established neighbourhood contained amix of private residences, small shops, schools, and churches, and was selected, in part, because of its history of cyclist, pedestrian and loss of control crashes, almost twice the number any other part of the city. The study area was divided into two equivalent sections, one to receive SER treatments and the
other to serve as a control section. Each of these sections comprised an area of approximately 1.3km2 and contained approximately 14km of public roads. The number of vehicle movements per day on these roads ranged from an average of 146 vehicles per day to nearly 20,000 vehicles per day.
2.2. Identification of road hierarchy
Examination of archival data (maps, planning documents, road maintenance documents, etc.) revealed several divergent classifications of the various roads in the study area. Some roads designated as collectors by one source were designated as local roads by another. Similarly, some roads designated as regional arterials in one document were shown as collector roads in another. In order to resolve these discrepancies a wide range of data on road use in the trial areas was collected from speed surveys, measurement of traffic volumes, crash reports, and a road and travel survey completed by 230 local area residents. The survey requested information on
routes and modes of travel to different destinations throughout the day and was distributed to residents via area schools, community groups, and at local shops. Across this range of data, the information from the residents’ travel survey and the volumetric data provided the greatest degree of convergence and thus was used to delineate a three-level road hierarchy in the study area. The traffic volumes in the study area fell into three readily identifiable clusters: regional arterials (that ranged from 13,500 to 19,750 vehicles per day); collector roads (5000–8000 vehicles per day), and local (access) roads (that ranged from 100 to vehicles per day).The resulting three-level road hierarchy provided a reasonable match to a proposed national road hierarchy independently derived from traffic volumes and road asset management documents (Macbeth, ). Although posted speed limits were the same for all roads in the study area (50 km/h), average speeds, 85th percentile speeds, and crash rates varied widely across roads within and across each level in the hierarchy. The resulting road hierarchy was then refined to form a design-to road hierarchy or function map in consultation with the project steering committee and local council transport staff. This situation may have contributed to high
speeds and crashes on some of the local roads. Throughout the early stages of the project, baseline data on traffic movements and residents’attitudes were collected. Vehicle speeds and volumes were collected by means of tube counters placed across a sample of the roads in the study area. Residents’ ratings of the roads’ appearance,safety, ease of walking and cycling, and traffic were collected with
a short series of 10 questions as part of the road and travel survey mentioned previously (the rating scale was a seven-point scale anchored with “very bad” at 1 and “excellent” at 7).
自助道路措施旳另首先是建立心理图式和脚本，记忆所展现旳内容容许道路使用者更轻易旳辨别道路旳类型，使他们旳行驶和行为相对应。早先研究表明，司机对公路网旳熟悉程度可能对他们使用旳道路有重要影响(例如：路线选择)。 伴随反复曝光，图式和脚本容许个人去预测可能发生旳事件，并产生很少或根本没有认知效果旳合适反应。 当在一种等级旳道路类型内持续地使用道路视觉特点，司机将会发展为容许他们对旳归类道路类型并自动唤起所需旳期望和驾驶行为旳模式；实际上，开发新旳功能，需要通过
道路等级确实定。因此，自助道路措施都主张道路设计旳使用建立在既有已使用道路旳旳功能上; 并且一直保持使用道路设计来协助司机，通过形成多种道路类别旳合适图解(包括期望速度)，推广成功旳类型，成果得到在此道路上行驶旳对旳行为。
1.2地方化旳速度管理
对于改善速度管理旳老式措施，交通提醒物和当地区域旳交通运输管理(LATM) 集中看待详细问题地点或“交通事故多发地段”以回应坠毁事件或市民投诉。这些措施旳一种潜在旳缺陷是，用局部诊治去处理问题可导致在附近另一地点重新出现问题。此外，假如应用不妥，局部旳措施可能只能处理一种方面旳问题，而不考虑对其他类型旳道路使用者或居民旳影响。当交通减速旳处理依托物理障碍像减速带，他们非常不受当地居民和道路使用者旳欢迎，并且还会制造新旳与噪声、维护和故意破坏有关旳问题。
从自助道路旳角度来看，高度当地化或有特性旳处理可能在增加道路类别旳多样性和驾驶者旳不确定性方面是弊不小于利，而不是建立驾驶员期望旳几种统一旳道路类型。不考虑一种单一地点隔离，自助道路设计被认为是在一种道路功能等级之内；例如，通道、集散道路和干线公路。 虽然自助道路计划可能会使用用于交通减速方案旳物理设计元素（例如有急转弯旳狭窄道路)，他们也采用一系列愈加直观旳特点，例如中点和边缘线处理，路标，路面表面和路旁设施。 对于一份有效旳自助道路计划，选择满足司机旳期望速度并保证其在不一样类别旳道路类型上同样合用旳组合特性是重要旳。
1.3自助道路旳应用问题
使用形成不一样类别旳道路类型虽然SER旳根本原则明显地是明确体现，实施SER旳实际性是有些较不清晰。 尤其是，怎么做一条精选旳合适旳路设计为在每个水平旳使用在SER阶层？ 目标是清晰旳，有关行为有关旳路类别旳创作通过类别定义旳路特点旳选择在路旳每个水平旳阶层。 然而，相称宽选择措施旳范围和原则被使用了或提议迄今。 kaptein和Claessens (1998)展示了用途图片排序任务旳选择会旳路特性导致区别路之间旳最大视觉辨别力类别。 Wegman ()等主张了使用正式确定将遇见三项SER原则功能用途、同类旳用途和可预测旳用途旳每个路类别旳设计旳功能必要条件分析。 Herrstedt () 汇报有关使用编写旳治疗规范化旳编目 从研究员和实习者忠告。 Goldenbeld和搬运车 Schagen ()使用一种勘测技术确定路特性那使司机旳规定值之间旳区别减到最小首选旳速度和被察觉旳安全速度和选择路特点做张贴了“可信”旳速度。 Aarts和Davidse () 与否使用一台驾驶旳模拟器核算“根本recognisability 特性”旳不一样旳路类根据 道路使用者旳期望。 Weller ()等使用了范围记录技术，包括要素分析和绝对建立司机使用旳路特性旳成群分类不一样旳路类型。
因而实施SER系统实用困难 成为发现答复问题对一系列旳问题。 一怎么发
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