Douglas J Wilson

A Review of the Evolution of Shared (Street) Space Concepts in Urban Environments

Abstract This paper aims to clearly establish the origin and evolution of the shared space concept from a New Zealand perspective by reviewing the literature in the disciplines of both urban design and transportation engineering. The review process involves investigating the use and function of a public road space in the context of the changing of public expectations and how this can relate to a number of interconnected street design approaches (e.g. traffic calming and self-explaining roads (SERs)). These approaches have been used to minimise the influence of motor vehicles since the beginning of the automobile era. The shared space concept, when applied in public road environments in activity centres, has increasingly been embraced by urban planners, transportation engineers and regulatory agencies. A shared space diverges from a conventional road where all road users are encouraged to legitimately occupy the same road space with little physical separation. To achieve this in a safe and efficient manner, the design aims to reduce the dominance of the motor vehicle by promoting pedestrian and cycling activity and utilising the road space as a ‘place’ in addition to its ‘transport’ mobility and access purposes. Given the fundamental conceptual differentiation between a traffic-calmed street and a shared space, the paper argues that there are certain design elements, constituting a shared space, and without them, it would be difficult for a public street to function as a genuine shared space for all road users.

Analysis of Pedestrian Performance in Shared-Space Environments

The concept of shared space as applied in an urban road environment aims to reduce the dominance of motor vehicles by promoting pedestrian and cyclist activity and utilizing road space as a place. Unlike a conventional road, a shared space encourages all road users to legally occupy the same road space with little physical separation. The paper presents pedestrian-related performance measures that were developed under a multifaceted methodological framework to evaluate the success of shared-space schemes on the basis of study areas in the city center of Auckland, New Zealand. Analysis of the data before and after implementation revealed a positive result for pedestrian performance across all sites on the basis of a 24-h pedestrian profile, pedestrian trajectory, dwell time, and stationary activity. A comparative analysis of the data after implementation highlights the importance of the active frontage in enabling a lower (vehicular) speed environment in relation to the number of pedestrians within the shared space. The reported research analysis forms part of a doctoral research study at the University of Auckland with support from Auckland Transport, a regional transport agency in New Zealand.

The skid resistance performance of natural New Zealand aggregates using a dynamic friction tester

Abstract Research has clearly shown that as the skid resistance of a road surface decreases, the road-based transport crash rate increases. In recognizing the importance of providing safe pavement surfacings for travel during wet weather, most highway controlling authorities in developed countries have skid resistance standards. However, recent research has demonstrated that there is significant variation in performance between natural aggregates where supposedly high-quality surfacing aggregates (as measured by the Polished Stone Value Test) have not performed well or predictably over an economic asset life in areas of high demand for friction. A comparison is made between the performance of six natural aggregates (greywackes, felsic volcanic rocks and basalts) used in New Zealand as road surfacing dressing. The comparison includes surface friction test results of prepared samples that have undergone accelerated polishing using a new laboratory test method. The coefficient of friction is measured at various stages of polishing by the Dynamic Friction Tester. Scanning electron microscope (SEM) photographs show the characteristics of the microtexture of the aggregate surface before and after accelerated polishing, correlating the degree of surface polishing to the measured skid resistance performance and relating this to the aggregate mineralogy, grain size, and degree of lithification and diagenesis.

Safety Performance Study of Shared Pedestrian and Vehicle Space in New Zealand

Road users in a shared space are expected to travel at low operating speeds or very near walking speeds. This expectation is to ensure that an urban street functions as a destination and that the dominance of the vehicular traffic is neutralized. The implementation of a shared space concept on a public road requires a safety evaluation, especially for vulnerable road users such as pedestrians and cyclists. However, the evaluation is difficult because of potential traffic conflicts across the whole road corridor (public right-of-way) except for the designated areas that are free of vehicles. This study explored the results of a safety analysis of a shared zone in Auckland, New Zealand. Along with the recorded crash history, the before (2010) and after (2011 and 2012) data were systematically collected with video surveys and traffic counters. The vehicle speeds, volumes, and road user interactions were processed and analyzed. The outcome of the vehicle speed study highlighted the need for traffic calming to be incorporated into the shared space design to restrain vehicle operating speed, especially for off-peak periods. Further, this study challenged the traditional notion and application of the continuum of traffic events in which potential conflicts (termed inter actions in this study) and uninterrupted passages were the foundation of the number of injury or fatal crashes, specifically in a shared pedestrian and vehicle space environment.

Comparing Results between the Repeated Load Triaxial Test and Accelerated Pavement Test on Unbound Aggregate

AbstractUnbound granular materials (UGM) are extensively used as basecourse materials around the world as they are capable of bearing relatively high traffic loads and are an economical option in comparison to bound materials. The unbound materials performance as basecourse determines the life-cycle costs of a pavement. The extent to which the repeated load triaxial test can predict the performance of unbound granular materials in the laboratory is an important parameter for road designers. Moreover, the performance of the unbound basecourse materials depends upon the moisture conditions when they are being loaded, gradation curve of the material, in situ density, permeability, and the nature of the aggregate fines (clays). There is a need to find the factors that cause the variation in the performance of the materials both in the laboratory and in-field pavement conditions to enable appropriate selection and use. This research utilizes accelerated pavement tests (APT) alongside repeated load triaxial (RL...

The effect of moisture and relative proportions of clay minerals (smectite, chlorite and illite) on the performance of unbound granular base course (UGM)

An increase in moisture accelerates the deterioration of a pavement and this is especially so for unbound granular materials below the pavement surface. One of the possible reasons for this accelerated deterioration can be the mineralogical makeup of the aggregates, which can include clays. This research paper discusses the effect of the relative proportions of clay minerals on the performance of different base course materials in repeated load triaxial (RLT) tests considering moisture variation. The materials selected for this study were sourced from greywacke sedimentary rocks from both the North and South Islands of New Zealand. The mineralogical makeup of the clay content present in the base course materials was determined by X-ray powder diffraction (XRD). The performance of these materials was further tested in RLT tests at different moisture and drainage conditions. The results of the XRD and RLT tests showed that aggregates with high relative proportions of smectite clay minerals can decrease the load-bearing capacity of the base course material when moisture is introduced into the pavement materials.

Permanent Strain Behavior of Marginal Granular Material

To better understand the marginality of marginal granular materials (i.e., an aggregate that does not fully meet a premium quality specification), this study investigated the permanent strain behavior of two granular materials with different geological and mineralogical characteristics under repeated loading and different moisture conditions. The secant permanent strain rate and shakedown approach were used to analyze the permanent strain behavior of the materials. A one-dimensional swelling test was used to explain the mechanism of the permanent strain behavior of the soaked materials under repeated loading. The results show that compared with a New Zealand premium quality aggregate, the marginal aggregate exhibits a more significant increase in the cumulative permanent strain and the secant permanent strain rate after the 4-day soaking process. The results of the shakedown approach illustrate that the marginal aggregate performs reasonably well to resist permanent deformation in a dry condition, but the performance will considerably deteriorate when in contact with water under high stress. This change is a result of the presence of swelling clay minerals (e.g., smectite) in the marginal aggregates. The result of the one-dimensional swelling test indicates the high swelling potential of marginal aggregate, which provides an explanation for its poorer resistance to permanent strain. The marginal aggregate gains undesirable internal lubrication when surrounded by (moist) swelling clay mineral particles; thus, its shear strength reduces and permanent strain rate increases under repeated loading.

Correlating Laboratory Test Methodologies to Measure Skid Resistance of Pavement Surfaces

The skid resistance performance of surface aggregates can be assessed in the laboratory with a polishing device that is designed to simulate traffic polishing actions, coupled with a skid resistance measuring device. The standard laboratory test has historically been the polished stone value (PSV) test, as specified in British Standard EN 1097-8:2009. However, as the technology has advanced and traffic volume and composition on the roads have changed, other devices and methodologies have been developed in an attempt to provide better assessment of the skid resistance performance of surface aggregates. This study compared two alternative laboratory tests, the Auckland pavement polishing device (APPD) and the Wehner–Schulze (WS) devices, in assessing the skid resistance performance of three New Zealand greywacke aggregates. This paper discusses the variations in APPD and its corresponding skid resistance measuring device, the dynamic friction tester (DFT) and the effect of macrotexture in the APPD-DFT test. The results demonstrate a good relationship between the APPD-DFT and PSV tests and no relationship between the WS and PSV tests. However, the APPD and WS tests correlate well. The study used only three greywacke aggregates; therefore, no conclusive results can be drawn on the relationship between these laboratory tests as yet.

Use of the Shear Box Compactor for Porous Asphalt Mix Property Assessment

The most commonly used compaction methodologies for specimen preparation for the assessment of porous asphalt (PA) mix properties are gyratory and Marshall. Even though several individual blocks prepared by one of these test methods are usually considered to be replicates, the heating and handling histories are never identical as these are individual specimens prepared at different times. In contrast, the Shear Box Compaction (SBC) technique allows fabrication of a single slab, at a given time, which is then used to extract multiple specimens that can be considered as true replicates. The SBC can offer significant advantages in preparation of PA specimens for various tests typically performed on gyratory or Marshall specimens. The recently released ASTM D7981-15 test method on SBC of asphalt mixes is written around compaction of dense-graded (DG) mixes, not PA mixes, even though the specific mix type is not stated in the test method. Furthermore, there is a very limited literature on the SBC, with most of the published work focusing on DG mixes. This paper aims to address this gap. In this study, the SBC was used for PA mix compaction with a nominal maximum aggregate size of 10 mm using two different types on aggregates and four bituminous binders. Slab preparation and specimen extraction methodology developed were discussed in details. Variation of the air voids (AV) between the replicate specimens extracted from one slab were within ±0.5% from the average AV value regardless of the aggregate or binder type, or slab height. The total variation of AV in all the 64 extracted specimens tested was 1.9%. This gives the confidence that performance testing such as Dynamic Modulus testing, which requires very stringent control of specimen dimensions, uniformity, and AV consistency among the replicate specimens, can be performed reliably on PA. Also, some recommendations were provided on the changes needed in the ASTM D7981 for PA compaction using SBC.

The Use of Automated Flocculation Titrimetry and SARA Analysis to Predict the Performance of Bituminous Binders in Asphaltic Hot Mix and Bitumen Emulsions

Bitumen is complex chemically, but its composition determines rheology. The Strategic Highway Research Program 1 (SHRP) developed a bitumen microstructural model that relies on the thermodynamic compatibility of the fractions (based on polarity) to create a thermodynamically stable continuum. This stability determines the performance of any bitumen in hot-mix and emulsion applications. Automated Flocculation Titrimetry (AFT) developed by the Western Research Institute (WRI) USA measures Heithaus parameters that define this stability. Chromatographic analysis, known as SARA (saturates, aromatics, resins and asphaltenes) provides a broad compositional analysis that may be used with hiethaus parameters to predict the performance of bitumen in mixes and emulsions. The methodology is based on work from the Western Research Institute at the University of Wyoming Laramie (USA) to measure the known Heithaus (stability) parameters accurately and reproducibly and is detailed in ASTM 6703. In this work, Reclaimed Asphalt Pavement (RAP) binders and virgin binders were examined by SARA analysis and AFT. The properties of the mixes made with these binders are determined and compared to the predictions. A set of emulsion binders with different SARA analysis were also examined for emulsability and the results compared to the AFT results.