Development of proposed priority infrastructure for minibus-taxis and peak hour traffic count data

The paratransit industry in South Africa which mainly includes the minibus-taxis is growing at a fast pace. Thus, it has become the largest mobility supplier to the urban public. In Gauteng province, the economic hub of South Africa that includes Johannesburg, Tshwane and Ekurhuleni, minibus-taxis account for 46% of all peak-period passenger trips followed by private cars accounting for 44%, while buses and trains account for a combined total of 10% of peak-period. Unlike buses which have seen the provision of priority infrastructure at intersections in the form of bus rapid transit (BRT) with priority transit signals (PTS) to improve their efficiency, minibus-taxis currently do not enjoy the same benefits. However, any efforts of road authorities in South Africa to consider incorporating priority infrastructure for minibus-taxis would be constrained by the absence of literature suggesting the ideal choices and the design analytical procedures.
This research study aims to develop and evaluate design strategies for priority infrastructure for minibus-taxis at signalised intersections. Priority infrastructure at intersections can be in form of roadway facility infrastructure such as queue-jumping lanes, shared traffic lane, exclusive lanes or can be implemented via signal control. These infrastructure types are designed to provide efficiency benefits to road users mainly public transport such as buses. The first objective of this study is to develop an approach for identifying the design strategies for priority infrastructure for minibus-taxis at signalised intersections. A qualitative data method utilising document analysis technique is used to develop a framework matrix table to show the relationship between the geometric elements and the design treatments of priority infrastructure. Two categories of minibus-taxis (MBT) design strategies are then formed: 1) design strategies that only require repurposing of the existing intersection, 2) the design strategies that require major geometric improvements.
Secondly, an analytical approach is developed to evaluate the performance of two proposed design strategies using real world traffic data. To begin with, four isolated intersections in the city of Tshwane are evaluated for feasibility of the MBT design strategies. The framework matrix analysis developed earlier is utilised to select and evaluate the design strategies associated with the four intersections. In addition, the intersections are further assessed for safety, traffic operations and cost effectiveness. Eventually, the two most effective design strategies are selected for a detailed performance evaluation: 1) a shared MBT lane to be used by through movement minibus-taxis and left-turning vehicles (MBT+LT) and 2) a dedicated MBT lane for through minibus-taxis only. The approach uses modified analytical principles from the Highway Capacity Manual (HCM) to measure the performance of the selected design strategies using peak hour traffic data. The performance measures include volume to capacity ratio (v/c ratio), average vehicle delay, and adequacy of storage length of MBT priority lanes. The performances of existing intersections are compared with the performances of intersections after implementing the MBT design strategies. In general, the results show that the two proposed MBT design strategies significantly improved the performance of minibus-taxis at intersections while slightly reducing the performance of traffic in non-priority lanes.
Lastly, using the results from the two evaluated design strategies, a sensitivity analysis is performed on the modified HCM method to determine a range of traffic volumes for which the selected design strategies are feasible. Consequently, two models are set using a modified HCM method to evaluate two typical MBT design strategies involving a shared MBT lane and a dedicated MBT lane. The models are set to measure the v/c ratios of individual lanes on the approach as a measure of performances. The models are set to measure the highest v/c ratios while varying the traffic volumes at constant values of g/C ratios. The model outputs are in the form of graphs showing the relationship between left turning (LT) traffic, straight (MBT+T) traffic and v/c ratios at constant values of g/C ratios. These charts are developed as a planning and design guide when evaluating the feasibility of signalised intersections for the two evaluated MBT priority infrastructure types.
Overall, the study provides the first detailed results supporting the viability of priority infrastructure for minibus-taxis at signalised intersections. It also gives a detailed methodology and steps that could be used by traffic engineers and planners to design and evaluate the performance of priority infrastructure for minibus-taxis at signalised intersections. The matrix framework method and graphs for traffic volumes could provide planners with a structured way to identify feasible designs for the priority infrastructure for minibus-taxis at signalised intersections. The methodology used in this study can be adopted to evaluate other types of design strategies not evaluated in this study.
The study concludes that with well optimised design solutions, it is possible to use priority infrastructure to improve the performance of minibus-taxis at signalised intersections without adversely affecting the performance of traffic in the non-priority lanes.

南非的辅助公共交通行业（主要包含迷你巴士客运班车（minibus-taxis））正处于快速发展阶段，目前已成为城市公共出行领域最大的运力供给方。在涵盖约翰内斯堡、茨瓦内与埃库胡莱尼的南非经济枢纽豪登省，迷你巴士客运班车的高峰时段客运量占总客运量的46%，紧随其后的私家车占比44%，而巴士与铁路的总高峰客运占比仅为10%。与巴士系统不同，后者已在交叉口配备以快速公交系统（BRT）结合优先通行信号（PTS）形式呈现的优先通行基础设施以提升运营效率，但迷你巴士客运班车目前尚未享有同等优待。然而，南非道路管理部门若考虑为迷你巴士客运班车增设优先通行基础设施，却因缺乏能够指明最优方案与设计分析流程的相关研究文献而受阻。
本研究旨在开发并评估信号控制交叉口处迷你巴士客运班车优先通行基础设施的设计策略。交叉口优先通行基础设施可分为两类：一类是道路物理设施，如超前排队车道、共享行车道、专用车道，或可通过信号控制方案实现。此类基础设施旨在为道路使用者（主要为巴士等公共交通载体）提升通行效率。本研究的首要目标是开发一套方法，用于识别信号控制交叉口处迷你巴士客运班车优先通行基础设施的设计策略。本研究采用基于文献分析的定性研究方法，构建框架矩阵表以呈现优先通行基础设施的几何要素与设计处理方式之间的关联关系。随后研究将迷你巴士客运班车（MBT）设计策略划分为两类：1）仅需对现有交叉口进行功能调整的设计策略；2）需对交叉口进行大规模几何改造的设计策略。
其次，本研究开发了一套分析方法，基于真实交通数据对两种拟议设计策略的运行效果进行评估。首先，研究针对茨瓦内市的4个独立交叉口，评估迷你巴士客运班车设计策略的可行性。研究利用此前构建的框架矩阵分析法，筛选并评估适配这4个交叉口的设计策略。此外，研究还从安全性、交通运行效率与成本效益三个维度对这些交叉口进行了综合评估。最终，研究筛选出两种效果最优的设计策略开展详细性能评估：1）供直行迷你巴士客运班车与左转车辆共用的迷你巴士客运班车共享车道（MBT+LT）；2）仅服务于直行迷你巴士客运班车的迷你巴士客运班车专用车道。该分析方法依托修订自《美国公路通行能力手册（HCM）》的分析准则，利用高峰时段交通数据对选定的设计策略进行性能测算。性能测算指标包含流量-容量比（v/c ratio）、车辆平均延误，以及迷你巴士客运班车优先车道的存储长度适配性。研究将现有交叉口的运行性能与实施迷你巴士客运班车设计策略后的交叉口运行性能进行了对比分析。总体而言，研究结果显示，两种拟议的迷你巴士客运班车设计策略可显著提升交叉口处迷你巴士客运班车的通行性能，仅会小幅降低非优先车道的交通运行效率。
最后，基于两种已评估设计策略的研究结果，本研究对修订后的《美国公路通行能力手册》分析方法开展敏感性分析，以确定选定设计策略可行的交通流量区间。据此，研究采用修订后的《美国公路通行能力手册》分析方法构建了两个模型，分别用于评估两类典型的迷你巴士客运班车设计策略：共享车道策略与专用车道策略。两个模型均以进口道各车道的流量-容量比作为性能测算指标。模型设定为在保持绿信比（g/C ratio）恒定的前提下，通过改变交通流量以测算最高流量-容量比。模型输出结果以图表形式呈现，展示了在恒定绿信比条件下，左转交通流量、直行迷你巴士客运班车交通流量与流量-容量比之间的关联关系。此类图表可作为规划与设计指南，用于评估信号控制交叉口适配两类已评估迷你巴士客运班车优先通行基础设施的可行性。
总体而言，本研究首次提供了详实的研究结果，证实了信号控制交叉口处迷你巴士客运班车优先通行基础设施的可行性。同时，本研究还提供了一套详尽的方法与流程，可供交通工程师与规划人员用于设计并评估信号控制交叉口处迷你巴士客运班车优先通行基础设施的运行性能。本研究构建的矩阵框架分析法与交通流量图表，可为规划人员提供一套结构化的方法，用于识别信号控制交叉口处迷你巴士客运班车优先通行基础设施的可行设计方案。本研究采用的分析方法可被推广应用于评估本研究未涉及的其他类型设计策略。
本研究最终得出结论：通过优化设计方案，可利用优先通行基础设施提升信号控制交叉口处迷你巴士客运班车的通行性能，且不会对非优先车道的交通运行性能造成负面影响。