Anaerobic sludge digesters of the squat cylindrical shape have inherent flaws which drive up maintenance costs, limits its ability to maintain optimum environmental conditions and is not shaped for efficient mixing. The egg-shaped sludge digester is an effective solution to these flaws. However, the analysis of these structures are complex and design guides are not readily available to designers of anaerobic sludge digesters. In previous studies, various shells of revolution were considered as egg-shaped sludge digester geometries. In terms of stress behaviour, these studies found the geometries to be suitable to act as egg-shaped sludge digesters. This thesis extends the list of geometries explored and considers the stress behaviour in an ellipsoid of revolution. First, only the membrane stress distributions were considered by varying a parameter e (the major axis radius over the minor axis radius) of the ellipsoidal shell. To conduct the study, closed form solutions for the meridional and hoop stresses were derived. The stress distributions of the varying ellipsoidal geometries were then compared and analysed. Additionally, the parametric study considered structural efficiency of the shell. Following this, in order to judge the effectiveness of the geometry, it was compared to findings of previous studies on different geometries. The study compared the geometries on the bases of volume, smoothness and maximum hoop stresses. It was found that the ellipsoidal geometry faired extremely well against the other geometries in the volume and maximum hoop stress criteria. Due to the limitations of the membrane theory of shells to predict bending stresses at supports and other discontinuities, a finite element study was conducted to achieve a complete shell stress distribution. Special attention was paid to bending at the support region where large meridional stress peaks occur as well as bending stresses seen at the apexes. Following this, various support conditions were tested to gather a full understanding of how this affects the total stress distribution in the shell. Finally based on findings of the study a design guide for egg-shaped digesters of ellipsoidal geometry was given.

In 2015, the Ascension III water rocket shattered the previous long-standing world record of 633 m after reaching an altitude of 835 m. This feat was primarily attributed to the design of the Carbon Fibre Reinforced Plastic (CFRP) pressure vessel portion of the rocket. The pressure vessel was composed on a long, thin-walled commercial CFRP cylindrical tube that had two Poly Vinyl Chloride (PVC) end caps bonded onto either end with an adhesive. The inside wall of the CFRP tube was coated with a thin rubber liner to prevent leakage through the tube wall of the pressurised air-water mixture that provided the necessary thrust for the rocket. The outcome was that the CFRP pressure vessel design was thus, novel, low-cost and lightweight with the potential to be used in other gas storage applications for example in Hydrogen Fuel Cell (HFC) applications. This report details the research aimed at identifying the feasibility and suitability of the proposed CFRP pressure vessel concept for high pressure hydrogen gas storage for use in Hydrogen Fuel Cell Powered Vehicles (HFCPVs). The primary component of the pressure vessel to be designed was the CFRP tube which was to be commercially filament wound using carbon fibre and epoxy resin. With an angle ply laminate structure for the CFRP tube, an optimal fibre winding angle of 50° was initially chosen to maximise the burst pressure. The stress analysis and strain behaviour of the CFRP tube were modelled using the Classical Lamination Theory. Specimens were made using the same CFRP material as the tube and were tensile tested to give an initial set of approximate properties to be used in the design calculations. The distinct geometrical features of the end cap were designed, and Aluminium 6082-T6 was selected as a suitable material for its construction as it was easy to machine while it also possessed desirable mechanical properties. SpaBond 340 LV epoxy adhesive was used to bond the end caps onto the ends of the CFRP tube. A number of specimen CFRP pressure vessels were constructed with the inclusion of the rubber liner. Hydrostatic burst tests were performed on specimen vessels with different wall thicknesses (2 mm and 4 mm) to determine the pressure at which each type of vessel would fail. However, only the 2 mm vessels experienced failure of the CFRP tube section as the predominant failure mode while most 4 mm vessels failed by shearing of the interface between the adhesive layer and end cap. According to the ASME Boiler and Pressure Code Section X, the maximum design pressures at which the CFRP pressure vessels could operate at were at most, 2.25 times smaller than the respective failure pressures. The maximum design pressures were thus determined to be 147 bar and 182 bar for the 2 mm and 4 mm CFRP pressure vessels respectively. The specimen pressure vessels were also fitted with strain gauges on the external cylindrical surface of the CFRP tubes to measure the longitudinal and hoop strain during the burst tests. The strain measurements allowed the deformation behaviour of the CFRP tubes to be modelled which would prove useful for designing further CFRP tubes. For all specimen CFRP pressure vessels, it was observed that the deformation response of the CFRP tubes were linear up until a certain pressure. Beyond that point, a decrease in stiffness was observed which suggested that some form of irreparable damage had commenced. Other specimen CFRP pressure vessels were constructed and underwent hydraulic proof testing at 1.25 times the design pressure for 30 minutes and at the design pressure for a further 24 hours. The objective was to assess if the pressure vessels were durable and reliable of which all tested specimen vessels passed successfully. The hydraulic proof test results seemingly suggested that the rubber liner could adequately prevent leakage of water from the vessels at their design pressures. The long-term gas leak test was performed at the design pressure using air (i.e. a compressible fluid) on the proof tested pressure vessels to detect and localize any leaks for a duration of up to 72 hours. However, the leak rates were determined to be at least an order of magnitude larger than the recommended leak rate for hydrogen gas storage vessels. The leak test results strongly suggested that the rubber liner was insufficient to prevent air molecules from escaping the vessel, was not durable for repeated use and thus, not suitable for long-term gas storage. Therefore, it was concluded that the novel CFRP pressure vessel design concept was not yet suitable for hydrogen gas storage, but with improvements, could still prove possible for use in HFCPVs. Further work into these improvements could include improving the end cap design and testing other rubber liners.

This dissertation investigates, in the context of South Africa (SA), the process economics of energy from biogas, and hence the financial viability establishing a biogas plant in the absence of a formal incentivisation programme. Firstly, the study set out to establish an improved understanding of the costs associated with the technology. Data on the capital- and running costs of existing biogas plants in SA were sourced by means of stakeholder interviews, and compared with published data on similar plants in countries where the biogas sector is more mature. Two biogas usage pathways were evaluated: biogas-to-electricity through a Combined Heat and Power (CHP) system, and biogas-to-biomethane. Regression analysis was carried out on the observed costs, and this was used to predict future costs. A capacity-cost factor of 0.68 for biogas-to-electricity and 0.57 for biogas-tobiomethane was obtained. Statistical hypothesis testing revealed that the values are significantly smaller than 1, which indicates that economies of scale are observed in both cases. A Lang factor of 1.81 was determined, based on cost data from 20 medium- to large scale biogas plants in South Africa. Operational and Maintenance costs were determined to vary between R2.6 – R4.6 per Nm3 biogas produced where significant feedstock sorting and/or transport costs are present and R0.3 – R1.4 per Nm3 biogas produced where minimal feedstock sorting and/or transport costs are present. It was observed that energy can be recovered from biogas plants at a Levelised Cost of Energy (LCOE) of 0.5 – 2 R/kWh in SA, which corresponds with the range of 1.8 – 2.8 R/kWh documented internationally, even though the LCOE in SA is generally lower that what is observed abroad, especially at plant capacities greater than 1 MW. Based on a financial analysis, a positive Net Present Value (NPV) for a medium-cost CHP plant where only electricity is utilised as income stream is possible from 0.3 MWe upward, with greater returns at higher plant capacities. For a biomethane plant, a positive NPV can be attained at plant capacities of 4 MWeq and higher. A comparison on the financial benefits of two different biogas usage pathways revealed that a biomethane plant has greater potential profitability than a CHP plant at capacities greater than 5 MWeq, whereas at smaller capacities, a CHP plant would yield better returns. The most attractive investment scenario evaluated was a 6 MWeq biomethane plant, where a Return on Investment (ROI) of 18% could be attained with a payback period of 8 years for a plant lifetime of 20 years. However, a risk analysis making use of Monte Carlo simulation revealed that such a project will only have an 91% chance of obtaining a positive NPV, which is below the set benchmark of 95%. Considering the high up-front capital investment associated with a large scale biogas project, it is anticipated that the financial risks associated with such a project would be too high to merit investment at current conditions in South Africa. This could, however, be mitigated if an additional income stream could be established in the form of an incentive, subsidy, grant, or alternatively a waste treatment gate-fee or fertiliser sales income. Lastly, if electricity and fuel prices in South Africa continue to increase at the rate observed over the past two decades, the business case for a single-income-stream biogas plant will become increasingly attractive and profitable in the near future.

Comminution is an energy intensive, size reduction and mineral dressing process which consumes up to 50% of concentrator energy consumption. Conventional methods use mainly a combination of crushers and tumbling mills in comminution circuits. Energy consumption in these circuits has been found to be relatively high. To reduce the energy requirements, compression grinding equipment, Vertical Roller Mills (VRMs) and High-Pressure Grinding Rolls (HPGRs) have been identified as potential solutions, and they have been adopted in the cement industry. Reports from plants where these technologies have been installed in circuits indicate they are more energy efficient than the conventional comminution circuits. Studies have also suggested that the use of VRMs results in comminution products with relatively higher mineral liberation degrees. Unlike in the cement industry, comminution equipment in mineral processing circuits are also required to produce particles that can be separated and recovered in downstream processes. Froth flotation is a selective separation process that utilises differences in surface properties to separate value minerals from unwanted gangue. The success of flotation is dependent on chemistry, operational and equipment factors. The chemistry factors consider the interaction between flotation reagents and solids particles surface. The operational factors consider the effect of particle size distribution, mineralogy, feed rate, pulp density, pulp potential (Eh), bubble size, temperature and circuit design on flotation. The use of different comminution procedures may result in flotation feeds of different particle size distributions (PSDs), mineral liberation characteristics and pulp potential. Due to these differences, the resultant flotation response may differ. The present study was aimed at assessing the particle size distribution, mineral liberation profiles and the flotation response from material comminuted using the VRM floated under batch flotation conditions in a 3 litre Barker flotation cell. A complex polymetallic sulfide ore containing chalcopyrite (1.3 %), galena (2.4 %) and sphalerite (1.8 %) as the main value minerals and magnetite (68.0 %) and quartz (15.7 %) as dominant gangue minerals was used for the study. The ore was milled to target grinds of 55 %, 60 %, 65 %, 70 % and 75 % passing 75 µm respectively, at a grinding pressure of 600 kPa, air temperature of 300 K. For the benchmarking grind of 65 % passing 75 µm, the ore was also milled using heated air of temperature of 373 K and at elevated grinding pressures of 800 kPa and 1000 kPa. Further work was performed to evaluate if the VRM results are comparable to conventional dry and wet rod milling products floated under the same batch flotation conditions. An increase in grinding pressure was observed to result in an increase in throughput and a general decrease in specific energy consumption without a change in product particle size distribution nor the recovery of chalcopyrite, galena and sphalerite. Using heated air (373 K) resulted in the production of slightly less fines in the comminution products. The recovery of chalcopyrite, galena and sphalerite were not affected by the change in operating temperature. However, concentrate grade (selectivity) was compromised at elevated temperatures of comminution probably due to surface oxidation. The results indicated that the grind range to achieve the best flotation performance when using the VRM as a comminution device is between 60 % and 70 % passing 75 µm. The results also indicated that at the benchmarking grind of 65 % passing 75 µm, the specific energy consumption for comminution using the VRM was 54.3 % lower than that of the conventional tumbling mill circuit. The grind of 55 % passing 75 µm resulted in lower flotation efficiencies as the minerals were unlikely liberated enough whereas the grind of 75 % passing 75 µm resulted in poor performances due to low water recovery. Comparing VRM with wet and rod milling, the different comminution procedures resulted in flotation feed of similar PSDs for all grinds compared. The wet and dry rod milling products of grinds 55 % and 75 % passing 75 µm achieved better recoveries of chalcopyrite, galena and sphalerite as compared to the VRM performance mainly due to high water recoveries achieved. While mineral recoveries were above 90 % for the grinds of 60 % and 70 % passing 75 µm, the rod milling products had statistically better flotation recoveries at 95 % confidence compared to the VRM products. The mineral recoveries after dry rod milling were marginally better than after wet rod milling due to the minimisation of galvanic interactions during dry rod milling. For the benchmarking grind of 65 % passing 75 µm, VRM grinding resulted in 84 %, 84 % and 90 % liberated chalcopyrite, galena and sphalerite respectively. The liberation of chalcopyrite, galena and sphalerite after wet and dry rod milling were 80 %, 78 % and 90 % respectively. Chalcopyrite recovery was 96.7 %, 96.3 % and 96.7 % for the VRM, dry rod mill (RD) and wet rod mill (RW) products respectively. Galena recovery was 94.3 %, 94.3 % and 92.9 % for the VRM, RD and RW products respectively. Sphalerite recovery was 96.6 %, 97.4 % and 97.4 % for the VRM, RD and RW products respectively. The differences in recovery were statistically insignificant at 95 % confidence. Liberation differences did not translate to differences in recoveries as the ore was coarse grained. The recovery kinetics were very fast and independent of comminution procedure. Reference to the benchmarking grind therefore, the VRM can be retrofitted into existing plant installations as it is more energy efficient and the flotation performance was similar when using the flotation procedure tailored for tumbling mill-flotation systems.

The vibration serviceability of footbridges subjected to pedestrian loading has been an academic pursuit since the year 1850 (Fujino & Siringoringo, 2015). Initially, research was focussed on understanding the influence of pedestrian vertical loading on the dynamic behaviour of a footbridge. Furthermore, this loading was investigated in the context of the comfort experienced by the pedestrian on the bridge. The conclusion was that although the contribution of the vertical load is significant, synchronization and lock-in of pedestrians in this direction is difficult to achieve and thus minimal effect is imposed on the comfort of the pedestrian. More prominently, research on the lateral component of the pedestrian-induced force was conducted after the observed vibration serviceability issues on the London Millennium bridge (Dallard, Fitzpatrick, et al., 2001b). Research showed that although the contribution of the lateral component is minute (i.e 5%) (Zivanovic, Pavic & Reynolds, 2005), it is significant in its influence on the lateral dynamic behaviour of a footbridge and subsequently, the comfort experienced by the pedestrian. A valuable result from these investigations was the stability criterion (i.e the Arup model) derived by Dallard, Flint, et al. (2001). The premise of the result is that pedestrians induce negative damping to the bridge system, therefore, there exists a critical number of pedestrians who collectively induce a force which eliminates the inherent positive damping of the footbridge system and triggers synchronization or lock-in which results in excessive lateral vibrations. Consequently, excessive lateral vibrations result in diminished comfort levels. The critical number of pedestrians required to trigger lock-in is influenced by the modal dynamic parameters of the footbridge; i.e, natural frequency, modal mass and modal damping ratio. Conventionally, these parameters are presented in static form, however, this omits valuable information about the dynamic behaviour of the structure. A few advances, such as the short time fourier transform and the synchrosqueezed wavelet transform, have been made to present the modal parameters in a dynamic form. However, much of literature only presents the frequency content in dynamic form and leaving the modal mass and modal damping in static form. Therefore, the aim of this thesis was to perform crowd investigations on the Boomslang Canopy walkway, and determine the critical number of pedestrians required to trigger lock-in on the bridge using the Arup model and the vibration comfort limit method. Another aim of this thesis was to either support or challenge the convetional notion that SLE is the initiating mechanism of excessive lateral vibrations on a footbridge. The Arup model and the vibration comfort limit method were found to compute different results regarding the critical number of pedestrians. Beyond this, the obtained vibration data and the synchrosqueezed wavelet transform analysis of this data showed evidence contrary to the popular assumption that SLE is the intiating mechanism for excessive lateral vibrations. Ultimately, the results showed that the Boomslang is a lively bridge and that the potential for SLE and lock-in on the bridge is highly probable.

The supply of water is becoming increasingly strained as the demand for this essential and limited resource continues to increase. A significant amount of this resource is, however, lost through leakage. Not only does this result in a waste of a precious resource, but it also leads to a direct loss of revenue, especially considering that value has been added to the leaking water through collection, storing, purifying and pumping. A great deal of research has been done on reducing water leakages in distribution networks, however, leakage in bulk pipelines has received comparatively little attention thus far. In this study, bulk pipelines in the field were tested with a pressure testing device developed by the University of Cape Town. With this device, a range of pressures were applied to various pipeline sections and the corresponding leakages were measured, resulting in characteristic pressure-leakage relationships. The Fixed and Variable Area Discharge (FAVAD) and the empirical N1 leakage models were then applied to interpret the pressure-leakage relationships. Thirteen tests were attempted on pipeline sections ranging from 300 mm to 600 mm in diameter, and pressure tests were successfully performed on eight of the thirteen sections. Even though the effectiveness of the testing technique is dependent on the sealing capability of the isolation valves, it was found that most valves sealed effectively, with only two pipelines sections failing to isolate. The high elevation differences along the length of the pipelines were found to have a dominating effect on the characteristics of the leak, which made it possible to roughly estimate the most likely leak locations by comparing the observed leak characteristics to those found in literature for similar conditions. The dependence of the leak characteristics on the location means that both have to be determined simultaneously. This can benefit the analysis, as some locations may be excluded based on their unrealistic leakage characteristics. However, it also means that there will be uncertainty with regards to the true location and leakage characteristics for sections of the pipe where the leakage characteristics are realistic. Nonetheless, the measured leakage rate together with the estimated leak characteristics provided valuable information on the pipeline conditions, making it possible to rank the pipelines according to the severity of their conditions, for optimal allocation of maintenance resources. Through practical tests, the study shows that pressure testing is an effective, simple and low cost technique to assess leakage in bulk pipelines. It causes minimal interference to the pipe operation, requires little downtime and the data can be processed in minimal time.

Bidirectional inverters are widely applied in photovoltaic and wind systems that require battery power backup. They are advantageous over unidirectional inverters because of their ability to convert DC power into AC power and then AC power back into DC power to recharge for storage purposes. Generally, bidirectional inverters are designed to have multiple power stages and/or make use of transformers for isolation and voltage/current gain. This usually increases the cost of production and oftentimes reduces the efficiency of the system. At the same time, attempts at eliminating usage of transformers and reduction in the number of power stages limits the range of bidirectional inverters’ capabilities. This is because battery applications today require low voltage DC-AC inverters with AC-DC power flow capability to store energy for later use. As such, only buck-boost based topologies are majorly being proposed and used for this functionality. The buck boost converter is the most widely used in such applications because of its higher efficiency, low component count and simple structure. It has drawbacks, however, such as: pulsating input and output currents - this leads to lower high electromagnetic interference; lower power factor during AC-DC power flow rectification when the batteries are being recharged; and external filter is also required during this power flow to keep the charging voltage constant. This research proposes a bidirectional inverter that attempts to overcome the drawbacks of the widely used buck-boost converter-based topology. The bidirectional inverter proposed in this work is based on a bidirectional Ćuk converter. The Ćuk converter has both continuous input and output currents. A galvanic isolation option on a Ćuk converter is simpler than a buck boost converter - this is important for grid tied systems. The inverter is based on a pseudo DC-link architecture - it uses a front end Ćuk converter cascaded with an unfolding bridge to convert DC power into AC power. The switches in the converter stage are switched at high frequency, while the switches in the unfolding stage are switched slower at the grid frequency. This configuration is desirable over the two-stage topologies because the switching losses in the unfolding bridge are lower because of this low switching frequency used. This configuration also ensures good switch utilization at the unfolding stage by lowering the parasitic effects on the power transfer. The proposed inverter has 4 modes of operation: during modes I and II the power is positive, and it converts DC power into AC power; during modes III and IV the power is negative, and it converts AC power back into DC power. The inverter is designed such that during DC-AC power flow, the input and output inductor currents and coupling capacitor voltage are continuous for improved efficiency. During the AC-DC power flow, the coupling capacitor voltage is discontinuous to achieve a higher input power factor by improving the AC line current, thereby simultaneously increasing the efficiency. The inverter was analysed in terms of: the dead time inserted into the switches to avoid shoot through and shortcircuiting switches; the parasitic effects on the power transfer ratio. Because the Cúk inverter is a high order system, several robust control strategies, such as sliding mode and current control have been proposed. These control methods require complex theory and present practical challenges to be reviewed. As such a new nested loop control strategy was proposed based on the dynamics of the coupling capacitor as the primary energy storage in the Cúk inverter. The control strategy uses 2 loops: an inner current loop and an outer voltage loop. Lead compensators were designed for both the current and voltage loops to achieve good dynamic response at a high bandwidth. Both simulated and experimental results showed that the bidirectional inverter was able to meet the design specifications. The control strategy showed good dynamic response and disturbance rejection under several inverter variations. Although the efficiency during simulations was above 96%, the experimental efficiency dropped significantly because the inverter was built on a Vero board for easy manipulation. The AC input power factor was > 0.95 for both simulated and experimental results.

Sufficient energy supply is a fundamental necessity for the stimulation of socio-economic advancement. However, the current rapid rise in urbanisation has resulted in the significant increase in energy demands. Consequently, the current conventional energy supply systems are facing numerous challenges in meeting the world's growing demand for energy sustainably. Thus, there is an urgent and compelling need to develop innovative, more effective ways to integrate sustainable renewable energy solutions into the already existing systems or better yet, create new systems that all together make use of renewable energy. This research aims to investigate and establish the optimum working conditions of a feedwater heater and geothermal preheater in a power plant that makes use of both renewable and non-renewable energy resources, where renewable energy (geothermal energy) is used to boost the power output in an environmentally sustainable way. Henceforth, a simplified model of a Rankine cycle with single reheat and regeneration and another model with a geothermal preheater substituting the low-pressure feedwater heater were designed. The Engineering Equations Solver (EES) software was used to perform an analysis of the thermodynamic performance of the two models designed. The models were used to analyse the energetic and exergetic effects of replacing a low-pressure feedwater heater with a geothermal preheater sourcing heat from a low temperature geothermal resource (temperature generally < 150°C). The results of this research work reveal that the replacement of the low-pressure feedwater heater with a geothermal preheater increases the power generated since less heat is bled from the low-pressure turbine (allowing more heat energy from the steam to be converted into mechanical energy in the turbine). Applying the principle of the Second Law of thermodynamics analysis, the Number of Entropy Generation Units (EGU) and Entropy Generation Minimisation (EGM) analysis were employed to optimise the designed hybrid system. The feedwater heaters and geothermal preheater were modelled as counter-flow heat exchangers and a downhole co-axial heat exchanger, respectively. The feedwater heaters were optimised by means of the method of Number of Entropy Generation Units whereas the geothermal preheater was optimised by means of the Entropy Generation Minimisation analysis method. Owing to the optimisation of these components, the operating conditions of the boiler and turbines were secondarily improved. Overall, this research emphasises the impact renewable energy has on major power plant systems that are in operation and run on non-renewables.

The interface shear strength between geomembranes and geosynthetics is a critical factor governing the stability of slopes that incorporate geosynthetics. In order to better characterise the shear properties of geomembranes, a wide-range of shear strength friction measurements were conducted. This dissertation presents the results of a study that examined interface shear strength parameters of textured high density polyethylene geomembranes (HDPE) and textured low linear density polyethylene (LLDPE) geomembranes sheared against different geosynthetics; geotextiles, geogrid and geosynthetic clay liners (GCLs), typically used in South African landfill base liners and capping systems. Tests were performed using a modified 305 x 305 mm x 100 mm large direct shear box over a range of normal pressures of 25, 50, 100, 150, 200 and 300 kPa. Shear rates of 0.1 mm/min and 1 mm/min were used for geomembrane/ GCL and geomembrane/ geosynthetic interfaces respectively. Results indicated that LLDPE and HDPE geomembranes sheared against various geosynthetic combinations produced different friction characteristics which resulted in varying performance patterns. HDPE geomembrane surfaces mainly experienced conventional linear failure envelopes when sheared with different geosynthetics. However, LLDPE geomembrane interfaces showed that the linear failure envelopes did not always give the best representation of the shear stress and normal stress relationship for sheared interfaces. These geomembrane shear strength envelopes could be described as linear until a critical confining stress in the range of 100 kPa to 150 kPa was attained, therefore making the failure envelopes bilinear. A comparison of the linear and bilinear failure envelopes showed that a bilinear failure envelope was a more appropriate approximation over large normal stress ranges. A bilinear relationship resulted in higher interface friction angles and low apparent adhesion parameters being achieved at normal stresses less than 100 or 150 kPa. While low interface friction angles and large adhesion values were produced above the critical confining pressure. Although HDPE geomembrane interfaces indicated larger stiffness and rigidity at early shear, it was observed that LLDPE geomembrane/ geosynthetic interfaces presented larger factor of safety values when compared to HDPE geomembranes sheared against majority of the geosynthetics. These results were produced when friction parameters generated from this study were applied to practical design examples of landfill base liner and capping systems. From these observations several practical recommendations were generated to assist professionals to choose suitable materials during design.

The Gauteng Province is the only province in South Africa with two rail services, namely Metrorail, operated through the Passenger Rail Agency of South Africa (PRASA), and Rapid Rail, known as the Gautrain, operated by the Gautrain Management Agency (GMA). It is widely known that these rail services do not compete for passengers as they currently serve different markets. Based on passenger survey data, PRASA currently serves the Low and Middle Income markets while the Rapid Rail serves the Upper Middle and High Income markets. PRASA has published their modernisation plans, with a focus on upgrading the Gauteng Metrorail network in the future. It is currently unclear whether these upgrades could result in a rail market overlap between Rapid Rail services and the PRASA Modernisation services. The rail market overlap holds two scenarios, a complimentary overlap and a competitive overlap. A complimentary overlap involves one rail service integrating with another, resulting in a potential increase in patronage for both services. Such an overlap is aligned with the Gauteng 25-Year Integrated Transport Master Plan (GITMP25) vision, whereby the Gauteng public transport system is integrated across multiple modes and services and would thus promote the use of the public transport system. For this overlap to take place, the rail services should serve similar markets, different geographical nodes and integrate at key transfer nodes while not competing for passengers along corridors. A competitive overlap is one where two rail services serve similar, if not the same, markets and nodes and compete for passengers along the transport corridors. Such an overlap does not support the vision of the GITMP25 as a competitive overlap requires fully operational infrastructure for both services, only to divide existing public transport users between the two services. This form of overlap is not sustainable and does not attract new public transport users to the services. In order to investigate whether the Rapid Rail and PRASA Modernisation services will have a competitive overlap, it is necessary to understand the existing and potential future rail operators’ markets, passengers’ travel behaviour and evaluate the services’ geographical overlap. Once the overlap is identified and quantified, the results will be able to guide future transport planning to minimise competitive overlap in rail services and focus on complimentary overlap to help build an integrated public transport system for the Gauteng Province. To demonstrate this, this study evaluated the existing rail services in the Gauteng Province and defined the respective sociodemographic market segmentation and mode choice drivers. A hypothetical rail market was developed for the proposed PRASA Modernisation service, aligning with the proposed service’s upgrade plans. A Multi-criteria Analysis (MCA) tool was developed to align the Rapid Rail, existing Metrorail and proposed PRASA Modernisation rail services with their respective markets in terms of income brackets. Thereafter, MCA was used to determine the overlap in markets between the three rail services. The MCA identified that the PRASA Modernisation service would expand the Metrorail market into the Upper Middle Income category as a result of the service’s expected improvements. The PRASA Modernisation Upper Middle Income market was therefore identified as the potential overlapping market with the current Rapid Rail service. The potential competitive market overlap between the Rapid Rail and PRASA Modernisation rail services were evaluated in terms of geographical market overlap, trip pattern overlap and trip making overlap. The ultimate overlap between the Rapid Rail and the PRASA Modernisation services resulted in 12% of the overall Rapid Rail patronage. Finally, an estimated uptake of the overlapping market was developed using the quantitative mode choice drivers, namely travel time and travel cost. The weightings of these mode choice drivers were aligned with that of the Rapid Rail market and the travel time and travel cost of each rail service was normalised over an average trip distance between Pretoria and Johannesburg CBDs. The estimated service uptake resulted in 58% of the overlapping market remaining to use the Rapid Rail service and 42% of the overlapping market shifting to use the PRASA Modernisation service. However, the Rapid Rail park-and-ride facilities are used by more than 40% of the Rapid Rail passengers. Without this infrastructure at the PRASA Modernisation stations, the potential uptake of the PRASA Modernisation service from existing Rapid Rail services could be diminished from 41% to 25% due to the lack of an integrated Metrorail system with private cars. The final competitive overlapping market between the Rapid Rail and PRASA Modernisation services resulted in 3 – 5% of the total Rapid Rail patronage. The research study concludes that the competitive overlap between the Rapid Rail and PRASA Modernisation services would be negligible as these services will continue to serve different markets. It is therefore recommended for the PRASA Modernisation program to be implemented to assist in the much needed rejuvenation of the Gauteng Metrorail service. It was further recommended that the PRASA Modernisation program incorporates integrated feeder and distributor services, strengthening the attractiveness of the PRASA Modernisation service and aiding in the GITMP25’s vision of developing an integrated and efficient transport system in Gauteng.