Doctoral Degrees (Civil Engineering)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6843

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Effect of rainfall on function service quality deterioration of dark roadways and its implication for stopping sight distance.
(2019) Makinde, Opeyemi Oluyemisi.; Ben-Edigbe, Johnnie Ebioye.
Driving in the rain at night is challenging and more so if the roadway has no light. This study aims to ascertain whether rainy dark roadways would have significant influence on functional service quality reduction, and also the associated stopping sight distance implications for road users. Dark roadways are prevalent in Nigeria mainly because of poor energy management and the absence of long term sustained-energy strategic plans. The objectives are to determine the functional service quality in the presence of rainy dark roadways and compare with that taken on dry dark roadways. To that effect a rainy dark roadway impact study was carried out at four (4) selected sites in Nigeria for a period of eight (8) weeks. Based on the circumstances prevalent at the time of the survey, the study assumed that density was a result of speed and flow hence not directly affected by rainfall. This implies that functional service quality was fully the result of speed and travel time changes. Functional service quality describes the assessment of service delivery of roadways based on both road provider (travel speed) and user (travel time) perceptions. Vehicle types, volumes, speeds and rainfall were collected continuously at each surveyed road section for eight weeks and the results analysed. Traffic volume was converted into flow using modified passenger car equivalents values. The results of the analysis show reduction in travel speed with ensuing increase in travel time. Results show that the average travel time increased by 27.1 percent on dark roadways due to night rainfall. Results show that the average travel speed decreased by 18.7 percent on dark roadways due to night rainfall. The results from the analysis were used to establish the stopping sight distance implications of rainy dark roadways for motorists. Results show that on dark roadways the average stopping sight distance (SSD) increased by 25.8 percent due to rainy night. Results from the predicted travel time loss confirm the established evidence that travel time is a significant guide for measuring road effectiveness. Finally, since there is the potential to improve functional service quality output based on efficient and appropriate energy on one hand; effective management of resources on the other, the study concluded that in the presence of rainfall, dark roadways have a significant impact on the functional quality of service and stopping sight distance.
Influence of rainfall on quality of service at multilane roundabouts and its time headway implications.
(2018) Ibijola, Stephen Olukayode.; Ben-Edigbe, Johnnie Ebioye.
Roundabouts, or traffic circles as they are often called in South Africa, are priority intersections with a unique yield rule. Drivers approaching the roundabout must give way to those that are already circulating the central island. The fixed features and yield rule do not change relative to rainfall; however, vehicular flow rate and driver behaviour are often affected by ambient conditions like rainfall among others. Consequently, in this the study the influence of rainfall on the quality of service delivery at multilane roundabouts and their implications for time headways have been investigated. Based on the hypothesis that rainfall, irrespective of intensity, has adverse effects on the quality of service delivery and time headway at roundabouts, an impact study was carried out in Durban, South Africa. Entry, circulating traffic flow rate and rainfall data were collected at four selected sites in Durban, South Africa. Over one million traffic volume data was collected during the August 2016 to February 2017 rainy season. The key selection criterion is proximity to an active rain gauge. Empirical data were collected continuously for six weeks on each selected roundabout. Rainfall data were collected from surface rain gauge stations with a distance range of 0.75km – 1.18km from the selected sites. Three classes of rain precipitation intensity (i) (light rain, i < 2.5mm; moderate rain, 2.5mm < i ≤10mm; and heavy rain 10mm < i ≤ 50mm) were considered. Very heavy rain, with an intensity greater than 50mm/h, was not considered because of associated drag force and aquaplaning which might be difficult to separate from the rainfall effect. Daylight data were separated into peak and off-peak traffic periods. Peak period data were used to develop a quality of service criteria table and the off-peak data were used to determine traffic flow rate performance. Passenger car equivalent (PCE) values used to convert vehicles per hour to pce per hour was investigated for analytical suitability given rainy conditions. Entry flow rate was used as a function of circulating flow rate to model entry capacity and, hence, determine the reserve capacity. Initially, both linear and exponential models were used, in turn, to test for analytical suitability. Linear model was the preferred after exponential function failed empirical tests. Linear function was used to model the relationships between entry and circulating traffic flow rates. The ensuing entry capacity was also used in conjunction with headway and degree of saturation to estimate entry delay under dry, light, moderate and heavy rainy conditions. The impact study reasons that quality of service is not the same as level of service, hence, the criteria table cannot be the same. This is a clear departure from Highway Capacity Manual (HCM) prescription for roundabout level of service criteria table. The novel quality of service criteria table prescribed in this thesis, has delay and reserve capacity as the xxxi key determinants of service grade. It is also referred to as Functional Quality of service (FQS) in the thesis. FQS criteria table was developed for each study site and used to assess their service delivery. The criteria table was divided into six classes (A to F), where A is the best grade and F is the worst. In any case, traffic performances were analysed and results show that; i) there is no significant difference between South Africa passenger car equivalent values and those estimated in the study; ii) the novel criteria table developed in the study is an effective determinant of FQS delivery at roundabouts; iii) entry traffic flow rate rates decreased because of rainfall and by extension induced a reduction in quality of service delivery at all surveyed sites; iv) entry delay and attendant queue increased during rainfall; v) time headway increased and entry reserve capacity decreased because of rainfall. It has been concluded that rainfall has an adverse effect on the FQS and also, that heavy rainfall has the most significant impact on FQS at roundabouts. It is proposed that in future research, on roundabout entry capacity estimation based on polynomial quadratic function where the single-variable quadratic polynomial would have density as the independent variable and flow rate as the dependent be considered.
Influence of rainfall on red-light running at signalised intersections and the service quality implications.
(2021) Oyaro, Janet Kemunto.; Ben-Edigbe, Johnnie Ebioye.
When drivers approach a signalised intersection stop-line, they must decide whether to stop or proceed and clear the intersection before the end of a green phase. The driver behaviour at the intersection affects signalised intersections' performance especially in terms of safety (red-light violation) and efficiency (throughput and delay). Drivers are affected by the state of the traffic lights, prevailing traffic conditions, road conditions and prevailing yellow light laws. When rain falls driver behaviour is affected, and this could, in turn, affect the performance of signalised intersections. This study aims to determine the impact rainfall has on red-light violations and what implications that could have on intersection service quality. In Durban South Africa, four (4) signalised intersections were selected for a “dry” versus “rainy” study carried out using traffic, and rainfall data collected over eight weeks covering the rainfall season. The probability of red-light running (RLR) was found to decrease with an increase in rainfall intensity. The probability reduced from about 42% on average under dry conditions to 17% under light, 7% under moderate and 2.5% for heavy rainfall intensity. It implies that it becomes nearly impossible to violate a red light under rainfall conditions due to speed reduction and hence increase in travel time. The average time needed to safely cross the stop line at the onset of yellow time interval also increased from 3s during dry weather to 3.6s for light rain, 3.9s for moderate rain, and 4.5s for heavy rain. Thus, approaching vehicles cannot safely enter the signalised intersection and must wait at the stop line for a green signal. Therefore, it can be summarised that rainfall has a mitigating effect on red light violations especially under heavy rain where it is near impossible to run a red light. South Africa does not have a highway capacity manual (HCM) and relies on USA-HCM for signalised intersection assessment. HCM uses delay as the sole determiner of signalised intersection quality of service; this was found inadequate and not a complete reflection of driver perception of the level of service; this study proposed a criterion that incorporated degree of saturation in addition to the delay. With the developed criteria, analysis was done to determine the rainfall influence on signalised intersection performance. Through and right-turning traffic were considered separately in this study. For through traffic, saturation flow rate reduced by 3.9% under light rainfall, 8.68% under moderate and 10.88% under heavy. It led to a capacity loss of 4.25% under light, 9.18% under moderate and 11.5% under heavy. For right-turning traffic, saturation flow rates decreased by 7.07% under light rainfall intensity, 13.44% under moderate and 17.88% under heavy. The capacity loss was also recorded where light rainfall caused a 7.38% loss, moderate 14.5% and heavy 19.15%. For the degree of saturation, delay, and queue length, all three increased. The degree of saturation increased by 1.55% under light, 7.23% under moderate and 9.4% under heavy. The overall impact on service quality was mixed; for through traffic lanes, few instances where heavy rainfall caused a deterioration in SQ by one level were recorded. For right-turning traffic lanes, the results were more consistent with expectations. There was an increase in both degrees of saturation and delay. Overall, the SQ level deteriorated especially under heavy rainfall conditions. Right-tuning lanes showed higher SQ deterioration attributed to their higher saturation level.

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Browsing Doctoral Degrees (Civil Engineering) by Author "Ben-Edigbe, Johnnie Ebioye."