Design Of Intersections For Efficient Traffic Management In A City

Transportation System has been a need all over the world and it must be easily maintainable. Initiatives have been taken over the years to achieve maintainable road transportation systems all over the world. Researches and studies are being conducted in South Africa to find ways to maintain Transportation System more especially road transportation system. South African cities still find it challenging to sustain the road transportation system regardless of the creativities. This assignment is to determine the challenges experienced by certain city in South Africa and how to improve existing transportation system. South African cities can find the simplest solutions that would contribute significantly to the needs of all road users, and that is to strengthen public transportation system and to accommodate all road users in our roads such as non- motorists/ pedestrians. Secondly, the other solution would be to introduce new information and communication stems that will reduce traffic congestion by reducing traffic volumes and that will also reduce the need for travel. This will have an impact on the environmental pollution because it will be reduced since it is caused by vehicle’s carbon emissions.

What is Planning and Design?

Planning and design can be defined as a process design which actively encourages the involvement by all users of the system. This includes pedestrians, the public, business community, community group, environmental organizations through an active public participation process conducted by the governing bodies. Transportation planning includes many steps namely:

• Forecasting of future population growth, assessing which areas may be developed and how will the land be utilized;
• Identifying the current problems in the system through data collection and surveys.
• Estimating the impact of recommended improvements in the future on the transportation and its effect on environmental features, including water through models; and Monitoring the existing conditions of the transportation system
• Developing financial plan to secure enough funds to cover the costs of implementing strategies this can also be achieved through Modeling.

Introduction

Intersection Design requires one to understand both highway and traffic engineering. There are factors that affects the operation of an intersection namely its capacity, lengths vehicles and traffic flow control. Intersection physical layout is defined by its vertical and horizontal alignment, drainage, texture of the surface and roadway cross sections. For a good design all these factors combined are required and must overpower the potential safety and operation conflicts that occur when traffic flow interact at intersections. The intersection characteristic is that pedestrians, vehicles and bicycles travelling in many different directions often share a common area at the same time. The main goal of intersections is to reduce the resulting of conflicts which are influenced by costs of construction and maintenance, simplicity of implementation and environmental factors. There four different types of Intersections, namely: Three-legged T and Y, four legged intersection with a defined crossing path, multi legged intersections and Roundabouts. The selection of a type of intersection depends on the design context because intersections differ in shape, scope, traffic control measures and channelization of degree. There are important factors that need to be considered when selecting type of intersections:

• Cost of construction;
• Type of area;
• Land use and land availability;
• Functional classes of the intersecting roads;
• Approach speeds;
• Proportion of traffic on each approach;
• Volumes to be accommodated.

The focus of this Assignment is on application of the geometric principles design and planning of a Roundabout Intersections. In the 1930sand 1940s traffic circles where constructed to operate in weaving mode but the accident rates were higher than those that occur at conventional intersections. It was then decided that vehicles should yield to the left which means that vehicles that are in the circle has to give way to those that wish to enter the circles which also resulted at heavy- flow rates hence traffic circles were replaced by conventional three- four legged intersections. Modern Roundabouts are different from traffic circles because of the way they operate and the characteristics. They operate under the rule “Yield on entry” where vehicles drive on the left and yield to the right. South Africa use the same rule except in the case of the mini-roundabout, the rule is changed by the use of the R2.2 sign which indicates the approaching vehicle to yield right of way to any vehicle which will cross any yield line before him and in the normal course of events, will cross the path of such driver’s vehicle. Therefore drivers use the approached rule of first-come-first serve which applies at mini- roundabouts where drivers will yield to the vehicles on the right. They operate by bending the path of vehicles which slows the traffic down and increase yielding. Roundabouts have fewer delays than conventional intersections and have higher capacity.

Advantages

1. Speed of vehicles is reduced compared to that for another intersection type
2. Less waiting time and crossing time can be achieved than an intersection with signals.
3. Crossing opportunity is easily judged by pedestrians.
4. The task of crossing roadway is simplified because the splitter island allows a pedestrian to cross entering and exiting traffic flows.

Disadvantages

1. Vehicle traffic is controlled by yields which means it does not come to a full stop and that is not safe especially for pedestrians who uses crosswalks.
2. A roundabout can be unease depending on the mobility, age, impairment or to be able to judge gaps in traffic.
3. Pedestrians at first have to adjust to the operation of a roundabout, this includes the crosswalks location which is behind the first vehicle stopped or 6m form the yield point.

General requirements

For roundabouts to perform safely and efficiently there are certain features to be considered:

• The layout must be marked correctly and be clearly visible.
• A roundabout has to be easily available in the road system.
• The drivers must be encouraged to enter the intersection at a low speed throughout the roundabout.
• Enough lighting for safe operation at night must be provided to promote safety and security of signal.
• Enough sight distances at all entry points must be provided so that a driver can be able to enter the intersection and also be able to observe cyclists and pedestrian.

Improved safety

Results of the investigations have shown that roundabouts are safer in control than traditional stop sign or signal-controlled intersections. The number of crashed injuries is reduced by 75 % at intersections where stop signs or signals where previously installed for traffic control, the results research made by the Insurance Institute for Highway Safety has shown that roundabouts typically achieved:

• A 37 % reduction in overall collisions
• A 75 % reduction in injury collisions
• A 90 % reduction in fatality collisions
• A 40 % reduction in pedestrian collisions.

Problem Statement

Less provision for pedestrians, passengers with special needs and non- motorist like cyclist, is a problem when planning for Transportation networks in most South African cities. Intersections are being used by vehicles, pedestrians and bicycles to travel. In most cases they share a common area often at the same time. In this project we are required to plan and design a road intersection (roundabout with four or six legs) with advanced features such as ITS features on a busy road in a city of South Africa. Also analyze the impact of the intersection on the traffic movement on the roads in the road network system. Sharing of the intersection at the same time increases the number of vehicles and pedestrians which at the end of the day adds conflict t to traffic flow.

Background of Challenge and problem

his assignment pays particular attention to the problems caused by the road transportation network which are experienced mostly by motorists and to determine the solutions to accommodate all road users and develop the road transportation network. During evaluation process of transportation network (intersection), it is important to study and understand the components that are being described as the travel chain which have to be viewed simultaneously to plan a uniform journey. Important features of universal design and universal access principles has to be considered for a process of integrating, these will support the design of an environment that is more friendly and usable for all road users including non- motorists. They aim at achieving the ability of all road users to use all parts of the road transportation system and also to have accessibility to all transportation network. To summarize, all factors that affect intersection design needs to be considered in order to ease the movement of traffic flow in the area and to promote a diverse and environmental city.

Study Area

The case study area for this assignment considered is Noordhoek Suburb in Bloemfontein City ‘CITY OF ROSES’ which is situated in the Free State province in South Africa is administrated by Mangaung Metro Municipality with a population of 256 185 (census 2011) with 60 sub places and 81286 Households.

The Roundabout location is in the center of Noordhoek suburb its traffic flow is affected by the population of Noordhoek suburb and the neighboring suburbs known as Waverly and Navalsig.

Noordhoek was analysed and found that there is a problem in traffic flow during peak hours as the existing roundabout cannot accommodate the total traffic flow from the surrounding suburbs. Also, Noordhoek has flats, educational institutions, well-structured shopping centres, recreational areas. Noordhoek is situated in the Southern East of Bloemfontein with Raymond Mhlaba (N8 access route) where road users (passenger, cars or freight) from Botshabelo/ Thaba Nchu pass by Bloemfontein when travelling to the core city of South Africa Johannesburg or Cape Town, Telman Roos Street and Wilcock Street. Due to all these Bloemfontein has advanced to be one of the top 5 cities in South Africa attracting international and local trade companies. Road transportation is a minimal component for Bloemfontein Transportation system infrastructure. Other means of transportation have resulted in Bloemfontein experiencing some challenges in its road transportation network planning and those aviation, pipeline system, freight rail and posting and shipping. The Bloemfontein central island does not make provision for non-motorized means of transportation and there is conflict between buses and private cars. The streets are congested and have no attraction at all. This makes mobility in the central island very complicated especially in peak hours. Mangaung Metro Municipality is on the approach to eliminate economic inequalities by transforming townships and introducing new public transport system to the people and new developments. That is why we chose to re-design the Noordhoek Roundabout for this assessment to find the transportation networks challenges and workable solutions for the near future as to find needs to expand the roads and try to make the intersections safe.

Methodology

Literature Study: The study road transportation network in Noordhoek has been conducted based on relevant literature to examine the various challenges of the intersection. The method focused on internet searches for the literature on the current public transport system and its access nationally. The information obtained has been mostly from resources online of previous studies conducted on the city. Personal Interviews Personal interviews were conducted with cyclist, pedestrians and motorists and organization representing them. Also, specialist in the Transportation Planning and Transportation Engineering were interviewed so to obtain extensive information on the identified problem. These interviews which were conducted yielded positive results with School learners and other non-motorist users wanting to be part of the study. As a result, a survey questionnaire was developed.

Site Investigation

The existing situation in the Bloemfontein Noordhoek Suburb was examined in terms of mobility and accessibility and functionality transportation and pedestrians. Raymond Mhlaba Rd. and other neighboring Rd. was explored if is there a proper functioning of the shared intersection/ roads between pedestrians and car users. Also street parking, traffic congestion/ flow are investigated if to check the effect of the chosen roundabout. The aim of site investigation was to inspect the functionality of city streets and intersections and to see if they serve their purpose in accommodating pedestrians and more especially those with special needs.

Analysis and Findings

Data and analysis of traffic will depend on the scope and objective of the survey questionnaire and traffic count. In simple terms analysis consists of sum of different groups of vehicles in volume count. Secondly, complex surveys may require computer to analyze traffic flow to certain journey, allocation of existing and proposed road network, traffic projections and other related operations. Manual Analysis Essential part of data collection process is to be analyzed and presented in a format that is easily understandable and quick to use. Table 4 below illustrates a simplified manual counts data analysis.

The data analysis process allowed us to obtain, among others, the following reports:

• Well-defined vehicle types and counting stations;
• Transformation of data in different formats into a common data format;
• Calculation of Traffic Growth Rates of traffic volumes;
• Production of forecasts based on historical data and growth rates.

The analysis of the summarized data uses conversion parameters that we set up, and where parameters are not defined we used default system parameters. In the calculation of traffic growth rates where data is available, the system generated growth rates and updated us the user growth rate. In this case, if we couldn’t calculate the growth rate, the system will calculates the growth rate as a percentage change in traffic volume per year per vehicle category.

Based on the collected data from traffic count and personal interviews at Noordhoek Surbubs, we came to a solution where we compare data. We found that each street that passes through a roundabout carries the different vehicle capacity. We found out that each street carries about 259 design hourly volume and more as the traffic is increasing per week. The Annual Average Daily Traffic at the roundabout is about 1036 vehicles per day. The Raymond Mhlaba Street carries about 45% of the total traffic volume that passes through a roundabout; Rudolf carries 25% of the traffic as well as the Wilcock’s Street. The Tielman Roos Street carries 5% of the traffic volume. The following formula is used to calculate K-factor based on our findings on the traffic count: K- Factor = Where DHV = Design Hourly Volume. AADT = Annual Average Daily Traffic. K-factors range from 8% to 12% that can be classified as urban area and from 12% to 18% that can be classified as rural area. Based on our calculations we found that our K-factor came out between 8% and 12% and that satisfies our assumptions. Therefore, since the Tielman Roos carries the lowest volume capacity of the traffic, we realized that it is coursing the traffic conflict to the oncoming traffic from the Raymond Mhlaba Street. The solution we have come up with was to redesign the roundabout, taking out the Tielman Roos Street and widening the shoulder lane by 0.6m.

Drawing and Design

The preferred number of legs of a Roundabout is either three or four, with the roundabout being more efficient and adequate over a range of traffic volume it performs to the outmost best with three legs with the provision that the demand of a traffic volume is well balanced with three legs. Driver comprehension can be affected with number of legs exceeding four because the roundabout is larger and higher circulatory speed will be generated probably as a potential solution in these circumstances.

Conclusion and Recommendation

Concluding in regards to our findings about roundabouts and investigation on the study area. The central island is low and that denies the drivers to have a clear visual of and understanding of how roundabouts operate. Landscaping is necessary in the central island and kuyuyu grass should be used in the center of the circle because it won’t grow taller to hinder the road user’s visual. Enough spacing and mountable usage is important in roundabouts that are located around commercial areas in order to accommodate bus-trains and semi-trailers` overhang and off-tracking distance. Small traffic circles do not achieve enough turning for controlling of speed because of the diameter of a central island is small but it can be resolved by installing small rubber humps on the marked islands. Reduced lanes of the approach of roundabouts have proven to be safer than multilane roundabouts. Roundabouts with multilane should have lane line markings in the circulatory roadway in order for the vehicles to see the path taken. Solid lines, along with lane-use arrows, can be used simultaneously to avoid incidents of vehicles changing lane within the circulatory roadway. Roundabouts should use Lane-use arrows at approaches that have exclusive turn lanes and in multilane roundabouts for improved lane use. Fixed post signage on the approach of roundabouts should be present with tolerable gap acceptance time. I recommend that Bloemfontein should use Rea Vaya Bus Rapid System (BRT) which provides a fast, safe and affordable service. This should use vice is one of the best public transportation system that uses one main routes from one destination to another. This has no effect in the traffic flow, it does not block traffic of motorists or non- motorists in any way because it uses it’s only routes. Bloemfontein needs this type of transportation system to avoid traffic gem.

The government also need to work with the banks and insurances like the Discovery Insurance good driving plan where one gets rewards for good driving. So if the road transportation system is friendly for walking and cycling and also the public transportation system is comfortable and reliable. With car owners knowing that they will get a percentage relief on their monthly installment would involve them. The government would use this by to thank motorists for using on motorized modes of transportation so to promote a sustainable and environmental friendly transportation system. For Bloemfontein masses to not use non-motorized modes is possible the only requirement is safe and comfortable streets to non-motorists.