Highway traffic operations
Highway traffic operations
Highway traffic operations are influenced by the behavior of drivers. A highway can be used by a finite number of vehicles, and the driver perceived safe distances between vehicles determine this limit. For a given speed, as distances become shorter, more vehicles can use the highway. Both the volume of drivers choosing to use the highway (demand) and the maximum volume that can be served (supply) depend on driver behavior. Congestion results from too many people attempting to reach their destinations at the same time using the same highways. The combination of demand, capacity, and certain infrastructure features (traffic control devices) determines how drivers perceive the traffic conditions. Transportation agencies strive for economical solutions to congestion that satisfy a majority of highway users.
A traffic signal installation is a power-operated device which informs motorists or pedestrians when they have the right of way at a particular intersection. The first traffic signal was installed in London in 1868 and used semaphore ‘arms’ together with red and green gas lamps. Unfortunately, it exploded, putting an end to this sort of control for 50 years. However, in 1918 the first three colored light signals were installed in New York and in 1925 they started to be used in Great Britain. At the beginning of the 1930’s an attempt at making the signals more `intelligent’, or vehicle responsive, was tried in America, using microphones at the side of the road, requiring drivers to sound their horns.
This was obviously not too popular and the first traffic detectors – electrical and pneumatic were invented. Traffic signals are now used throughout the world, using the three light signals of Green, red and amber. Also, by convention, these are normally arranged vertically with the red signal at the top and the green light at the bottom. This also helps people who are colour blind – both drivers and pedestrians to identify the differences between the lights. Traffic signals are used at intersections to reduce conflicts to a minimum by time sharing of right of way. This actually reduces the capacity of the intersection, but greatly enhances safety.
Conflicts at intersections shows the potential conflict points at the junction of two roads, both with two way traffic flows, at which all crossing and merging movements are permitted. With the provision of traffic signal control the number of potential conflicts can be reduced from 64 to zero. There is no doubt that signals are one of the most powerful tools for urban traffic control available to city authorities and their correct installation can improve both traffic flow and the safety of all road users.
In comparison to other traffic improvements, signals are also relatively low capital intensive and in recent years the advancement in informatics and telecommunications has led to a new generation of low cost controllers and systems that have made modern signaling an even more attractive and powerful tool. Essentially, traffic signals form part of the “software” of a city as opposed to the roads and bridges that are part of it’s “hardware”. As such they have the advantage of being cheap and often the disadvantage of being so cheap that no local lobby is interested in them, especially when city mayors fail to see the political advantages in changing an old signal for a new one. It is thus part of the traffic engineer’s task to prove to city authorities that a modern and well designed traffic signal system will bring real and visible benefits to the city. Conflict points at an intersection.
Traffic control devices contribute a great deal to accidents that occur in Zambia.
To Contribute to Reducing the occurrence of accidents in Zambia
To improve on the standard of traffic control devices and installations.
1- For each site where traffic signals are being contemplated, it has been discovered that normally adequate data on the traffic flows at the junction is not sufficiently collected.
What has been discovered is that the local authority in most cases they do not carry out traffic count surveys as the result, they end up installing traffic lights where they are not needed. Look at figure 1, traffic lights have been introduced at the curve. They could have been placed at more convenient site to avoid accidents with vehicles that may lose breaks and at the same time file to negotiate. 2- Traffic counts are likely to be divided into two types all day counts (normally during 16 hours of a work day) usually mid block on key roads, with the objective of defining the duration of the peak periods and general vehicle composition; and, specific junction counts carried out with the objective of providing the data for evaluation and design of the junctions. Due to not considering conducting traffic surveys the objective is not clearly known hence it was discovered that most of the junctions that houses traffic devices, do not have what is referred to as” BELL MOUTH” to allow safely turning of vehicles, lack of the bell mouth has really resulted into accidents which could have been avoided at design stage.
3- The counts should be made in periods of about 15 minutes, during at least two working days. If the counts are not similar then the counts should be repeated on another working day. A simple 16 hour survey form could look like Specific junction counts are aimed at providing the data for detailed evaluation and design. This has been in most cases overlooked. In line with the same, it was discovered that where the Local Authority ought to provide a road reserve which in most cases have been given out as plots, in some instance the same “road reserve” can be used for filter lane as the road approaches the junction where traffic devices are installed. Because of that, it was discovered that usually traffic on the sides, would want to find the way out of the unnecessary congestion thereby causing an accident.(see figure 3)
4- Traffic lights not protected. It was discovered that most traffic lights at the junctions are not secured, they are usually hit by vehicles that have lost breaking system. And again because the Local Authority takes time to repair and replace the affected device, accidents continue to escalate.
Traffic lights near chawama pick & pay
5- Sub standard Quality of installation. It was also observed that most of the works are really supervised, hence contractors will normally employ cheap means of achieving the task.
6- Separators towards the junctions (or traffic devices) have been least attended to e.g the one before arcades coming from chelston (unza), many lives have been lost.
Other one is the Kerb separator in Ndola along Blantyre avenue as one approaches the traffic lights at Shoprite in town centre , equally, it has not been attended to
Last and not the least is the stud separator in Chingola just before Total filling station along Kabundi Road just after Musonko House approximately 250m before traffic lights,this equally is not in good shape hence contributes to accidents that occur at traffic lights.
For each site where traffic signals are being contemplated it is fundamental to obtain adequate data on the traffic flows at the junction. Normally, surveys should be carried out during the peak hour periods. However, it may be important to have a broad view of the flows in the city throughout a normal working day, especially when Area Traffic Control or linked signaling are being considered, below is the suggested form to be used when carrying out traffic count
There is need to construct what may referred to as” BELL MOUTH” to allow safely turning of vehicles, lack of the bell mouth has really resulted into accidents which could have been avoided at design stage. There is need to protect Traffic lights by introducing steel barriers around the traffic lights, at least 3000mm away from the pole that is carrying traffic light. We cannot bargain with life and so, for the installation of traffic device, there is need for the Government for now to have one project “Design & install”. This project should be given to a deserving company which should be able to carry out installations and give guarantee in relation to : – (1) Quality,(2)level of accidents. There is need to have highly qualified personnel in Local Authorities so that Quality of work which involves :- installation of traffic lights,separators and generally all road furniture can be attained.
This sign and the kerbing segregate vulnerable road users and slow local traffic from higher speed through traffic. Pedestrians clearly feel safe in the segregated lane.
There is need for the Local Authority to work in collaboration with RDA. Certain works that are of low standard in towns is due to lack of supervision of the contractor by RDA and Local Authority. Attached as appendices(Apendix A & B ) are the monitoring and evaluation form which can be used for supervision of projects. There is need for the supervising Authority to come up with a Logic Framework which should critically bring out: – Goals, Objectives, measurable indicators, means of verifications and important assumptions.(see below Logic framework)
Means of verification
Goal-To improve the standard of traffic devices
1. To have a nation with minimal accidents from the current 80% to 5% by 2020
2. Improve on the functional traffic control devices from the current 40% to 100% by 2020
3. To improve the availability of essential traffic control devices from the current 30% to 100% by 2016 1. % of personnel involved in road accident reduced.
2. % of functional traffic control devices increased.
3. % of essential traffic control devices increased
1. Recorded number of accident in a particular period , taking in consideration the traffic devices
2. Inventory or asset register/and physical check.
3. Stock records of the essential traffic control device.
Government commitment, Management will(RDA & Local Authorities) and Commitment, Constant flow of funds from donors Govt commitment to release funds on time unnecessary. To avoid this problem it is essential that the engineer or traffic department has a clear set of warrants to justify the use of signals. If possible, these warrants should be approved by the local government bodies (elected and executive) so that requests for signals on sites that do not need them can be refused according to pre-discussed rules and not just on the personalized decision of the head of the traffic department.
Traffic signals may be justified if, usually two, of the following criteria are present where there is a minimum major-street/minor-street conflicting vehicle volume where there may be need to interrupt continuous flow on the major road to allow traffic to exit from the minor road without excessive delay where a minimum pedestrian volume conflicts with a minimum vehicle volume where a schoolchildren crossing is present where there is a need to maintain progressive movement of vehicles along an otherwise signaled route; and where there is a record of accidents of the type which could be reduced by the use of traffic signals.
A rough and ready set of warrants might be:
Traffic flows – when there is a minimum of 1000 pcu’s per hour entering the junction during the peak hours. visibility – when drivers on the minor road have poor visibility for judging gaps. accidents – when three or more accidents (collisions or pedestrians) are registered per year. Figure 2, for example, shows the relationship between major-road/minor-road flows and the type of control recommended at a junction in the UK. For a major road flow of 20,000 pcu’s per day and a minor road flow of 6,000, a roundabout would be a good solution for eliminating the conflicting traffic movements – if space were available. If, however, the junction is in a built-up area, then traffic signals probably represent the best solution. It should be stressed, however, Monitoring and Evaluation Form appendix “A”
STRATEGIC Objective 1:
Local Authority /RDA Intermediate Objective:
Sources of Data and Collection Methods
Frequency of Data Collection
Responsible Person(s) & Team
Definition of Key Outcome Indicators
Illustrative Timeline appendix “B” Activities to Assess
1. UNIVERSITY OF AFRICA- Road Structure and Traffic Control Device module – 2013 (extract from Road maintenance Hand Book Volume iv).
2. BENT THAGESEN : Highway and traffic engineering in developing countries
3. Cannell, A. E. R. and Kaestner, C. Some Aspects of Area Traffic Control in Semi-Developed Countries.
4. Traffic engineering acrd Control. 1983. Companhia de Engenharia de Transito -CET.
5. Department of Transport. Junction Layout for Control by Traffic Signals. Highway, Safety and Traffic Advice Note TA
6. Gardner, G, Fouracre, P.R. and Jacobs, G.D. Traffic Management.
7. SCOOT: Traffic Responsive Method of Coordinating Signals. TRRL Report 1014. Transport and Road Research
8. Willumsen, L.G. and Coeymans, J.E. Research into the Value of Area Traffic Control Techniques in a Developing Country.