Abstract
Traffic has been experiencing a major boom in the recent past. This is because as economies progress, more and more people become rich and wealthy. Therefore as the populations make more wealth, they are able to buy luxurious goods and services. Automobiles are an example of the luxuries accompanied by wealth accumulation. Traffic irregularities have been on the rise especially in developing countries. This is partly because systems and policies have not been able to accommodate the increase. The number of accidents and traffic jams recorded in developing countries exceed by far those recorded in the Western world which is considered to have developed (Chitere, P & Kibua, T 2004)..
This reports studies the characteristics measures and methods that can be put in place so that these situations are minimized. The report involves considerations based on past studies which reveal certain characteristics of intersections. Roundabouts and signalized intersections are studied according to particular parameters. The results are tabulated and used to infer particular phenomena. The report mainly analyses roads in the developed world. It tries to study how two-way intersections vary in particular attributes when compared with roundabouts.
Safety is a major factor which must be considered in the transport sectors. In many countries, departments dealing with transport have been able to come up with policies which aim at ensuring safety of motorists, pedestrians and bicyclists. That is why major intersections which are signalized are being quickly transformed to roundabouts (Welter, 2010).
Acknowledgement
I would like to acknowledge Professor (insert name) for her guidance and support throughout the preparation of this technical paper. I would also like to thank (insert name) who provided the resources to assist me with data gathering.
Introduction
The world has been experiencing an increased rate of motor vehicle manufacturing in the last few decades. Countries which manufacture motor vehicles have been increasing their sales. On the other hand, countries that do not manufacture machinery have experienced a high demand of the same. Thus, due to the increase in output of automobiles, traffic has been experiencing an increasing trend.
All large cities in the world have been experiencing traffic jams. The situation may arise due to an accident involving automobiles and pedestrians. It may also include cyclists. Traffic jams can also occur because the number of vehicles has increased beyond the capacity of the road. Some roads may not have the ability to contain a particular rate of flow of traffic. Such roads may have fewer lanes. Thus traffic may build up thereby causing vehicles to move at a very slow pace.
Due to the problem of traffic, efforts aimed at reducing it have been in operation for a long time. Thus roundabouts and signalized intersections have gained wide usage of late. Roundabouts and signalized intersections are places where vehicles can stop and wait for guidance as other motorists do the same.
The issues of roundabouts and signalized intersections have attracted enough attention from the parties concerned. Many criticisms have been put forward concerning many factors that affect smooth traffic flow. This issue is widely covered in this report. It is becoming more and more agreeable that as traffic jams increase, traffic lights and roundabouts should be modified to accompany the changing conditions. For this reasons, the use of these two methods has been universally recommended as the major methods for curbing transport problems.
Roundabouts
A roundabout is a place where motor vehicles pass round a centralized region before they assume their directions. The movement may be clockwise or anticlockwise depending on the prevailing traffic rules of the country. Motorists who enter or exit a roundabout ought to consider other vehicles, cyclists and pedestrians. Thus motorists are advised to slow down as they approach a roundabout. Motorists are also advised watch for signs along the road so that guide for or against particular movements. Before entering the roundabout, a motorist should ensure that there is a huge gap in the traffic. Vehicles should move in the direction of the prevailing traffic rules i.e. keep left or keep right.
Other factors to consider include no stopping while in the roundabout, no overtaking, one must use their turn signal whenever they want to change lanes or when exiting the roundabout (Washtenaw County Road Commission, 2007). It should also be noted that whenever a motorist misses their exit, they are advised to go round again until they return to their point of exit. Pedestrians and bicyclists should always be given priority (California Department of Transportation, 2010).
Signalized intersections
On the other hand signalized intersections are places which contain traffic lights that guide a motorist, a pedestrian or a cyclist on what to do once they reach the place. The main purpose of this kind of intersection is to control the flow of competing traffic which comes from different directions. Motorists are also advised to slow down when approaching the intersection, to give priority to bicyclists and pedestrians, and watch for signs that may guide them while approaching the signalized intersection. Each motorist should also consider other motorists around them so that inconveniences should not be caused.
Many studies conducted have used SIDRA as a major tool of manipulating and analyzing data collected. The elements of the data collected can range in values. However if this data is manipulated accordingly, analysis can be drawn and major factors crystallized out in order to identify anomalies and disparities.
Comparison of safety in a roundabout and in a signalized intersection
In the recent past many studies aiming at revealing the characteristic phenomena at roundabouts and signalized intersections have been conducted. Many results have been analyzed thus coming up with particular inferences. This study tries to examine particular properties regarding certain parameters in the two situations. These parameters are safety, volume, delays, proportion stop and queuing. They are therefore discussed below.
Safety in signalized intersections
Safety in intersection has been compromised by several incidents. There have been several crashes that have occurred at signalized intersections. Most of these incidents have actually occurred in the urban areas. For instance statistics reveal that the national percentage of intersection fatalities in the urban areas of the U.S stood at 61% and 39% in the rural areas (FHWA, 2007). According to the same source, intersections recorded high fatality incidents of 21%, while roadway departures recorded fatality incidents of 58 %. Other causes of crashes on the U.S roads are pedestrians who recorded a frequency of 11% and speeding 32%. 39% of the total fatalities which occur in urban areas take place at signalized intersections.
According to the U.S Department of Transportation there are around three million intersections in the United States of which about 300,000 have signals. Hence roughly about 10% of total number of intersections in the U.S is signalized. Despite them being signalized they constitute a third of the total number of the national fatalities. Due to this high prevalence of signalized intersection fatalities, numerous resources have been availed to transport and traffic engineers so that they can be able to analyze the signalized intersections for fatality incidents. The information is also available on the web.
The other point worth noting is that the types of crashes at signalized intersections are different compared to those at other intersections. They are right angled crashes, rear end crashes, left turn crash, sideswipe and pedestrian or bicycle crashes. It is advised that drivers should acquire the concept of positive guidance where they are given information in a format which they can read, comprehend, and respond to this information in a quick way. This will reduce the chance of crashes at intersections. For instance, it is quite important for the driver to get the correct information on how to go about complex meetings of roads like an intersection.
Safety in roundabouts
Roundabouts have been in on the increase in number because countries have come to recognize that they are safer. For instance, France increases the roundabouts on its road at a rate of 1000 per year (Scrase, 2010). The major reason for France’s action is the positive impact roundabouts have on the roads. Thus for 20 years France has been able to increase its roundabouts from a mere 500 to more than 30,000.
In Nantes, for every 1000 road users, there are two roundabouts. These figures show the preeminence roundabouts have had as a major way of curbing road accidents. The principles governing the safety of roundabouts should reflect the modern standards of understanding road safety. In so speaking, roundabouts need to be simple so that drivers can be able to understand how to navigate through with much ease.
Large roundabouts with several lanes have been reporting more accidents than small roundabouts. As a matter of fact, France has been designing small and simple roundabouts. Most of the roundabouts are single lanes. As a result 80% of its roundabouts have never seen an accident (Scrase, 2010). This is attributed to their simplicity in design which helps drivers to understand. For this reason, France has recorded 20,000 accidents in its 30,000 roundabouts over the past 14 years. This is quite commendable.
Research into this issue has been able to reveal that modern roundabouts provide the safest form of intersection control available (LHTAC, 2010). Modern roundabouts have been shown to greatly reduce accidents, and reducing also the severity of the accidents. These roundabouts have also been able to reduce congestion of traffic and raise capacity. Thus transport departments need not conduct further research to establish the positive impacts and the benefits of modern roundabouts.
Roundabouts are known to slow traffic. This makes it possible for pedestrians to cross the road. On the other hand it also keeps the flow of traffic as pedestrians cross thus traffic will not become congested (Reid 2010). According to reports done in the United states, a pedestrian will have less chance of being hit by a motorist traveling at a low speed. A pedestrian will have a higher chance of being hit by a motorist traveling at a higher speed.
However when viewed in the other perspective, the slow movement of traffic can slow down emergency trips. Such trips include trips to hospitals and other rescue trips. Thus before building a roundabout, its effects to both parties i.e. pedestrians and motorists should be thoroughly investigated so as to attain equilibrium.
Thus in a particular study in Manhattan City, Kansas, it was revealed that a signalized intersection recorded an average of three crashes per annum. However, when roundabout was built in this particular two-way signalized intersection, the intersection has recorded no crash at all. In the United States, an average crush cost the economy a whopping $87,833 dollars (Luttrell et al., 2000). Thu roundabouts can be used to prevent this economic loss effectively.
Comparison of different traffic characteristics in both situations
Signalized intersections operate in such a sense that traffic crosses a particular intersection in a time cycle. Therefore it will largely depend on the distance of the queue rather than on the number of vehicles. So for instance if the signal phase for each leg is about 25 seconds, and the whole cycle about 140 seconds, and if the queue is 180 yards, the last vehicle will only be able to cross at the next cycle. This is because by the time the cycle ends, it will be about 30 yards away from the intersection.
A study was done to compare the operation of roundabout and two-way stop signalized intersection. This research was done in the United States’ city of Manhattan in Kansas. It was done by a Kansas state University research team. They performed this study on the first and newly built roundabout in this state. This study was also compared with another study at a signalized intersection. Queuing, delays, proportion stop, and some other factors were being compared in both situations (Luttrell et al, 2000). A computer model called SIDRA was used to evaluate different traffic conditions. At the Manhattan signalized intersection where the roundabout was installed, traffic accidents averaged 3 crashes per year. This roundabout controls four legs of intersection each having two lanes.
Traffic volume
This particular study at the Manhattan roundabout summarized its characteristics relative to hourly entering traffic volumes. The roundabout carries traffic at the bottom end of the range of the U.S roundabouts. Thus according to studies, the average hourly entering rate for this particular roundabout is 310 vehicles (Luttrell et al, 2000).
According to this study which also compared two-way signalized intersection whose hourly rate averaged 340 and 328 respectively, a conclusion was made in favor of roundabouts. Thus statistically speaking, roundabouts operate better than the signalized intersections in terms of traffic volume.
Queuing in a roundabout and at signalized intersection
The same study examined queuing as a characteristic parameter in both the roundabout and two-way intersection which has signals. The statistical results were tabulated with several parameters as follows.
Table 1 -95% Queue.
The 95% queue values ranged according to the table overhead. As evidenced by the table, queuing is comparatively more enhanced in a two-way signalized intersection than in a roundabout.
Comparison of Delays in both situations
Delays in two way intersections are more profound than those in a roundabout. As it has been described above, intersections largely depend on time factor other than the volume of traffic. The way a roundabout operates determines the way delay values vary. Generally speaking, roundabouts do not bias any approaches to delay. Thus roundabouts usually give each side equal delay time. The study by Kansas state university at the Manhattan roundabout tabulated the results as follows. The average vehicular delays and maximum vehicular delays were studied and tabulated.
Table 2-Average Vehicle Delay.
Table 3 – Maximum Approach Average Vehicle Delay.
According to these statistics, it is revealed that signalized two-way intersections operated with higher average vehicular delays than roundabouts, for both traffic levels.
On the other hand, controlled two way stop intersections give one street a bias against the other. Thus prolonged delays are commonly experienced in signalized intersections. However if the street which is free flowing has a huge volume of traffic, this bias can work so well in favor of this street. Hence according to this study there is a disparity in the delays in the streets of a two way signalized intersection. This disparity does not exist in a roundabout.
Proportion stop
Proportion stop is a measure of the amount of vehicles stopped by other motorists who are in the intersection as a proportion. The table below summarizes the results of the study by Kansas State University.
Table 4-Proportion Stopped.
Table 5- Maximum Approach Proportion Stopped.
According to the study all the values of the roundabout are between the two parameters of signalized intersections. The maximum proportion stopped values were not normally distributed. For this characteristic therefore, the analysis shows that roundabouts operate with low values compared to signalized intersections.
Case study of the effects of a change from signalized intersection to a roundabout
As it has been discussed in this report, roundabouts have more advantages than signalized intersections. The change from using signalized intersections to modern roundabouts however is usually met with a lot of opposition by the status quo. In the United States for example, the public has been reported opposing any imminent changes by the Department of Transport in several states. For instance, James Bennet recalls when he was the Design project manager of District 2 Roadway (CTC & Associates LLC, 2002).
Bennet begins his story by recalling how the public opposed him. He was designing a single way modern roundabout in Live Oak, northeast Florida. The roundabout is located at a five leg intersection. The intersection was well known for its long delays because it was also signalized. During the construction of the roundabout in 2000, the intersection functioned as a circular intersection for several months. Apart from a few negative comments on the project, Bennet didn’t suffer much opposition.
First of all the location was favorable. The users of this roundabout are commuters who daily use the roundabout. The Florida Department of Transport started the planning. Bennet had a couple of PowerPoint presentations he showed to the local government. The roundabout was expected to have some delays during peak hours. Thus he made it known well before that these delays will be present notwithstanding.
Drivers had to be taught how to use the roundabout. This was done by demonstrations especially to school drivers. When the roundabout project was completed, everyone including those who were against it was happy with the work. Apart from reducing delays, the roundabout offers good scenery for any driver who drives round it. Crushes have since reduced. Many studies that involve the use of software such as NetSim (network simulation) have revealed that building a modern roundabout can help manage traffic far much better than increasing the lanes of a signified intersection.
The major setback in changing signalized intersections into roundabout is the status quo. The public just wants their signal. Thus they will not accept easily the facility to be changed into a roundabout. In many parts of the United States, more and more roundabouts are replacing intersections to reduce crashes, delays and other inconveniences.
Remediation measures
Measures are being put in place to reduce these incidents. The measures include getting quantitative results from research and implementation of countermeasures. Due to the alarming number of accidents occurring at signalized intersections, careful thought has to be given on factors such as location of traffic lights and how they will operate. Thus proper signal designs should be developed so as not to have an adverse effect on safety.
Thus traffic managers should give priority to the above factors in order for the fatalities to decrease (Bared 2010). Low cost measures include improving signal timing and signs whereas higher cost measures are separation of grade or even reconstructing intersections. Some remediation measures may only apply to high volume intersections. Pavement markings can also be used to delineate travel lanes in places where there are wide intersections.
Understanding signalization should also be a key issue that needs to be factored out. Traffic engineers should device ways in which proper system of signalization is applied to a particular intersection. For instance, traffic engineers are faced with the challenge of factoring out whether they should use a pretimed signal which operates in a fixed cycle or an actuated signal which matches the length of the green light with that of the traffic demand. Thus the engineers should be able to conduct a safety performance study whereby the average annual daily traffic is analyzed together with the safety performance function.
Conclusions
In conclusion, the study has been able to show that roundabouts are better ways of managing traffic than signalized intersections. The advantage of roundabouts is that they are capable of reducing traffic congestions. Long queues of motor vehicles are greatly reduced. This is of great advantage to motorists, pedestrians and bicyclists and the government. It reduces the number of accidents on the roads.
By reducing the number of fatal accidents which cause death, it reduces the amount of money a state loses when it loses people by road accidents. It is worth noting that the premature or accidental death of just one person is quite costly to the economy to the tune of millions of dollars. Thus by saving more lives, sustainable economic growth is sustained.
It has also been revealed that a lot of time is spent at signalized intersections. This is because motorists have to wait for a long time in order to get their signal. In contrast, although roundabouts cause a slower flow of traffic, the fact still remains that traffic moves. This is even more advantageous because pedestrians are less susceptible to being knocked down by motorists. This adds to the list of benefits of roundabouts. To add on this, traffic volumes in roundabouts is greatly reduced. Thus there may be much traffic volume which is flowing. However, in signalized intersections, motorists may experience inconveniencies accompanied by increased volume of traffic.
As it has been discussed, major reforms are taking place throughout the world to ease traffic congestion. As a result many signalized intersections are being replaced by modern single lane roundabouts which are safer for both motorists and pedestrians.
Reference List
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CTC & Associates LLC, (2002). Roundabouts and Public Acceptance. Bureau of Highway Development, Division of Transportation Infrastructure Development.
Traffic Engineering Forum at Eng-Tips (2008). Web.
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Reid, M.(2010). Longboat Key News, Roundabouts earn Sarasota vote. Web.
Scares, R (2010). Circle of influence. How France has used roundabouts to cut casualties. International Road Assessment Program (iRAP), Case 5.
U.S. Department of Transportation, FHWA, (2010). Safety at Signalized Intersections. Web.
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