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Regarding the different tyoes of intersections available and its usage in an Indian scenario....

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Continuous Green-T Intersection Michael Josepha, Madhur Vyasb Department of Civil Engineering, Indian Institute of Technology-Bombay, Mumbai, India a Roll No.:120040097 b Roll No.:120040075

1. INTRODUCTION A T-intersection section is considered to be one of the trickiest intersections to design, especially when the flow of traffic is controlled by a traffic signal. As the primary road vehicles may not prefer the idea of stopping at the intersection for vehicles which are coming from the attached minor road. In this situation, the design of a Continuous Green-T intersection allows for free-flow operations in one direction on the primary direction and reduces the number of approach movements that are limited to three by using a free-flow right turn lane on the arterial and the corresponding cross street along with an acceleration/merge lane for the left turn movements from the cross street. This design is found mostly in the Unites States of America, the most prominent among them being Florida. In this report we have tried to design it for Indian conditions, with a primary focus on the urban T-Junctions. We have re-designed the free way, signals from a lefthand drive perspective. Also, we have included a short summary of the various research works going on for the Continuous Green-T intersection, highlighting their results and its consequences for our country.

2. CONTINUOUS GREEN-T INTERSECTION The intersection of a road with an already prevalent road, results in the formation of a three way junction. If the three arms of the junction are of equal size, we refer to them as a Y-junction and if one of the arms is a minor road, the resulting configuration is called a Tsection. A T-intersection can operate either through the use of signals or by relying upon the drivers to obey the right of way rules. A Continuous Green-T Intersection tries to optimize the traffic signals along with apt right of way, at the junction for minimal traffic congestion.

Joseph and Vyas

Figure: A sample T- intersection

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An experiment was done in Illinois, United States to allow going straight on red (like a right turn on red) when approaching a T junction on the main road, with the intersecting road on the left. It was a failure. This explains the separation of the leftmost road in a continuous green-T intersection.

In most designs, the main road includes two lanes on the side away from the intersecting road, the farthest (leftmost, in areas where traffic drives to the left) lane is given the right of way to proceed straight through the intersection at all times, denoted by a "green arrow". Continuous Green-T intersections have a left turn lane off the main road which is separated from traffic going straight. This allows for a traffic signal on only one side of the road. Apart from that, the design accounts for a much safer design, as the free left turning vehicles, don’t interrupt the flow of the vehicles primarily involved at the junction. They have a separate passage which is also at a much lesser angle of incidence with the main road.

Importance of Proper Design: The results of a study conducted by Main Roads, Western Australia, suggests that incorrectly designed seagull islands results in poorer traffic safety in such a way that the number of crashes taking place may increase along with the severity of the crashes i.e.; an increase in serious injury crashes. The findings of the study supports well designed installations of the Continuous Green-T, if the treatment is chosen for a particular site in preference to other types of treatments that may improve traffic safety. According to the report, improperly designed intersections/ could possibly result in the benefit/cost ratio less than one.

3. DESIGN DETAILS FOR LEFT-HAND SIDE DRIVING (With reference to Auto-CAD drawing) The design is in accordance to IRC-86-1983: Old Mumbai Highway-Road 1(primary road) is an arterial road Nanal Nagar Road-Road 2 is a sub arterial road Road 1 Design speed 80 Km/hr (table 1 IRC-86-1983) Carriageway width: 7.5 m (table 5 IRC-86-1983) Road 2 Design speed 60 Km/hr (table 1 IRC-86-1983) Carriageway width: 7m (table 5 IRC-86-1983) Camber to be provided is 2 %.

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Stopping sight distance(v=80 km/hr)=120m Stopping sight distance(v=60 Km/hr)=80 m Horizontal alignmentSuper-elevation 4 % (‘on urban section with frequent intersection it will be desirable to have e=0.04’) Max friction value 0.15 Min radius of horizontal curve(R ruling):265m (table 10 IRC-86-1983) Let assume radius of curvature 300 m Max f value(assuming e=4 %)=0.128 300m) Vertical minimum gradient 0.2% (for drainage purpose) To convert the given road from Right Hand Drive to Left hand Drive we will be taking a mirror image. This has been shown in the Auto CAD drawing. 4. TRAFFIC OPERATIONS FOR LEFT-HAND SIDE DRIVING (With reference to Auto-CAD drawing) The Continuous Green T-intersection is designed in such a way that one of the sides of the primary road i.e. Road-1 will have a free and continuous flow without the interruption of any traffic signal. It has been separated using the risen barrier-1. At the core of the intersection, only three movements would require signal assistance. This method of dividing various lanes according to the final destination makes this system extremely efficient as well as simple to follow. Among the three movements, the road 1 movement is of prime importance and suitable care is taken while defining the timings of the signals. Green T-intersections are not suitable for pedestrian crossings as the walking people will have to cross at least two lanes of moving traffic which never stops for any traffic signal. Hence, importance needs to be given for their easy travel, based on the situation, for example, if required sufficient amount of funds should be allocated towards construction of skywalk as per circumstances, especially in Indian conditions. 5. LOCATIONS IN INDIA The location we have chosen is a T- intersection in Hyderabad at Tolichowki where Nanal Nagar Road (Collector Street) meets Old Mumbai Highway (National Highway). The location has been presented in references. Currently we have a circle placed at the intersection, which at present causes a lot of traffic congestion. We have designed our continuous green Tintersection at this specific location. One of the primary reasons behind this selection was that, as of now there isn’t any pedestrian crossing at this area and the whole reason for congestion is the heavy traffic flow in the Old Mumbai Highway. This can be ably conquered by this intersection design.

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6. STUDIES and RESEARCH Title:Intersection Safety Case Study Author:US Depatment of Trasportation Year of Publication:Feb 2010 Publication details: Published by Federal Highway Administration Summary: This case study mainly concentrates on the successfully implemented continuous green T intesections. This answers following question: How can crashes and injuries can be reduced at T intersections and how effective it would be and issues it will face. In this study two rural T intersections are examined where continuous Green T intersection has been done. The results of these two implementations were as follow: 1.US-50 and SH 141, Grand Junction, CO :After the implementation of Conitinuous Green T intersection here, it experienced 100 percent decrease in angle crashes(from 16 to 0), 83.3 percent decrease in injury crashes(12 to 2), 56.3 percent decrease in total no of crashes(from 16 to 7). So this is a successful implementation of continuous Green T intersection. 2.US-160 and US-550, Durango, CO2 :fter the implementation of Conitinuous Green T intersection here, it experienced 100 percent decrease in angle crashes(from 16 to 0), 83.3 percent decrease in injury crashes(12 to 2), 56.3 percent decrease in total no of crashes (from 16 to 7). So this is a successful implementation of continuous Green T intersection. Figure in the right side shows the implementation of Continuous Green T intersection here. The overall result of the case study states that reduction in angle crashes at treated intersection is 96.8 percent, in injury crashes is 70 percent and in total crashes is 60 percent Title: Evaluation of Continuous Green T-Intersections on Isolated Under-Saturated Four-Lane Highways Author:Stephen Litsas and Hesham Rakha Year of Publication:July, 2012 Publication details: A paper prepared for the Transportation Research Board 2013 Annual Meeting Summary : According to this paper there are two types of continuous green T intersections one is traditional CGT and another is merging CGT. In the traditional CGT some lanes in continuous direction are kept with signals while others are free to pass without any stopping. In the lanes with signals vehicles have to stop to allow right turners from side street so that they can come on lanes directly when when turning onto the main thoroughfare, whereas for vehicles on the other lanes in the same direction, they need not to be stopped and are allowed to conitnuously passing the intersection On the other hand, merging CGT all lanes are allowed in the continuous direction to bypass the signal, and the right-turners coming from the side street have to merge onto the mainthoroughfare, the way in which a vehicle would merge onto a highway. t the CGT's provide equivalent efficiency , but in case of merging CGT confusion is much lesser which leads to greater safety. The main purpose of this research paper is to compare merging CGT with the standard intersection in terms of cost of implementation, benefits and impacts on enviroment. The modeling software, INTEGRATION, is used for computing the differences between both designs depending on these six categories : total delay, fuel consumption, hydrocarbon (HC), carbon monoxide (CO), Oxides of Nitrogen 135 (NOx), and carbon dioxide (CO2) emissions. In this research focus was not on comparison between safety provided by both the designs.

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For the software some variables and some constants are defined. Variables are as follows: 1. Volume/Saturation for main thoroughfare approching lanes upstream the intersection. 2. Volume/Saturation for side-stream approaching lanes upstream the intersection. 3. Percentage of turners(thru) is total percentage of vehicles turning from main thoroughfare to the side street. 4. Percentage of right turners: The total pecentage of vehicles coming from side street to the main thoroughfare and turning to right. This will also give percentage left turners. 5. Speed Limit : It is the speed limit of main thoroughfare and side street. It's unit is mph. Constants that are used are as follow: • A saturation flow rate is constant at 1800 veh/h/lane. • The main-thoroughfare is a four-lane road. • The side-street is a two-lane road, having one lane for each direction. • All the distances between starting and destination of vehicles were exactly 2 km away from the intersection, so every vehicle has to cover 4km. • Signal timings are optimized for every case. After running the simulation on INTEGRATION software the following results were produced: Graphs and tables related to the result are given on last page. Title: Safety Analysis of Continuous Green Through Lane Intersections Author: Thobias Sando, Deo Chimba, Valerian Kwigizile and Holly Walker Year of Publication: 2011 Publication details: Journal of the Transportation Research Forum, Vol. 50, No. 1 (Spring 2011) The pupose of this paper was to examine the safety of CGT intersections using the paired-i test and ordered probit statical models. The data for tests are taken from 9 CGTs in the city of jacksonville. As the result of this study the crashes were divided in 12 patterns as shown in the table at the last. Based on the proportions analysis, all the crashes were divided in three broad types: 1. Sideswipe crashes due to motorists weaving from adjacent through lanes so that they dont have to stop at red signal 2. Angle crashes due to motorists taking a left turn from a minor street and swerving into the CGT completely neglecting the “do not change lane ” warning. 3. Rear-end crashes due to motorists who unexpectedly come to halt on the CGT. Using the propotional analysis it is found that on average sideswipe crashes make the 6.01%. Also, on average, 4.68% vehicles turning left from the minor direction (conflict pattern five) crossing to the CGT make a total of 4.68% of all the crashes.

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References:

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Continuous Green-T Intersection

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