Roundabout Crri

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CAPACITY AND LEVEL OF SERVICE ANALYSIS OF

ROUNDABOUTS

M.V.L.R.AnjaneyuluProfessor, Department of Civil Engineering

National Institute of Technology Calicut – 673601, Kerala, [email protected]

Abstract: Roundabout is a form of at-grade intersection control, which accommodates

traffic flow in one direction around a central island. Roundabout is becoming more popular

due to its better operational and safety characteristics than rotaries and signals. Poor road

planning and sub-standard geometric conditions of roundabouts adversely affect the

roundabout capacity and thereby traffic flow. Therefore, it is essential to evaluate the

capacity and performance of roundabouts for proper traffic operation. The empirical,

analytical and simulation approaches used for modelling capacity and performance of

roundabouts are briefly discussed along with their merits and demerits, suitability for Indian

conditions and are compared on based on experimental studies.

1.0 INTRODUCTION

Road traffic congestion is a major challenge nowadays. The result of traffic

congestion is the urban streets with vehicle movements characterized by the slowness, delays

and increased fuel consumption. The rapidly growing vehicular traffic, limitations on the

construction of new infrastructure, hazardous environmental impact due to the emission of

pollutants, together with unfavourable delays suffered in congested traffic jams, are among

the basic features which necessitate the search for tools and techniques to improve the traffic

conditions by the best possible use of existing network of streets. Inevitably, this task would

not be significantly fulfilled unless a comprehensive study of different types of intersection

controls is carried out.

Intersection performance can be significantly improved by having a suitable

intersection control. Many types of traffic control are being used worldwide at intersections,

including yield sign, stop sign, rotary, and signal. Modern roundabouts have quite recently

come into play as alternatives to signalised intersections, which tend to control the traffic

flow more optimally and in a safer manner. A roundabout is a form of intersection control

which accommodates traffic flow in one direction around a central island, operating with

yield control at the entry points, and giving priority to vehicles within the roundabout

(circulating flow). The era of modern roundabouts began in the United Kingdom in the

1950’s with the construction of the first “yield-at-entry” roundabouts. The primary

characteristics of the modern roundabout such as, yield-at-entry, deflection of the vehicle

path and entry flare, distinguish the modern roundabout from the traffic circle, which does

not have these characteristics.

Due to many advantages, like higher capacity, high fluidity, higher safety, lesser

operating cost, lesser area requirement, less vehicle operating cost, improved aesthetics,

roundabouts have become popular and also a subject of greatest interest and attention over

the last few years throughout the world. Poor planning and sub-standard geometric conditions

of roundabouts have a significant effect on roundabout capacity and traffic congestion. It is

necessary for traffic engineers to have a methodology for estimating capacity and delay at



roundabouts for the purpose of operational, design, and planning analyses. A large number of

roundabout studies have been conducted around the world. However, little attention has been

given to roundabout studies in India. Hence, there is a need to conduct studies in order to

evolve guidelines. This paper presents briefly the various methods used for capacity and

performance analysis of roundabouts around the world and their suitability to Indianconditions based on experimental studies.

2.0 FEATURES OF ROUNDABOUT

A roundabout is a form of intersection design and control, which accommodates

traffic flow in one direction around a central island and gives priority to vehicles within the

roundabout (circulating flow). Roundabout is defined by following three basic operational

and design principles:

“Yield-at-entry” or “priority-from-right” rule - This rule requires that entering

vehicles yield to vehicles in the circulatory roadway. Vehicles in the circulatory

roadway have the priority of movement and all entering vehicles on the approacheshave to wait for a gap in the circulating flow.

Deflection on approaches - Deflection is the second design element that is unique to

roundabouts. Deflection is a design technique applied to the entries of roundabouts

that helps to smooth the transition between the straight approaches. No tangential

entries are permitted and no traffic stream gets a straight movement through the

intersection. The use of deflection in the design of roundabout helps to slow entering

vehicles and improves safety at merging points.

Flared Entries - The final design element that is sometimes applied to roundabouts

is flared entries. Flared entries are used to increase capacity of the entry by increasingthe number of lanes before the yield line, which accommodates more vehicles, there

by increasing the entry capacity.

2.1 Geometric Elements of Roundabout

Geometrics affect capacity and safety of a roundabout. The various geometric elements of a

roundabout are illustrated in Figure 1.

Fig. 1 Geometric Elements of Roundabout



3.0 OPERATIONAL PERFORMANCE OF ROUNDABOUTS

The prime indicators of the operational performance of a roundabout are the capacity

and delay. Roundabout capacity and performance characteristics are influenced by both

driver behaviour and intersection conditions such as intersection geometry and traffic control.

The important parameter that is influenced by the driver behaviour is the gap. A driverentering a roundabout has to make a decision whether there is sufficient gap to enter the

intersection safely. The drivers in the approaching stream assess the gaps on the conflicting

stream. They decide based on their perception, if the gap is too small to cross or large enough

to safely manoeuvre their vehicle. In the former case they would reject the gap and maintain

their current position and in the latter case they would accept the gap and merge into the

circulating stream.

The different approaches available for the operational analysis of roundabouts are the

empirical approach, the analytical (gap acceptance based) approach and the simulation

approach. The empirical approach does not account for the gap acceptance behaviour of thedriver which is the major setback of it. Empirical models require an extensive amount of data

with sufficient variation of each parameter. These models are based on statistical regression

and represent driver behaviour by the relationship between geometric elements and road

performances. These methods are easy for geometric design purpose.

Methods based on gap acceptance theory represent driver behaviour based on vehicle-

vehicle interaction. Calculation of capacity using these methods requires fewer amounts of

data. These methods are easy for planning purposes. These methods are based on the

assumption that no driver enters the intersection unless the gap in the circulating stream is at

least equal to the critical gap. Certain traffic conditions (e.g.; queues that buidl over both time

and space) and variation among drivers cannot easily be analyzed by analytical methods.

Simulation models are based on the microscopic approach in which the behaviour of

individual components of the system is considered. It is possible to include many influencing

factors and conduct experiments under controlled conditions. Further, they can be used to

simulate a wide range of conditions with relative ease and without the need to collect the

costly data. It is also possible to create combinations of road and traffic conditions that are

hardly observed but which are felt necessary to be simulated by researchers. Many simulation

tools like Simtraffic, Corsim, PARAMICS, and VISSIM are available for the traffic analysis.

4.0 CAPACITY ANALYSIS

The Highway Capacity Manual defines the capacity of a facility as “the maximum

hourly rate at which persons or vehicles can reasonably be expected to traverse a point or

uniform section of a lane or roadway during a given time period under prevailing roadway,

traffic and control conditions”. While capacity is a specific measure that can be defined and

estimated, level of service is a qualitative measure that characterizes operational conditions

within a traffic stream and their perception by motorists and passengers. Capacity of

roundabout is measured in terms of entry capacity. The yield-at-entry rule assigns priority to

circulating vehicles. Under this rule, the roundabout can be considered as a series of T-

junctions. The entry capacity is dependent on the conflicting circulating flow and the

geometric elements of roundabout. While the capacity models used in UK and Germany are



based on regression analysis, the models recommended in Australia, US and Germany are

based on gap acceptance theory.

4.1 Regression Analysis

The UK roundabout capacity formula is based on Kimber’s study2in 1980 and is:

Qe = A – B Qc

Where: Qe = Entry Capacity, vph

Qc = Circulating Flow, vph

A, B = Regression coefficients

Germany uses an approach similar to that of the UK. However, an exponential

regression model has been recommended to describe the entry/circulating flow relationship.

The formula used in Germany is:

/10000c DQ

eQ C e

Where: C, D = Regression coefficients

This empirical formulation has the following drawbacks:

The data have to be collected at saturated flow level and extensive amount of data

with sufficient variation in each parameter is required, which is a painstaking task.

It is very difficult to collect the significant amount of data to ensure reliability of

results.

This method is sometimes inflexible under extreme circumstances e.g. when the

value is far out of the range of regressed data.

Reliability of predicted values depends on the methods of sampling and sample size.

Some geometric parameters, which are in model may prove to be statistically

significant, but cannot be explained logically.

In spite of all above demerits, regression models are easy for geometric design

purposes. These models will imply the driver behavior by the relationship between geometric

elements and road performances.

4.2 Gap Acceptance Theory

Gap acceptance models have theoretical basis, which represent the driver behavior

based on vehicle interaction. An advantage of this method is that gap acceptance technique

offers a logical basis for the evaluation of capacity. Also, it is easy to appreciate the meaning

of the parameters used and to make adjustments for unusual conditions. The development of

gap acceptance based capacity formula was fundamentally based on Tanner’s capacity

equation for priority intersection. Gap acceptance theory relies on the size and distribution

(availability) of gaps in the major traffic stream and the usefulness of these gaps to minor

stream drivers. In the gap acceptance technique critical gap is the most influencing parameter.

Roundabout capacity models recommended by ARRB, HCM and Germany are based on gap

acceptance theory.

4.2.1 Australian Capacity Formula

Troutbeck has modified Tanner’s equation to account for the bunching of vehicles in

circulating stream. In this method, the bunching of vehicles in circulating stream is described by Cowan’s M3 headway distribution, which assumes that a proportion, α (free vehicles) of



the major stream vehicles are “non- bunched” and have an displaced exponential (shifted

exponential) headway distribution and the others have the same headway of (intra bunch

headway or headway between bunched vehicles). The probability density function for the

Cowan’s M3 headway distribution is represented as:

t;0

t;1

t;e

tf

t

Where = Decay constant calculated from the equation =q

q

1

The cumulative density function of Cowan’s M3 headway model is represented as:

t;0

t;e1)t(F

t

The formula for entry capacity is given by

o

c

e1

eQ)1(3600Q

)(

e

Where Qc = Circulating Flow rate, veh/sec

= Critical gap, sec; o = Follow-up time, sec

4.2.2 HCM Capacity Formula

Using gap acceptance theory, Kyte proposed capacity formula that is same as for Two

Way Stop Control intersection and is given in HCM4 as

3600 / Q

3600 / Qc

e0c

c

e1

eQQ

4.2.3 German Gap Acceptance Capacity Formula

Wu5 modified the Tanner’s equation and proposed the following formula for

estimating the capacity of an entry to a roundabout.

)t(Q

o

e

n

c

c

e

oc

c

e

n

n

Q

1Q

Where: to = τ– τ 0 /2.

nc = Number of circulating lanes; ne = Number of entry lanes

= Minimum headway between vehicles in the circulating flow, sec

Capacity models developed based on gap acceptance theory have following

advantages:

Under simplified assumption of gap acceptance theory, fewer amounts of data are

required.

Gap acceptance technique offers a logical basis for the evaluation of capacity and it is

easy to appreciate the meaning of the parameters used and to make adjustments forunusual conditions.



Gap acceptance theory conceptually relates traffic interactions at roundabouts with

the availability of gaps in the circulating traffic stream.

In spite of a number of advantages, the gap acceptance theory suffers from the

following limitations

Reliability of prediction depends on the developed model and its assumptions. When model gets complicated, method to obtain and verify data will also become

complicated.

5.0 PERFORMANCE ANALYSIS

Performance analysis is carried out to know the quality of service provided by a

facility. Three performance measures are typically used to estimate the performance of a

roundabout: degree of saturation, queue length, average queuing delay. Each measure

provides a unique perspective on the quality of service at which a roundabout will perform

under a given set of traffic and geometric conditions. Delay is generally used as a

performance measure of roundabouts. For modeling the delay at roundabout two formulae,

one given by Highway Capacity Manual and the other given by ARRB, are available.

5.1 HCM Delay Formula

Average delay per vehicle as given in HCM is

T450

xQ

3600

)1x()1x(T900Q

3600D

e2

e

where: D = Average delay, sec/veh; x = Degree of saturation

Qe = Entry Capacity. Vph; T = Analysis time period, hr.

5.2 Australian Delay Formula

Akcelik and Troutbeck gave the following formula for calculating average delay,

which was adopted in the Australian Design Guideline (AUSTROADS, 1993)6

T450

xD1x1x900DD min2

min

Where: Dmin = Adam’s delay given by

)(2

2212)(

min

T q

e

D c

The following sections summarise the procedure followed for data collection,

analysis, development of capacity models, performance analysis of roundabouts in three

different studies7, 8, 9

carried out National Institute of Technology Calicut. A total of seven

roundabouts, in two different cities of Kerala, were studied and the details of six roundabouts

are presented here.

6.0 DATA COLLECTION & ANALYSIS

Data collection and analysis plays an important role in studies of this nature. Data

required for the capacity and performance analysis of roundabouts includes the informationabout flow, headways in major stream (circulating flow), critical gap and follow-up time of



entry stream vehicles. Geometric details of the roundabouts were collected by organizing

plane table or total station survey and the base map of the roundabout, as shown in Figure 2,

was prepared. Geometric details of the approaches were tabulated as presented in Table 1.

Due to its many advantages video graphic technique was adopted for the collection of

the necessary traffic data. Video camera was positioned on the top of an adjacent tallstructure and was oriented in such a way that it covers each approach of the roundabout for

sufficient length. The video recording was carried out on a clear day and under dry pavement

conditions. The traffic flow was recorded during morning and evening peak periods. During

recording the built in timer of the video camera was switched on. The following procedure

was adopted for the retrieval of the data from videocassettes.

Fig 2 Geometric Details of R2 Junction

Table 1 Geometric Details of the Modelled Junctions

Geometric

Element

R1 R2 R3 R4

Approach Approach Approach Approach

1 2 3 1 2 3 4 1 2 3 4 1 2 3 4Approach width

(m)4.44 6.00 4.51 5.79 6.52 7.35 4.96 5.58 8.32 3.98 10.06 8.58 10.62 8.32 7.38

Entry Width (m) 4.86 6.46 5.10 6.14 7.12 7.95 5.32 5.96 8.66 4.23 10.45 8.84 10.92 8.63 7.62

Entry Angle 27.2 25.3 - 24.50 27.00 25.50 21.00 28.20 32.30 24.6 23.20 24.30 23.60 28.20 26.30

Entry Radius (m) 24.5 30.2 - 29.00 22.50 24.00 32.70 23.60 21.70 27.40 30.40 30.40 32.30 23.20 26.50

Inscribed Circle

Diameter (m)33.00 44.80 42.50 49.60



6.1 Traffic volume

Traffic volume data was retrieved from the recorded viedo with the help of the

programs written in C. As and when a vehicle passes the marking on the approach the

designated key depending on the type of vehicle was pressed. The program writes the vehicle

type and time of passage details to a file. This data was analyzed to get the classified volumecount for the selected time interval. For the both circulating flow and entry flow classified

traffic volume count were obtained.

6.2 Critical gap

Critical gap is defined as the minimum gap that all entering drivers will accept to

merge with the circulating flow, assuming that all entering drivers are consistent and

homogenous. In evaluating the critical gap it is apparent that a given gap must be either

accepted or rejected by a given driver. For finding out the critical gap Raff’s method was

used. Gap required for the first driver, who is present in the queue at the entry to merge with

the circulating flow was used for this purpose. As the critical gap varies depending on type of vehicle and entry angle, the critical gap values were estimated for each type of vehicle and

for each approach.

6.3 Follow-up time

Follow-up time for minor stream vehicles was found out as the headway between

vehicles utilizing the same gap in the circulating traffic flow. Headways were collected for

each type of vehicle with different types of front vehicles for minor stream flow and the

follow-up time for the aggregate data is also collected.

For follow-up time and critical gap, statistical test were conducted to check the

significance of the type of vehicle in front and the type of vehicle considered. It was found

that there is no influence of vehicle type on both follow-up time and critical gap. Hence the

weighted average, based on the composition of the stream, was taken for further analysis.

Values of critical gap and follow-up times for different approaches were tabulated as given in

Table 2

Table 2 Critical gap and Follow-up times

Parameter

R1 R2 R3 R4

Approach Approach Approach Approach

1 2 3 1 2 3 4 1 2 3 4 1 2 3 4

Critical Gap (sec) 2.33 2.21 2.42 2.28 2.30 2.22 2.36 2.40 2.35 2.34 2.25 2.41 2.39 2.47 2.51

Follow up time(sec)

1.41 1.72 1.77 1.76 1.71 1.72 1.75 1.74 1.74 1.75 1.76 1.83 1.77 1.75 1.74

6.4 Capacity data

2-minute counts of both circulating flow and entry flow were taken for all the

approaches simultaneously. This data includes classified volume count along with the

corresponding turning movement. This data was collected when saturation flow conditions

were present in all the approaches in that 2 minutes time. This data was used for the

calculation of the roundabout capacity.



6.5 Delay Data

During each 15-minutes of time period and when queue was present in entry stream,

individual delay to every vehicle in the queue was recorded. The average vehicle delay was

calculated. This average delay was used as observed delay in the performance analysis.

7.0 CAPACITY MODELS

Capacity models were developed using regression analysis, gap acceptance theory and

simulation approach.

6.1 Regression Analysis

Regression models were developed relating the entry flow and circulating flow under

saturation flow conditions. The values of regression parameters for linear and exponential

models are given in Table 3 along with R2

values. Validation of the models was carried out

by comparing the RMS values for the validation data set. It can be observed that the

performance of exponential model is better compared to linear model.

Table 3 Comparison of regression modelsApproach Linear regression model

(LRM)

Exponential regression model

(ERM)

RMSE

A B R2

C D R2

LRM ERM

R5-1 1533 0.451 0.576 1733 5.10 0.571 29.35 26.33

R5-2 2655 1.122 0.779 2032 7.21 0.766 34.75 37.98

R5-3 2010 0.212 0.674 2667 3.00 0.680 20.77 20.79

R5-4 756 0.211 0.450 898 6.00 0.441 70.18 34.13

R6-1 2075 0.8192 0.67 2236 6.36 0.822 29.12 26.71

R6-2 1772 0.699 0.831 1896 7.37 0.712 36.38 30.29

R6-3 2176 0.7976 0.754 2405 6.83 0.801 33.47 25.72

R6-4 1819 0.7953 0.684 1936 5.23 0.695 39.24 29.46

6.2 Models based on Gap Acceptance Theory

Capacity models were also developed based on gap acceptance theory for each of the

approaches and using the three model formulations. Figure 3 shows a sample plot of

comparison of three gap acceptance models of capacity. It can be observed that capacity

values estimated using Australian model are very closely matching the observed values.

RMSE values of gap acceptance based models are given in Table 4. It can be concluded thatamong the gap acceptance theory based models of roundabout capacity the Australian

capacity model is best suited for our conditions.

Table 4 Comparison of RMSE values of Gap Acceptance theory based Capacity Models

Approach Australian

Model

HCM

Model

German

Model

Approach Australian

Model

HCM

Model

German

Model

R5-1 22.32 60.84 19.43 R6-1 9.70 27.60 22.18

R5-2 15.30 47.46 13.92 R6-2 13.23 28.77 12.80

R5-3 26.49 33.67 16.54 R6-3 11.76 23.96 10.42

R5-4 25.65 268.82 236.08 R6-4 12.41 18.85 18.27



Figure 3 Comparison of Gap Acceptance Models of Capacity

From the RMS values given in the above tables it can be concluded that Australian

gap acceptance model shows better performance than regression models.

6.3 Simulation Models

The study roundabouts were modelled in VISSIM. VISSIM is a microscopic, time-

step and behaviour-based simulation model. In terms of operations, VISSIM is extremely

flexible. With VISSIM it is possible to model any kind of intersection (or sequence/network

of intersections). VISSIM features required for simulating roundabouts are link and

connectors, routing decisions, priority rules and reduced speed zones. Two of these features,

link-connectors and priority rules, are directly related to how vehicles enter/exit the

roundabout. Two others, routing decisions and reduced speed zones, simulate lane choice and

speed within the roundabout. By properly defining each of these features any roundabout can

be simulated. Figure 4 shows the screen shots of roundabouts modelled in VISSIM.

Figure 4 Screen shots of roundabouts modelled in VISSIM

The maximum number of vehicles that can enter from each of the approaches were

obtained at different circulating flows and these values were compared with the observed

values. Table 5 gives a comparison of RMSE values of gap acceptance based and simulation

models.



Table 5 Comparison of gap acceptance based and simulation capacity models

Model

R1 R2 R3 R4

Approach number Approach number Approach number Approach number

1 2 3 1 2 3 4 1 2 3 4 1 2 3 4

German 24.58 31.75 35.22 24.05 24.61 21.01 19.13 20.77 23.72 25.04 31.79 28.98 24.83 23.75 17.72

HCM 18.99 25.72 28.06 20.43 20.28 17.98 19.26 17.38 18.35 22.49 25.44 24.58 18 18.94 12.66

Australia 10.46 15.99 16.44 8.68 6.15 9.06 8.75 10.55 12.33 11.42 15.97 13.42 10.63 8.35 9.83

VISSIM 7.79 3.71 6.91 7.77 6.61 6.04 7.53 7.99 6.39 13.17 6.61 7.69 6.04 6.17 4.21

The simulation model is found to be better than Australian model. These models

predict capacities fairly well at moderate circulating flows. Models based on gap acceptance

theory were found to overestimate under low flow conditions and under estimate under high

flow conditions.

7.0 PERFORMANCE MODELS

The performance analysis of the roundabouts was carried out using the average delay

as performance measure. The average delay for each of the approaches was estimated using

both HCM, Australian formulae and using the simulation model. The average delay for

intersection was computed using the average delay and volume for each approach. Figure 5

shows the plot of observed delay and delay estimated using gap acceptance delay models and

simulation model for one junction. The RMSE values of different models are estimated and

presented in Table 5 for different junctions. A comparison of the % RMSE error values and

plots reveal that Australian delay model and simulation model are having good predictive

capability of which simulation model is the better one. Among the remaining Australian

delay model is better suited for Indian conditions.

Figure 5 Estimated Vs Observed Delay - R1

0

2

4

6

8

10

12

14

-1 4 9 14

E s t i m a t e d

d e l a y ( s e c )

Observed delay (sec)

OBSERVED

VISSIM

AUSTRALIA

HCM



Table 5 RMSE values of different models

Junction HCM Australia VISSIM

R1 3.55 2.45 1.46

R2 4.79 3.25 1.33R3 3.35 3.11 1.66

R4 6.77 3.55 1.28

8. SENSITIVITY ANALYSIS

The geometric elements like central island diameter, circulatory roadway width and

inscribed circle diameter can be varied, one at a time, for a selected intersection and the effect

on average delay can be studied. Similar experiments were carried out at one of the

intersections and Figure 6 shows the effect of central island diameter on average delay. Otherparameters, including inscribed circle diameter, are kept constant, which means as the central

island diameter is increased, the circulatory roadway width decreases. As the central island

diameter increases the average delay goes on decreasing up to certain extent and then again

starts increasing. So, the ideal range of central island diameter for the simulated roundabout

may be fixed as 10m to 15m.

8.0 CONCLUSIONS

A summary of the various approaches for modelling capacity and level of service of

roundabouts is presented along with their advantages and limitations. The results obtained

from three studies were compared to assess the suitability of each of these approaches for

Indian conditions. Exponential regression model was found to be better suited for our

conditions when compared to linear regression capacity model. Among gap acceptance

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25

A v e r a g e D e l a y (

s e c )

Central Island diameter (m)



models Australian gap acceptance capacity model is better suited to our conditions. The

predictive ability of the simulation model is better than other models.

For estimation of delay at a roundabout, the Australian delay model is better suited for

Indian conditions than the HCM model. Simulation model was found to estimate delay more

close to the observed values. Hence, it is recommended to adopt simulation approach fordeveloping standards or design guidelines, gap acceptance theory based models for

operational analysis and regression models for planning analysis.

References

1. FHWA, “Roundabouts: An Informational guide”, U. S. Department of Transportation,

Federal Highway Administration, publication No. FHWA-RD-00-067.Kimber, R.M.

(1980). The traffic capacity of roundabouts. TRRL Laboratory Report LR 942. Transport

and Road Research Laboratory, Crowthorne, England.

3. Troutbeck, R.J.(1998) “Background for HCM section on Analysis of Performance of Roundabouts”, Transportation Research Record 1646, Transportation Research Board,

National Research council, Washington, D.C, pp.54-62.

4. Transportation Research Board. (1994). Special Report 209: Highway Capacity Manual.

Transportation Research Board, National Research Council, Washington, D.C.

5. Wu, N. (1997) “Capacity of shared/short lanes at unsignalised intersections” In

Proc.,Third International Symposium on Intersections without Traffic Signals (M. Kyte,

ed.),Portland, Oregon, U.S.A., University of Idaho.

6. AUSTROADS (1993), Roundabouts, Guide to Traffic Engineering Practice, Part 6,

Association of Australian State Road and Transport Authorities, Sydney.

7. Sireesha B (2002), Capacity and Performance Analysis for Roundabouts, Unpublished

MTech thesis submitted to NIT Calicut

8. Raveendra P (2006), Modelling Of Capacity and Level Of Service for Roundabouts,

Simulation Modelling Of Traffic Roundabout, Unpublished MTech thesis submitted to

NIT Calicut

9. Caleb Ronald Munigety (2010), Simulation Modelling of Traffic Roundabout,

Unpublished MTech thesis submitted to NIT Calicut.

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Roundabout Crri