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Main Influences in Modelling and Simulation of Urban

Traffic Flows

JANOS TIMAR, DANIELA FLOREA, CORNELIU COFARU, DINU COVACIU

Faculty of Mechanics

Transilvania University of Brasov

B-dul Eroilor nr.29, Brasov

ROMANIA

jamcsika_timar@unitbv.ro http://www.unitbv.ro

Abstract: - Traffic modelling and simulation is an increasingly used and effective tool for analyzing a wide

variety of dynamical problems which are not suitable for study by other means.

This research paper presents a real application for the urban area, more precisely in Brasov city, where there

was noticed some problems in the urban traffic: congestions, conflict points. The data collected for one of the

busiest arterial streets of the city has represented the input data for the modelling and simulation program

Synchro plus Simtraffic 6. A new solution was proposed based on the analysis of the main influences of roadgeometry, signalisation and traffic conditions.

Key-Words: -Traffic simulation, traffic modelling, urban mobility, road safety, traffic flows, adjustment

factors.

1. IntroductionThe researches performed in a very congested area

of Brasov city, usually named the big roundabout,

permitted to identify the real problems generated by

the last solution for urban traffic management:

traffic jams, many conflict points between vehicles

and weaving of traffic flows. The map of area of

interest is shown in Fig.1.

Fig.1 The map of studied area

2. Data acquisitionAfter a general analysis of the area in order to

identify the actual situation, many activities were

organised to prepare, measure and analyse the

traffic flows.

Thus, arrival patterns, traffic volume distribution inthe entrance of each signalised or unsignalised

intersection were established. The variation of

traffic volumes for a representative period in a day

is presented in Fig.2.

Vehicle distribu tion per lane

acces from Toamnei street

0

50

100

150

200

250

300

lanes

numberofvehicule

9:00-9:15 9:15-9:30 9:30-9:45 9:45-10:00

Fig.2 Traffic volumes at Toamnei Street

2.1. Evaluation of the saturation flow rateCapacity analysis of the area can be made only after

the identification of the saturation degree of each

intersection.

The ideal saturation flow rate, S for the group of

lanes at the entry of a signalized intersection,

expressed in unitary vehicle per hour (Vt/h), is

influenced by the ideal saturation flow, S0, the

number of lanes N, and a very important number of

adjustment factors fi as in relation (1).

=

=11

1

0

i

ifNSS (1)

Computation is based on the ideal saturation flow

considered as 1900 Vt/h/lane. A realistic result of

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineering

ISSN: 1790-2769 213 ISBN: 978-960-474-119-9

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1800 Vt/h/lane is if someone consider the gap

between the following vehicles are 2 seconds.

Adjustment factors

The main influences of modelling contained by the

adjustment factors, are presented in the following

equations [3].

Lane width, W

9

)5.3(11

+=

Wf (2)

The value 3,5 represents the standard width of a

lane. The variation of the lane width from the

standard 3,5 m to 4,0 m produce a variation of the

adjustment factors f1 in the 1,0 1,06 limits

corresponding with the increase 5,6% of ideal

saturation flow rate S, expressed in unitary vehicle

Vt/h/lane (Table 1).Table 1

Lane width, m 4 3,9 3,8 3,7 3,6 3,5

f1 1,06 1,04 1,03 1,02 1,01 1

S, Vt/h 1900 1880 1860 1840 1820 1800

Reducing the lane width from 3,5 m to 2,5 m produce

a variation of the adjustment factors f1 in the 1,0

0,89 and as consequence reducing the traffic volume

to 11,1%, that means 1800 Vt/h/lane to 1800 Vt/h/lane

(Table 2).

Table 2Lane

width, m3,5 3,3 3,2 3,1 3 2,8 2,7 2,6 2,5

f1 1 0,98 0,97 0,96 0,94 0,92 0,91 0,9 0,89

S, Vt/h 1800 1760 1740 1720 1700 1660 1640 1620 1600

Heavy vehicles

)1(%100

1002

+=

TEHVf (3)

The percentage of heavy vehicles, %HV has an

important influence in traffic flows. This value is

between 0 30% and produce a variation of theadjustment factors f2 in the limits 0,77 1,00 and at

the same time a decrease of the ideal saturation flow

rate with 23% (table 3).

The formula considers also the coefficient ET to

transform the heavy vehicles in unitary equivalent

(passenger cars).

Table 3

Heavy traffic, % 0 4 8 10 20 30

f2 1 0,96 0,93 0,91 0,83 0,77

S, Vt/h 1800 1731 1667 1636 1500 1385

Grade

200

%13

Gf = (4)

If intersection is located in an area where the road is

tilted as a consequence this will generate to increase

traffic flow by 3% (when the grade %G on lane

group approach is -6%) and grade ranged from 0%to 10%, a decrease of 5%. The area studied is

located on the ground horizontally so there is no

influence.

Parking

N

NN

f

m

3600

181.0

4

= (5)

Locations of parking near signalized intersections

affect negatively the flow of saturation, especially in

the case of a single lane in the movement direction.The coefficient f4 varies in this case the value of

1.00 when there is no parking at the 0.7 to be carried

out when the number of parking Nm is 40 parking

manoeuvres per hour. In this case the reduction of

traffic is 30%.

Bus blockage

N

NN

f

B

3600

4.14

5

= (6)

Where:NB number of buses stopping/h within 75 m

upstream or downstream of the stop line, taking into

account when the stopping buses block traffic flow

in the considered lane group.

Lane utilization

)/( 16 Nvvf gg = (7)

Where:

Vg unadjusted demand flow rate for the lane

group, expressed in vehicles per hour.

Vg1 unadjusted demand flow rate on the single

lane group with the highest volume.

Left turns (LT)

The consideration of this factor takes into account

the two situations. For exclusive lane:

95.07 =f ,

and for shared lane:

LTPf

05.00.1

17

+= , (8)

where, PLT proportion of LTs in lane group.

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineering

ISSN: 1790-2769 214 ISBN: 978-960-474-119-9

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Right turns (RT)

For exclusive lane:

85.08 =f ,

for shared lane:

RTPf )15.0(18 = (9)and for single lane

RTPf )135.0(18 = . (10)

The main parameter is PRT, proportion of RTs in lane

group.

Pedestrian bicycle blockage

LT adjustment

)1)(1(0.19 LTApbTlT PAPf = (11)

RT adjustment

)1)(1(0.19 RTApbTRT PAPf = (12)

Where:

PLT and PRT proportion of LTs and RTs in lane

group,

ApbT permitted phase adjustment,

PLTA and PRTA proportion of LT, respectively RT

protected green over total LT green

3. Proposal for new solutionThe critical analyses of modelling and simulation

results permitted to formulate a new proposal.

With the proposed solution it modifies the sense of

change and movement of traffic, which runs one-

way only on a certain segment of the route, rest in

two-way

The traffic will be conducted by the proposed study

in two directions so the volume of traffic is higher

from the intersection M. Kogalniceanu - Bd

November 15 - I. Maniu intersection to Bd

November 15 Toamnei Street Zizinului Street

Calea Bucureti. With the implementation of this

solution, two factors have remained unresolved: thenoise and possible points of conflict pedestrian -

vehicle and vehicle-vehicle.

Fig.3 Real scheme of the route

Fig.4 Proposed scheme of the route

The intersection named B-dul Hrmanului Toamnei

Street B-dul M. Koglniceanu is an intersection

with three branches and two accesses (Toamnei

Street, and B-dul M. Koglniceanu).

The proposed intersection scheme will have an

actuated control type. This actuated control type

would require installation of inductive loops and

connecting them to a central unit. Another change is

that the intersection will have 3 accesses and on

Toamnei Street will come back in two-way traffic.

Benefits of the actuated control type:

9Increase the capacity of

movement

9Reduce delays

9Allows synchronization of the

signalized programs

Access to the intersection will be done according to

the request in this way advantaging the main traffic

flows.

In the study we had made one of the following

problems had been identified in the intersection:

9 queues that form on the Toamnei Street

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineering

ISSN: 1790-2769 215 ISBN: 978-960-474-119-9

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Fig.5 Queues in the simulation

software

Conflict points of vehicle-vehicle appeared in traffic

flows between the two accesses of the intersection (B-

dul Harmanului and Toamnei Street) as you can see in

Fig.6.

Fig.6 Vehicle-vehicle conflict at

Toamnei Street

Fig.7 Vehicle-pedestrian conflict at

Toamnei Street

3 SimulationIn the following are presented comparative graphs

between the actual situation and the proposed one:

speed of movement, fuel consumption, stops/vehicleand delays.

Fig.8 Speed of vehicles in real

situation

Fig.9 Speed of vehicles in proposed

situation

Fig.10 Fuel efficiency of vehicles in

real situation

Fig.11 Fuel efficiency in proposedsituation

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineering

ISSN: 1790-2769 216 ISBN: 978-960-474-119-9

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Fig.12 Stops of vehicles in real

situation

Fig.13 Stops of vehicles in

proposed situation

Stops occur in areas where traffic flows are

intersecting and traffic volumes are high. The

crossing of traffic flow generally occurs at the exit

or entry into intersection, when most drivers try to

get on a lane on which to continue their movement

towards the next intersection. Some vehicles will be

forced to stop in order to fit in lane that they wish to

continue their movement.

Fig.14 Delays of vehicles in real

situation

Fig.15 Delays of vehicles in

proposed situation

Delays are caused by conflicts of the pedestrian with

vehicles, arising in particular for vehicles that madea right turn onto B-dul Hrmanului from Toamnei

Street.

4. ConclusionsThus the proposed solution reflected the results

from the actual situation regarding: time delays

generated by the vehicle stops, fuel

consumption efficiency, the formation of

queues, reducing the conflict points. Even a

doubling of existing traffic volumes, has notcreated large queues.

References:[1] Florea D., Aplicaii telematice n sistemele

avansate de transport rutier, Editura UniversitiiTransilvania din Braov, ISBN 973-635-258-7,

2004

[2] Florea D., Cofaru C., Soica A.,Managementul

traficului rutier, Ediia a II-a, Editura Universitii

Transilvania din Braov, ISBN 973-9474-55-1,

2004

[3] Transportation Research Board (TRB), Highway

Capacity Manual 2000, Washington, DC , National

Research Council , 2000

[4] Federal Highway Administration, Signalized

intersections: Informational Guide, U.S. Department

of Transportation, 2004

[5] Trafficware Ltd., Synchro 6,

http://www.trafficware.com

[6] Trafficware Ltd., SimTraffic 6,

http://www.trafficware.com

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineering

ISSN: 1790-2769 217 ISBN: 978-960-474-119-9

http://www.trafficware.com/http://www.trafficware.com/http://www.trafficware.com/http://www.trafficware.com/