1 Prof. Marian Tracz, Prof. Janusz Chodur

ROUNDABOUTS WITH TRAFFIC SIGNALS

Krakow University of Technology Krakow, Poland Email: [email protected]

2 Prof. Marian Tracz, Prof. Janusz Chodur

Abstract Roundabouts with traffic signals are used in urban arterials on crossings with large traffic volumes and large left-turning movements. At total traffic volumes over 4000 veh/h a two-lane roundabout without traffic signals does not operate well. In order to increase the capacity traffic signals can be used with special adjustment of intersection geometry – using internal storage areas for left-turning movements. The paper presents designs of various layouts of roundabouts with traffic signals, describing also their advantage and drawbacks. The authors analyze signal settings with alternative phasing used at intersections that can provide the intersection capacity of about 6500 veh/h in 2x2 lanes arterials or even 8000 veh/h in 2x3 lanes arterials including leftturning movements of 600 veh/h. Key words: signalized roundabout, capacity, traffic performance

3 Prof. Marian Tracz, Prof. Janusz Chodur

INTRODUCTION Roundabouts with traffic signals are fairly common in urban and suburban areas of Polish cities, particularly the so-called “intersections with a central island”. One characteristic feature of their geometry is a tangential entry design, i.e. the axis of each entry and exit are tangential to the axis of the circulatory roadway around the central island. Such roundabouts are characterized by crossing maneuvers instead of merging, diverging and weaving maneuvers – typical of classic large roundabouts. The main feature of the analyzed roundabouts is that they work with twophase traffic signals (Fig. 1). The left turning capacity is determined by storage areas around the central island. In their design there is a close link between the geometry of the roundabout, traffic control and signal settings parameters. One frequent design and operational problem of such roundabouts with two-phase signal settings involves a collision between the needs of pedestrian movement and the capacity of left-turn movement. In optimization of the central island diameter, a probabilistic description of vehicle cyclic arrivals cycles is used. In the paper, a diagram helping to select the central island diameter and/or cycle length at known or predicted left-turning traffic flows is presented. In order to eliminate overloading of the internal storage spaces of the existing roundabouts with traffic signals, a new multiphase traffic signal control system has been installed. The paper presents a comparison of the efficiency of two- and multiphase traffic signal settings with the operation of channelized intersections with multi-phase traffic signals. The operation of signalized roundabouts was also compared with the operation of classic two-lane roundabouts with no traffic signals. Accident statistics indicate that roundabouts with traffic signals do not rank amongst the safest in Krakow. One such intersection, accommodating noticeable public transport (buses and trams) flows was rebuilt into the so-called turbine-roundabout to enhance its traffic road safety and performance. The paper presents the results of the reconstruction. CHARACTERISTICS OF ROUNDABOUTS WITH TRAFFIC SIGNALS The geometric scheme of a roundabout with traffic signals (SR) is presented in Fig 1.

4 Prof. Marian Tracz, Prof. Janusz Chodur

400 Pds/h

160 480 320

3 2

1 3,5 3, 5 3,5

180 400 270

veh/h phv= 0,17

A phv= 0,17 veh/h

600 Pds/h 2 R1

2 R1

4 5 6

R1 2

2 R1

A'

RH

30,0

C'

R1 2

R1 2

B

RL

3,5 3,5 3,5

10 12 11

D

3,5 3,5 3,5

B'

21,0

D'

27,0

R

12

Scheme of phases

R1 2

Phase I

Phase II

7 8 9

3,5 3,5 3,5

C

210 450 210

400 Pds/h

phv= 0,17 veh/h

600 Pds/h 300 585 175

veh/h pvh= 0,17

Pedestrians Vehicles

FIGURE 1 Scheme of a roundabout with traffic signals. A roundabout with traffic signals has channelized entries and internal storage areas (accumulation bays) where vehicles turning left wait for their green light, which allows their non-conflict operation. Usually the internal storage areas can provide capacity of left-turning movement from 250 to 600 pcu/h depending on the signal cycle length and size of this area, which depends on the central island diameter and the number of traffic lanes within the area. Roundabouts with traffic signals can reach very high total capacity by increasing the number of lanes at entries and within intersection. Beside high capacity, including high capacity of left-turning movement, the described roundabout also offers high performance in terms of delay at operation with simple two-phase traffic signals, and also at different phasing. However, it requires a large area. According to the Polish guidelines [Tracz, M. Chodur J, et al., 2001]:  the central island can be oval in shape determined by horizontal curves of intersecting one-way roadways and by curves for left-turning movement, or the shape of a circle (Fig. 1). The diameter of the central island in the range of 30-50 m is recommended,  it is recommended that the diameter of the curve on a single-directional road passing through the intersection should be selected so as to ensure that the tangential does not extend behind the stop lines on the entries to the intersection. It is recommended that the radius should range within RH = 150  300 m. Turning radius RL for left-turn movement should not be less than 10 m,

5 Prof. Marian Tracz, Prof. Janusz Chodur

 it is recommended to use separate lanes for left and – where necessary – right turning movements – depending on traffic flow demands. The number of straight-through lanes should be the same as on the street sections before intersection and behind it,  the number of lanes on the storage area on extension of a given primary entry should be equal to the number of through- and left-turning lanes,  if a tram line goes through the central island, the island diameter should allow for its stop on the island without it blocking the traffic from the storage areas. SELECTED PROBLEMS OF SIGNALIZED ROUNDABOUTS DESIGN In selecting the geometrical parameters of signalized roundabouts the same criteria are taken into consideration as for other at-grade intersections, i.e.: traffic safety, traffic performance, adjustment to the needs of vulnerable road users, minimization of environmental impacts and economy. Traffic performance of signalized roundabouts is attained when adequate capacity is ensured, and when there is no overloading of storage areas for pedestrian and vehicular road users and under conditions of required LOS. Accommodation of the requirements of pedestrian and cycle traffic demands means in practice providing convenient conditions for crossing the street and shortening the waiting time for the green signal. Designing the geometry and signal settings at an intersection should be conducted and optimized simultaneously. What is important in ensuring the efficiency of the roundabout with traffic signals is the storage areas dedicated to left-turning movements. One natural issue that emerges in the course of designing the central island diameter involves a conflict between the demands of vehicular and pedestrian traffic flows. Increasing the distances which pedestrians have to cross when the entries are widened, requires long cycle time, whereas the capacity of left-turning movement depends on the product of the number of cycles per hour and the number of places for vehicles in the storage area. Consequently, pedestrians are frequently required to walk in two stages, which results in shorter cycle time. In the analysis of the volume of the left-turning traffic flow, a probable number of vehicles gathering in the storage area within one phase can be calculated. This number of vehicles should not exceed the storage capacity of the area, which can be described by the following inequality:

Fa  N max

(1)

where:

Fa  storage areas on straight lanes within the internal storage area [E], Fa  l  length of the storage area [m], L  average length of the post for one vehicle [m], n p  number of lanes,

l  np , L

N max  probable maximum number of vehicles gathering within the storage area [E], determined Q T on the basis of their average number N śr  L , under the assumption of Poisson distribution 3600 of arrivals and at 95% probability, QL – traffic volume of left-turning movement (pcu/h), T – cycle length (s).

6 Prof. Marian Tracz, Prof. Janusz Chodur

After transformation of the inequality (1), the relationship between the length of storage area l and the maximum number of vehicles gathering within the storage area N max can be obtained:

N max  L (2) np On the basis of the above assumption, and further assuming that the storage area length lies within the range of the central island diameter (0,9÷1,0), and that it depends on the location of the signaling post, a diagram was developed to facilitate the selection of central island diameter or the signal cycle length (Fig. 2). Figure 2 also presents a method for determination of these two parameters. For example, for the assumed traffic volume of left-turning movement Q L = 400 veh/h at the signal cycle length T = 80 s, the diameter of the central island at np = 2 should be a minimum D = 47 m. Similarly, with the diameter of the central island D = 40 m and np = 3, the required signal cycle length can be determined to be T ≈ 86 s, which guarantees that the internal storage area is not overloaded at the assumed traffic volume of the left-turning movement Q L = 500 veh/h. l

Nśr [-] T=

0 12 T= 0 10 =? 0 T =8 T

18 17 16 15 14 13 12 11 10 9 8

T = 86 s

T=

60

7

6 5 4 3

2 1 600 500 400 300 200 100 5 10 15 20 25 30 D 9 0, 35 = a l 40 45 50 55 60 65 70 75 50 45 40 35 30 [m]

2

4

6

8 10 12 14 16 18 20 22 24

Nmax[E]

la =

D

QL [P/h]

D [m]

D = 47 m

n p =3

n p =2

la

FIGURE 2 Diagram for selection of central island diameter

7 Prof. Marian Tracz, Prof. Janusz Chodur

USE OF INTERNAL STORAGE AREA The practical size of the internal storage area (bays) is often larger than calculated on the basis of the number of marked lanes. It is a result of larger widths of lanes within these areas (due to widening). These lanes are widened to meet the driveability of long vehicles on curves. Monitoring of traffic on the signalized roundabouts investigated showed that on lanes wider than 4,5 m, cars often form two lines on one lane (Fig. 3). Another observation is related to an articulated bus, which in traffic flow calculations is equivalent to 3 pcu’s, whereas in such a line it uses the space needed by almost six cars.

FIGURE 3 Double line of cars on one lane in storage area

FIGURE 4. Overloading of storage area

Negative effects of the formation of two lines of cars on wide straight-through lanes within the storage area involve mutual conflicts of these cars at exits when departing from such an intersection. The process of regrouping of vehicles from three into two platoons also causes some delays and some decrease in entry capacity. If observations confirm that such situations are frequent, in the calculations of storage area capacity the number of platoons should be taken into account instead of the number of lanes. Internal storage spaces become overloaded in situations when the number of left-turning vehicles in a given phase using this area exceeds its capacity (Fig.4). The yellow color indicates the vehicles in the storage space. The green color denotes the vehicles that entered the intersection area when the green signal was on and there was no room for them within the storage area, but they were situated in front of the yield line of the storage area on the extension of the east entry. These vehicles, after getting the green signal in the next phase, will also leave the intersection, rather not interrupting the movement of the straight-through vehicles in this phase. The red color shows the left-turning vehicles which, after entering the intersection, were not able to pass the yield line of the internal entry due to overfilling of the storage space by left-turning vehicles which had earlier passed this line. So these vehicles can leave the intersection only in the next cycle, thus suffering additional delay.

8 Prof. Marian Tracz, Prof. Janusz Chodur

ANALYSIS OF OPERATIONAL PERFORMANCE OF TWO-PHASE AND MULTIPHASE TRAFFIC SIGNALING

Ma rsz ałk ow s

ka str.

The roundabouts with traffic signals installed at the beginning of their operation were designed to work in situations of two-phase traffic signal settings. Increasing traffic flow volumes in urban areas resulted in situations when this simple two-phase operation did not guarantee good performance of such roundabout operation. Usually the problems began with overloading of the internal storage areas by left-turning vehicles. Hence the demand for multiphase traffic signal settings that can limit the signalized roundabout blocking from the internal storage areas. Below the results of a comparative analysis of a signalized roundabout operating with two-phase and multiphase traffic signal settings, real and modeled intersections, are presented. In this analysis, the Polish capacity calculation method has been used [Chodur J. et al., 2004]. The layout of the signalized roundabout (located in the city of Rzeszow) is shown in Fig. 5. The traffic volumes in morning and afternoon peaks are shown in Fig. 6. The traffic signal phasing and the program of two-phase signal settings are presented in Figs 7 and 8. In such designs the internal storage areas were often overloaded. Therefore multiphase signal control systems presented in Figs 9 and 10 were suggested. In these analyses of performance the classic two-lane roundabout (without traffic signals) with the inscribed circle diameter equal to diameters of signalized roundabouts (case III) was also included. In this example the by-passes for right-turning were provided. In the analysis of the capacity and traffic performance of a roundabout without traffic signals, a method developed by the authors (recommended by the Polish General Directorate of National Roads) was used. It is based on the results of empirical measurements described in [Chodur J., 2005, Tracz M., Chodur J., 2006, Chodur J., Tracz M., 2008 ]

Pił

A

su d

sk i

B'

str .

C' D'

B

Pił su

dsk

i st r.

Cie pliń

ski

str.

A'

Legend A,B,C,D,A',B',C',D'- Entries - Traffic lanes - Signal heads for vehicles

D

- Signal heads for pedestrian

FIGURE 5 Geometrical layout of the intersection in the city of Rzeszow.

9 Prof. Marian Tracz, Prof. Janusz Chodur Afternoon peak Marszałkowska str.

1066 430

313 1270

313 840 202

1470 pc/h

125 812

5141pc/h

125 499 391

1470 pc/h

Piłsudski str.

412 681 377

806 377

Piłsudski str.

183 688 430

1301 pc/h

1015 pc/h Ciepliński str.

FIGURE 6 Design traffic volumes for signalized roundabout as in Fig. 5

Phase I

Phase II

C

1

C 13

12

6 9

A

A

2

B

4 11

14 5

B

7

16

8

10 15

3

D

D

FIGURE 7 Signal phasing at signalized roundabout as in Fig 5. T=70s Signals group number vehicles

Signal heads

2

1

26 29

70

K1, K1p1, K1p2

24 31 34

K11, K11p1, K11p2

33

2 2

3

66 68 70

26 29

70

K3, K3p1, K3p2

24 31 34

4

66 68 70

K31, K31p1, K31p2

33 34 36

62

65

K2, K2p1, K2p2

26

5 29 31

67

70

K21, K21p1, K21p2

36

6 34 36

62

65

70

K4, K4p1, K4p2

26

7 30 32

8

70

67

35

70

K41, K41p1, K41p2

FIGURE 8 Fixed time signal settings at the intersection presented in Fig. 5. (pedestrian signal groups were ignored)

10 Prof. Marian Tracz, Prof. Janusz Chodur Phase I

Phase II

C

1

Phase III

C

1

C 13

12

6

14 9

A

2

B

11

9

A

2 4 11

9

A B

4 11

B

16

8 3

D

3

D

Phase IV

D

Phase V

C

Phase VI

C

13

C

13

13

6

6 9

A

A B

7

6

5

B

7

8

A

5

2

B

11

8 10 15

15

D

15

D

D

FIGURE 9 Proposed phasing at the intersection presented in Fig. 5 TABLE 1 Comparison of traffic performance measures for the intersection presented in Fig. 5 with 2- and 6-phasing and at unsignalized two-lane roundabout Capacity and performance measures Intersection capacity [veh/h] Critical flow rate to capacity ratio q/C [-] Average overall intersection delay [s/veh]

I

Case II

Absolute difference

Relative difference

signalized (2-phase control)

signalized (6- phase control)

unsignalized Rbt)

II to I

III to I

II to I

III to I

6628

5230

4022

-1398

-2606

21%

39%

0,78

0,98

1,28

0,20

0,50

26%

64%

29

113

692

84

663

290%

2286%

III

On the basis of calculation results of capacity and traffic performance measures, it can be stated that after implementation of multiphase control, the performance of the intersection declined as:  in the case of a 2-phase control, the total intersection capacity is 20% higher if the internal storage areas are not overloaded,  the use of a 6-phase control in comparison with a 2-phase control V/C rates can increase at primary entries even by 27%, and also the vehicular delay can considerably increase,  2-phase control does not comply with the requirement of not overloading the internal storage areas by left-turning vehicles due to excessively long signal cycle and/or limited internal storage areas,  6-phase control can cause worse traffic performance in both traffic peaks, but can eliminate overloading of the internal storage areas. Two-lane roundabout at the analyzed traffic demands does not guarantee the required capacity and can generate very large delays. Further analyses for the modeled layout presented in Fig.10 gave results presented in Table 2. These results gave the basis for the following conclusions:  the use of a 2-phase traffic signal control can guarantee the highest intersection capacity on condition that risk of overloading of the internal storage areas is very low,  the use of 2-phase traffic signal settings with a sub-phase can provide efficient operation of the intersection without the risk of overloading of the left turns from entry A limited by

11 Prof. Marian Tracz, Prof. Janusz Chodur

the size of the storage area (entry D). However, this design decreases the total capacity of the intersection by 20%, causing an increase of average delay by about 50%,  the performance of an intersection with a 3-phase control is the lowest. With this control, the total intersection capacity drops by 33% and average delays increase nearly two-fold,  at analogic traffic volumes, an unsignalized two-lane roundabout does not guarantee the required total capacity even after building by-passes for large right-turning movements. The comparisons show much higher capacities of the signalized roundabout in comparison with a two-lane roundabout without traffic signals.

C 3,5 3,5 3,5 3,5 K3p1

K31p1

B

K41p1

C'

D'

42 R1 2

K21p1

K21

1000 370

K11p1

K1p1 K21p1

K1p2

A'

P1a

P3c

K11p2

P3d K4p2

P4d

P4b

K11

K1

5000 veh/h

R1

0

P4a

R1

2

P4c

K4p1

3,5

A

3,5 3,5

D

600 1170

600 800 200

A,B,C,D,A',B',C',D'- Entries - Traffic lanes

1040 veh/h

- Signal heads for vehicles

D

K1

- Signal heads for pedestrian P3a

Phase Ia

GP13

GP14

B GK4

B

C

GP11

GP13

B

GP14

GK3

GP13

GK4

GK3

GK4

Phase II

C

C GP11

GP11

GP10

Phase I

Phase Ib

C GP13

GK4

Phase II GK5 GP14

GK3

Phase I GP13

GK4

Legend

1600 veh/h

K4

350 500 190

3,5 3,5 3,5 3,5

P1b

240 500 400

850 400

K41

2

B GK8

GK8

GK2

GK6

A GP16

GP15

GP12

GP9

A

GP16

GP16

GP15

D

GK2

GK1

GK2

GK1

GK2

GK1

GK2

GK6

GK1

A

3,5 3,5 3,5

K3p2

K31p2

P3b

250 600 370

K2p2 K41p2

R1

B

K3

K31

P2b

P2d

K2p1

B'

P1c

1120 veh/h

C 1220 veh/h

P3a

P1d

350 1100

0

P2c

P2a

R1 2

K2

R1

GP15

A

GP16

GP15

D

GP9

GP15

D

GK7

Phase III

Phase II C

GK5

GK5 GP11

B

GP10

GP11

GP10

GK8

GK8

GK6

GK6

A GP9

GP12

2 phases signals

T = 49 s

GP12

GP9 GK7

D

GK7

2 phases signals with sub phase

3 phases signals

T = 60 s

T = 75 s

FIGURE 10 Layout, traffic volumes and signal phasing of the analyzed intersection.

12 Prof. Marian Tracz, Prof. Janusz Chodur

TABLE 2. Comparison of traffic performance measures for intersection presented in Fig. 10 with various traffic control methods Capacity and other measures of performance Intersection capacity [veh/h] Critical flow rate to capacity ratio V/C [-] Average overall intersection delay [s/veh]

Case III

I

II

IV

V

signalized (2 phases)

signalized (2+sub phases)

signalized (3 phases)

unsignalized (roundabout)

unsignalized (roundabout with bypasses)

8695

6985

5782

3709

4136

0,58

0,72

0,86

1,34

1,25

10,4

15,5

29,8

982

436

The larger the number of signal phases in the signal cycle, the longer the cycle time T and lower rate of effective green in cycle Ge/T. The impact of these parameters on delay in the analyzed group of lanes at an intersection entry of the roundabout with traffic signals is shown in Fig.11. The vehicular delays were analyzed in relation to Q/V function, where Q is traffic volume and C capacity of the group of lanes. The relationship presented in Fig.11 refers to the period of analysis equal ta = 1 h and initial saturation flow S = 1800 pcu/h. 100 90

s = 0,5 pcu/s t a = 1h

Average delay d [s]

80

G e /T = 0,3: T = 120 s T = 90 s T = 60 s

70 60 50 40 30

Ge/T= 0,7: T = 120 s T = 90 s T = 60 s

20 10 0 0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

1,1

Q/C Ratio [-]

FIGURE 11 Impact of Q/C and parameters of traffic signals T and Ge/T on average delay in the analyzed lane group. As the graphs in Fig.11 show, both lengthening of cycle time T and decreasing of effective green in cycle time Ge/T result in an increase of vehicular delay d. The addition of further signal phases often causes a significant increase of T and decrease of Ge/T, which leads to a significant increase of delay and worsening of performance of a roundabout with traffic signals. Therefore it is reasonable to search for such geometric design of intersection and traffic control, that allow the use of signal settings with the minimum number of phases (with regard to capacity, two-phase signal settings are the most efficient).

13 Prof. Marian Tracz, Prof. Janusz Chodur

TRAFFIC SAFETY AT SIGNALIZED ROUNDABOUTS Figures 12 and 13 show the statistics of road collisions and accidents at roundabouts with traffic signals in Krakow in the period of 2000-2010. Intersections:

160

Andersa - Bieoczycka Grzegórzecka - Powst. Warszawskiego

Number of accidents and collisions

140

Mikołajczyka - Broniewskiego Jana Pawła II - Bieoczycka

120

Pokoju - Nowohucka Konopnickiej - Monte Cassino

100

Pilotów - Młyoska Lublaoska - Bora Komorowskiego

80

Armii Krajowej - Conrada Kamieoskiego - Kalwaryjska

60

Dobrego Pasterza - Lublaoska trend Andersa - Bieoczycka

40

Grzegórzecka - Powst. Warszawskiego Mikołajczyka - Broniewskiego

20

Jana Pawła II - Bieoczycka Pokoju - Nowohucka

0 2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Konopnickiej - Monte Cassino Pilotów - Młyoska

Year

FIGURE 12 Annual numbers of accidents and collisions at signalized roundabouts in Krakow in the period of 2000-2010 25

Intersections:

20

Number of injured

Andersa - Bieoczycka Grzegórzecka - Powst. Warszawskiego Mikołajczyka - Broniewskiego

15

Jana Pawła II - Bieoczycka

Pokoju - Nowohucka Konopnickiej - Monte Cassino Pilotów - Młyoska

10

Lublaoska - Bora Komorowskiego Armii Krajowej - Conrada Kamieoskiego - Kalwaryjska 5

Dobrego Pasterza - Lublaoska Log. (trend)

0 2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Year

FIGURE 13 Annual numbers of injured at signalized roundabouts in Krakow in the period of 2000-2010

14 Prof. Marian Tracz, Prof. Janusz Chodur

On the basis of available statistics, the following conclusions can be drawn:  The number of persons injured is very similar to the number of accidents and show fluctuations typical of a small number of events  The number of accidents and collisions as well as the number of persons injured at signalized roundabouts in Krakow show a decreasing trend, despite a significant increase in traffic volumes.  The traffic volumes at signalized roundabouts in urban areas are in the range of 4500 – 6500 veh/hour in peak periods (7.00-9.00 and 14.00-17.00)  A certain increase in the number of persons injured can be seen in 2005 due to new rules of designing intergreen periods at signalized roundabouts (with time offset between primary entries and secondary entries – from the storage space at central island – on extension of basic entry) SIGNALIZED TURBO ROUNDABOUTS Considering the extension and increased significance of one of the entries (Kotlarska Street) to signalized Grzegórzeckie Roundabout and the introduction of a fourth tramway entry, the roundabout was transformed into the so-called turbo-roundabout (Figs 14 and 15) with traffic signals. The new shape was to ensure that the island layout accommodates trams within the central island (tramcars 32 m long) and vehicles on the lanes within the roundabout. This design has by much larger internal storage areas within the new roundabout which, as the signalized roundabout with a central island described earlier, also allows traffic control based on a simple quasi 2-phase control. Shared lanes and bus-tram stops were designed.

FIGURE 14 Differences in the design of intersection areas; solid red line– signalized roundabout with a central island (before), dotted green line– new turbo roundabout [Melanowski, 2010]

15 Prof. Marian Tracz, Prof. Janusz Chodur

FIGURE 15 Grzegórzeckie roundabout after reconstruction (photo: W. Majka UM Krakow) The design of a turbo-roundabout is based on the minimum internal radiuses of 25 m (for leftturning traffic) and 30 m, 35 m for straight-through movement. The present capacity with vehicle actuated signals with priority for public transport is approx. 6000 E/h during the afternoon peak. Fig. 16 shows a diagram of traffic intensity at the intersection.

FIGURE 16 Traffic volumes at Grzegórzeckie roundabout

16 Prof. Marian Tracz, Prof. Janusz Chodur

Road incidents data for the period of 2003-2009 at the intersection are presented in Table 3. TABLE 3 Number of accidents and collisions before and after the reconstruction of Grzegórzeckie roundabout ACCIDENTS and COLLISIONS

ACCIDENTS

2003 2004 2005 2006 2007

64 48 53 53 41

11 5 3 2 8

2008

27

2

2009

45

5

YEAR

INJURED

KILLED

ACCIDENTS AND COLLISIONS INVOLVING TRAMS AND BUSES

SIGNAL

3 1 2 1 2

7 8 4 7 1

22 14 18 15 15

2

3

5

3

2

6

PEDESTRIANS RUN INTO

before reconstruction 12 0 7 0 3 0 2 0 11 0 year of reconstruction 2008 2 0 after reconstruction 5 0

The overall number of incidents and traffic signals-related incidents (running into the rear bumper of the preceding vehicle) in comparison with the average number before the reconstruction declined. However, the time span after the reconstruction is too short for any generalizations. The second turbine-signalized roundabout, Kocmyrzowskie, which originally was of a “cigar” shape and had the right-of-way enforced by traffic signs, was rebuilt in 2005 into a signalized turbo roundabout (Fig. 17). The intersection includes a tram junction with tram tracks in all four directions.

FIGURE 17 Kocmyrzowskie roundabout after reconstruction (photo: W. Majka UM Krakow)

17 Prof. Marian Tracz, Prof. Janusz Chodur

Two-phase signal controls were used with phasing as shown in Fig. 18. Stage 1

Stage 2 Ko

m Koc

a wsk

yrzo

sa er

nd

sa er

nd

A n. Ge

A n. Ge

a wsk

rzo cmy

e

m

lin

a Tr

Tr am

a zyc k ńc Bie

Bie

ńc

zyc k

a

e

lin

Stage 1

Stage 2 a wsk

ka

s zow

myr

Koc

sa er

nd .A

sa er

nd .A

n Ge

n Ge

yrzo

m Koc

am

lin

e

Tr am

Tr lin

a Bie ńc zyc k

Bie ńc zyc k

a

e

FIGURE 18 Scheme of phasing at Kocmyrzowskie roundabout

FIGURE 19 Traffic flows at Kocmyzowskie roundabout

Prior to the reconstruction, the intersection was known as a high risk site, for incidents both in terms of the general number of road incidents and accidents, number of accidents involving (hitting) pedestrians, incidents involving municipal transport vehicles and the so-called traffic signals-related incidents. Additionally, in terms of the traffic progression from minor entries and internal storage areas, and also movements of trams (tram tracks occupy the central island) the traffic performance was very poor resulting from limited capacity of the entries. This in turn had a serious impact on traffic safety. The intersection has a high share of left-turning traffic, practically from all entries in the range of 240 – 320 P/h (Fig. 19). The operation time of Kocmyrzowskie roundabout following its reconstruction allows reliable evaluation of changes in road traffic safety (Table 4). As indicated by the data, there has been a marked improvement in road traffic safety both in terms of the overall number of incidents and, above all, in terms of accidents, incidents involving public transport vehicles and the so-called signals-related ones. Thus it can be stated that the effectiveness of the new geometric layout and traffic signals at the intersection are very favorable.

18 Prof. Marian Tracz, Prof. Janusz Chodur

TABLE 4 Number of accidents and collisions before and after the reconstruction of Grzegórzeckie roundabout [Melanowski, 2010] NUMBER OF ACCIDENTS YEAR and COLLISIONS

ACCIDENTS

2000 2001 2002 2003 2004

78 112 102 86 83

11 5 14 11 4

2005

40

5

2006 2007 2008 2009

15 11 26 25

3 1 2 1

INJURED

KILLED

MUNICIPAL TRANSP ORT

SIGNAL

10 1 9 11 4

8 10 11 10 12

19 17 20 21 20

4

4

4

3 0 1 1

3 2 4

3 2 3 2

PEDESTRIANS RUN INTO

before reconstruction 11 0 6 0 15 1 12 0 5 0 year of reconstruction 2005 5 0 after reconstruction 3 0 1 0 2 0 1 0

2

CONCLUSIONS High volumes of left-turn movements favor the use of roundabouts. Under the conditions of heavy traffic intensity at an intersection, roundabouts may operate effectively with traffic signal control. In Poland, signalized roundabouts have been constructed for about 40 years. When used with simple two-phase signals, they facilitate collision-free movement of left-turn vehicles due to the possibility of storage of vehicles within the internal storage space. The principal design problem involves the selection of appropriate parameters of geometry and control which would complement traffic intensity at the intersection. Under the basic arrangement involving two-phase signals, the capacity of the internal storage area must, to a high level of probability, be able to accommodate stopping left-turning vehicles within the intersection so that they do not block the intersection. In the case of the existing signalized roundabouts, an increase of traffic volumes may cause overloading of internal storage areas. This problem can be solved by the use of multiple-phase signals. This entails, however, a decline in the overall capacity of the intersection and deterioration of traffic performance on entries. Signalized roundabouts have much larger capacity than classic unsignalized two-lane intersections, and the rule applies regardless of the signalized design used. The geometry of the Polish type of signalized roundabout, similar to several American two-lane roundabouts (tangential design), as entries are tangential to the central island. Such roundabout can be crossed at high speeds, which increases accident risk. Secondary entries (from storage areas) opened sooner in order to improve progression from the primary entry can lead to an increase in the probability of accidents. The need for improvement in road traffic safety and the efficiency of internal storage areas has led to the construction of signalized turbo roundabouts also in Poland. The first impressions indicate an improvement in the safety after their reconstruction and further point out higher general efficiency even under the conditions of higher accident risk of means of public transport (buses and trams) stopping at bus/tram stops within the intersection.

19 Prof. Marian Tracz, Prof. Janusz Chodur

Bibliography Chodur, Tracz M., J., Gaca, S., Gondek, S., et al., 2004. Manual for Capacity Analyses of Atgrade Intersections. General Directorate of National Roads and Motorways, Warszawa Chodur J., 2005. Capacity Models and Parameters for Unsignalized Urban Intersections in Poland. ASCE, Journal of Transportation Engineering. December 2005, Vol. 131, No. 12 Chodur J., Tracz M., 2008. Roundabout capacity analysis. National Roundabout Conference, Kansas, Transportation Research Board of the National Academies, http://www.teachamerica.com/RAB08/ Melanowski Z. 2010. Is “Turbo Roundabout” with Traffic Lights better than Rotary Intersection with “Central Island”? Research and Technical Papers of Polish Associations for Transportation Engineers in Cracow, series Proceedings, No 92 “Design of Roundabouts - Experiences and New Trends Tracz M., Chodur J., Gaca S. 2001. Guidelines for Design of at-grade intersections [in Polish], Generalna Dyrekcja Dróg Publicznych, Warszawa Tracz M., Chodur J., 2006. Research on capacity of single- and two-lane roundabouts. Proc. of the 5th International Symposium on Highway Capacity and Quality of Service. Nakamura H., Oguchi T. (ed.), Yokohama, Japan, Vol. 2. pp. 479 – 488