signalized intersections; Goodwin/Springfield from the east (pretimed signal), and ... University High School, and Engineering Library pedestrian crossings.
Bashar Al-Omari and Gnani Mahalingam “Using Traffic Simulation for Pedestrian Gap Studies” Highway Research Bulletin, Indian Roads Congress, Number 68, 2003, pp. 157-164.
ABSTRACT The safety of pedestrians crossing mid-block crosswalks depends on the availability of adequate gaps in the traffic streams. Pedestrian gap studies are conducted to measure the predominant pedestrian group size, determine the length of the minimum adequate gap, measure the available gap sizes in the traffic stream, and determine the sufficiency of the available gaps. A case study was taken in the City of Urbana - IL, USA to study two school cross walks bounded by two traffic signals on a major street. The study followed the above steps and found that the available gaps are not sufficient. Different scenarios were suggested to increase the size of the available gaps at the two cross walks by changing the timings, cycle lengths and the types of control (pretimed, semi-actuated and fully actuated) at the two signals to find which scenario would provide the highest number of adequate gaps. It is very difficult to try all the suggested scenarios in the field, so the Traffic Network Simulation Software (TRAF-NETSIM) was used to test all the suggested scenarios. To conduct the pedestrian gap study using NETSIM, one has to watch the traffic animation on the computer screen, and measure the headways between crossing vehicles the same way it is done in the field. After trying all the possible scenarios, It was found that the number of adequate gaps can be increased at most, by making the two signals at the boundaries of the street fully actuated.
INTRODUCTION Pedestrian gap studies are conducted to findout if there are enough gaps in the traffic streams for pedestrians to cross the streets safely. A gap is defined as "the time that elapses from when the rear of a vehicle passes a point on a roadway until the front of the next arriving vehicle (from either direction) passes the same point" (1). In conducting gap studies, the following steps are usually followed (1): 1) Determination of the predominant pedestrian group size: After watching pedestrians for a certain period of time, the predominant pedestrian group size is determined based on the 85th percentile group size.
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2) Calculation of the length of the minimum adequate gap: The minimum adequate gap is defined as: "the time for one or group of pedestrians to perceive and react to the traffic situation and cross the roadway from a point of safety on one side, to a point of safety on the other" (1). It is usually calculated using the following relationship: G = W /S + (N-1)H + R
W here:
(1)
G = minimum adequate gap (sec) W = crossing distance (m) S = walking speed (mt/sec) N = predominant number of rows H = time headway between rows (sec) R = pedestrian startup time (sec)
The following values are usually assumed for S, H, and R respectively: S = 1.22 or 1.07 m/sec, H = 2.0 sec, and R = 3.0 sec.
3) Field Measurement of the gap sizes in the traffic stream: A field measurement of the gap sizes is conducted to find the number of adequate gaps (longer than the calculated minimum safe gap).
4) Determination of the sufficiency of the adequate gaps: MUTCD (2) states that, a traffic signal may be warranted, when the number of adequate gaps in the traffic stream, when school children are crossing, is less than the number of minutes in the same period. Thus, the number of adequate gaps for school crossings, should not be less than one per minute.
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STUDY LOCATIONS The two pedestrian crossings (at the University High School and Engineering Library) are located in the City of Urbana - IL, USA, at Springfield Avenue, and bounded by two signalized intersections; Goodwin/Springfield from the east (pretimed signal), and W right/Springfield from the west (fully actuated signal). The study area is as shown in Figure 1.
STUDY OBJECTIVES The purpose of this study is to findout if there are enough pedestrian gaps, at the University High School, and Engineering Library pedestrian crossings. The two crossings are bounded by two signalized intersections. If no adequate gaps are found, the study will try different scenarios by changing the signals timings, cycle lengths and types of control (pretimed versus actuated), to find out which scenario would provide the highest number of adequate gaps.
PEDESTRIAN VOLUMES The volumes of pedestrians at the two crossings were counted during the AM, Noon and PM pedestrian peak periods during a regular week day. It was found that the highest number of pedestrians occurs during the noon peak (11:45-12:00 PM). The study will concentrate on this peak period, because it is the worst condition.
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N
W right St.
University High School
Goodwin St.
Springfield Avenue
Engineering Library
Figure 1. A Sketch Shows the Study Locations
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FIELD GAP STUDIES The field pedestrian gap studies were conducted for the two crossings as follows: a) University High School Crossing: A trip was made to the field, and pedestrian data was collected as shown in Table 1 below: Table 1. Pedestrian group sizes for University High School Crossing # of Rows
Frequency
Cumulative
1
29
29
2
9
38
3
3
41
4
1
42
N = 0.85*42 = 35.7 (2 rows), H=2.0 sec, R=3.0 sec, S=1.07 m/sec, W =9.14 m. G = 9.14/1.07+(2-1)*2+3 = 14.0 sec. The number of adequate gaps ( 14.0 sec) =7 Since the time interval is 15 minutes, then based on the criteria of one gap per minute, the minimum number of adequate gaps should be equal to 15 gaps. The available number of adequate gaps = 7 which is not enough.
b) Engineering Library Crossing: A trip was made to the field, and pedestrian data was collected as shown in Table 2 below: Table 2. Pedestrian group sizes for Engineering Library Crossing # of Rows
Frequency
Cumulative
1
69
69
2
20
89
3
8
97
4
4
10 1
5
1
10 2
6
N = 0.85*102 = 86.7 (2 rows), H=2.0 sec, R=3.0 sec, S=1.07 m/sec, W =7.62 m. G = 7.62/1.07+(2-1)*2+3 = 13.0 sec. The number of adequate gaps ( 13.0 sec) = 11 Since the time interval is 15 minutes, then based on the criteria of one gap per minute, the minimum number of adequate gaps should be equal to 15 gaps. The available number of gaps = 11 which is not enough.
CHECKING SIGNAL WARRANTS There are two signal warrants related to pedestrians according to MUTCD (2):
"I) W arrant 3, Minimum Pedestrian Volume: The minimum pedestrian volume warrant is satisfied when, for each of any eight hours of an average day, the following traffic volumes exist: 1. On the major street, 600 or more vehicles per hour enter the intersection (total of both approaches); or where there is a raised median island 1.2 m (4 feet) or more in width, 1,000 or more vehicles per hour (total of both approaches) enter the intersection on the major street; and 2. During the same eight hours as in paragraph (1) there are 150 or more pedestrians per hour on the highest volume crosswalk crossing the major street….
II) W arrant 4, School Crossing: A traffic control signal may be warranted at an established school crossing, when a traffic engineering study of the frequency and adequacy of gaps in the vehicular traffic stream as related to the number and size of groups of school children at the school crossing shows that the number of adequate gaps in the traffic stream during the period when the children are using the crossing is less than the number of minutes in the same period ….”.
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The above two warrants were tested as follows: I) Minimum Pedestrian Volume: a. the major street traffic volume has a traffic volume of more than 600 vph (both directions) for continuous eight hours, so the first condition is satisfied. b. the pedestrian volume does not exceed 150/hr except for one 15 minute time interval in the PM peak for the University High School crossing and two 15 minutes time intervals in the Noon peak for the Engineering Library crossing. So the second condition for this warrant is not satisfied. II) School Crossing: The two locations did not have enough number of gaps during the 15 minutes of interest. So according to this criteria, signals are warranted. Since the two crossings do not have enough number of adequate gaps, and the limited fund does not make the signalization of the two crossings an option, the study will concentrate on trying to increase the number of gaps by changing the settings of the two signals that control the traffic arrivals at the two crossings. Since this can not be easily done in the field, then traffic simulation will be used to study different scenarios.
TRAFFIC SIMULATION MODELS There are many traffic simulation models that are being used nowadays such as TRANSYT-7F, PASSERII, SOAP and TRAF-NETSIM. TRAF-NETSIM
has m any
features that makes it superior to the other programs. It keeps track of the time and position of each vehicle in the network and can simulate all types of control including yield signs, stop signs, fixed time signals, actuated signals and signals with different cycle lengths (3, 4).
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NETSIM GAP STUDIES NETSIM simulation was used to conduct gap studies for different scenarios.
T he
required geometric, traffic and signal control data were collected from the field and used as inputs to the software using its standard procedure (5). The gap study is done using NETSIM, the same way it is done in the field. The person watches the traffic animation on the computer screen, and measures the headways between crossing vehicles while watching real time NETSIM animation, the same way it is done in the field. NETSIM gap studies were made for the following three scenarios: I)
II)
Existing Condition: a)
Actuated W right/Springfield.
b)
Pretimed Goodwin/Springfield.
Both signals are pretimed with coordination.
The optimal cycle lengths and timings were obtained for W right/Springfield signal using the HCM procedure (6). The HCS was then used to find the optimal timing for Goodwin/Springfield with the same cycle length obtained before. Then, PASSER was used to find the best coordination between the two signals.
III) Both signals are actuated. Even though Goodwin/Springfield signal is pretimed, it is capable of actuation. This scenario considers the actuation of the two traffic signals. By using NETSIM simulation, and making five runs for each scenario with different seed random numbers as suggested by Ajay Rathi etal (7), the number of adequate gaps were obtained for the two crossings, as shown in Table 3 for University High school crossing, and in Table 4 for the Engineering Library crossing.
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Table 3. NETSIM Gap Studies at the University High School Pedestrian Crossing. Scenario
Run
G a p s 1 4
1 3
1 2
1 1
1 0
I
1
5
8
9
11
20
2
6
8
12
14
23
3
6
9
12
14
22
4
8
9
15
18
28
5
9
10
15
18
22
Avg
6 .8
8 .8
1 2 .6
1 5 .0
2 3 .0
1
4
7
10
14
17
2
6
9
12
17
21
3
6
8
15
18
23
4
9
10
15
18
25
5
8
10
13
18
20
Avg
6 .6
8 .8
1 3 .0
1 7 .0
2 1 .2
1
7
10
12
17
23
2
12
14
17
25
27
3
9
12
14
17
25
4
7
9
11
21
27
5
5
8
12
16
24
Avg
8 .0
1 0 .6
1 3 .2
1 9 .2
2 5 .2
II
III
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Table 4. NETSIM Gap Studies at the Engineering Library Pedestrian Crossing. Scenario
Run
G a p s 1 4
1 3
1 2
1 1
1 0
I
1
6
8
10
18
22
2
10
11
17
19
30
3
12
17
19
23
27
4
10
12
15
16
25
5
8
13
15
15
18
Avg
9 .2
1 2 .2
1 5 .2
1 8 .2
2 4 .4
1
7
11
12
17
20
2
9
15
17
20
24
3
5
9
11
14
22
4
4
7
12
16
20
5
6
7
11
17
23
Avg
6 .2
9 .8
1 2 .6
1 6 .8
2 1 .8
1
10
11
14
16
21
2
10
13
18
23
26
3
11
12
12
16
24
4
15
17
22
25
30
5
7
8
11
22
27
Avg
1 0 .6
1 2 .2
1 5 .4
2 0 .4
2 5 .6
II
III
By averaging the five runs for each scenario, the following results were obtained for different numbers of minimum gaps:
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Table 5. Number of Gaps ( G) for University High School Crossing Gap, G (sec)
Scenario I
Scenario II
Scenario III
14
7
7
8
13
9
9
11
12
13
13
13
11
15
17
19
10
23
21
25
Table 6. Number of Gaps ( G) for Engineering Library Crossing Gap (sec)
Scenario I
Scenario II
Scenario III
14
9
6
11
13
12
10
12
12
15
13
15
11
18
17
20
10
24
22
26
It can be seen that none of the scenarios provide enough number of adequate gaps ( 15). However, the number of adequate gaps can be increased at most, by making the two signals at Goodwin/Springfield and W right/Springfield actuated.
CONCLUSIONS & RECOMMENDATIONS It was found that there are no enough safe pedestrian gaps at the University High School and Engineering Library pedestrian crossings. The two pedestrian signal warrants (minimum pedestrian volume and school crossing) were studied, and the second warrant was found to be satisfied, indicating a need for signalization. It was also
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found that the number of adequate gaps can be increased at most, by making the two signals at Goodwin/Springfield and W right/Springfield fully actuated.
Acknowledgement: The authors are very grateful for the sponsorship, data collection and facilities offered by the Champaign-Urbana Urbanized Area Transportation Study. REFERENCES 1. MANUAL OF TRANSPORTATION ENGINEERING Transportation Engineers, New Jersey 1994.
STUDIES,
Institute
of
2. USDOT (1988). Manual on Uniform Traffic Control Devices for Streets and Highways, Federal Highway Administration, W ashington, D.C., PP 4C-4 to 4C-5. 3. W ong, Shui-Ying, TRAF-NETSIM: How it works, W hat it does”, Institute of Transportation Engineers, Vol. 60, No. 4, pp. 22-27, April, 1990. 4. Sarker, Mohsin J., Hirotaka Koike & Akinori Morimoto, “Assessment of Gap Actuated Push Button Signal by Using Traffic Simulation Model”, Presented at the Transportation Research Board Conference, W ashington D.C., January 1999. 5. TRAF-NETSIM USER'S MANUAL, U.S. Dep. of Transportation, Federal Highway Administration, Publication # FHW A-RD-92-060, May 1992. 6. Transportation Research Board Special Report 209: Highway Capacity Manual, Transportation Research Board, W ashington, D.C., 1994 Update. 7. Rathi, Ajay K. and Santiago, Alberto J., “Identical traffic streams in the TRAFNETSIM simulation program” Traffic Engineering & Control, Vol. 31, No. 6, pp. 351-355, June 1990.
