Queue Jump Lane, Transit Signal Priority, and Stop Location: Evaluation of Transit Preferential Treatments using Microsimulation
Burak Cesme
Selman Z. Altun
Barrett Lane
Submitted to the Transportation Research Board for presentation and publication
July 14, 2014; revised November 14, 2014
Word Count: 4,741 words + 11*250 words (10 figures + 1 table) = 7,491 words
1 Abstract
2 Transit preferential treatments offer the potential to improve transit travel time and reliability.
3 However, the benefits of these treatments vary greatly depending on the specific characteristics of the
4 study area, including turning movement and pedestrian volumes, signal timing parameters, and transit
5 stop location. To evaluate the performance of preferential treatments, practitioners typically rely on
6 microscopic simulation models, which require a considerable amount of effort, or review previous
7 studies, which may reflect a bias to the area characteristics. This paper develops a test-bed and a
8 planning-level framework to help practitioners determine the benefits offered by various preferential
9 treatments without developing a detailed simulation model. To evaluate preferential treatment
10 benefits, the authors performed extensive simulation runs under various scenarios at an isolated
11 intersection using VISSIM. The analyses show that the greatest benefit comes from relocating a near-
12 side stop to a far-side stop, in which far-side stops can reduce delay up to 30 seconds per intersection.
13 The highest savings that could be obtained with a queue jump lane is approximately 9 seconds per
14 intersection. As the amount of right-turns increase along with the number of conflicting pedestrians, the
15 benefit of queue jump lane disappears. Transit signal priority with 15 seconds of green extension and
16 red truncation can offer up to 19 seconds of reduction in delay, where the benefits become more
17 pronounced with high volume to capacity (v/c) ratio. With low v/c ratio, granting 10 seconds of green
18 extension without red truncation provide very marginal benefits; only 2 seconds delay reduction per
19 intersection.
1 Introduction
2 Transit preferential treatments such as queue jump lanes, bus-only lanes, and transit signal priority (TSP)
3 have the potential to improve transit travel times and reliability in a mixed-traffic environment, which in
4 turn reduce waiting time of passengers, unnecessary fleet size, and increase ridership [1] [2]. The
5 benefits of these treatments, however, greatly depend on the area type characteristics as well as the
6 physical configurations of the street network [1] [3] [4]. Transit stop location, signal timing parameters,
7 turning movement and pedestrian volumes affect operations in an interdependent and non-linear
8 manner. To evaluate the benefits, at the planning level, practitioners review previous studies and other
9 resources to estimate the benefit that could be expected at their specific location. Yet, many of these
10 previous studies analyze cases with unique configurations or systems of actual intersections, which, in
11 turn, reflect a bias towards the specific parameters that were used. Microsimulation models, if
12 calibrated properly, can reflect site-specific conditions and provide more reliable results. However, the
13 development of simulation models can be cumbersome and may require many hours of modeling.
14 The objective of this study is to develop a test-bed and a planning-level framework for
15 practitioners to determine the potential benefit offered by various preferential treatments without
16 developing a detailed microsimulation model. To determine preferential treatment savings, the authors
17 performed over 5,000 simulation runs at an isolated intersection using a microsimulation model, VISSIM,
18 by changing one parameter at a time. These include the “input” parameters such as traffic volumes,
19 green to cycle ratio (g/C), pedestrian volumes, and transit dwell times in combination with the
20 “configurable” variables such as the location of a transit stop and the length of a queue jump lane. The
21 results of this study will provide answers to the following questions:
22 What is the expected delay reduction with queue jump lanes?
23 What is the expected delay reduction with TSP?
1
1 How do stop location (e.g., far-side vs. near-side) and dwell time affect bus delay?
2 Because our research included sensitivity runs with many factors that affect the operations in
3 real life, it allows practitioners to obtain a close-to-reality measurement of benefits before weighing
4 them off against the costs and the potential impacts of these treatments. The authors envision this
5 research as a step towards developing transit preferential treatment warrants.
6 The remainder of this paper is organized as follows. The next section provides definition and
7 literature review on preferential treatments as well as bus stop location. It is followed by the description
8 of the applied methodology and simulation results for the preferential treatments. The last section of
9 the paper presents the main conclusions.
10 Queue Jump/Bypass Lanes
11 Queue jump and bypass lanes allow the transit vehicle to skip the queue either all together or at least
12 partially. Full skipping occurs when no other vehicles are allowed to enter the queue jump/bypass area.
13 Partial skipping occurs when right-turning vehicles are allowed to use the queue jump/bypass lane.
14 Figure 1 shows the difference between a queue jump lane and a bypass lane [5].
2
1
2 Figure 1 – Queue Jump and Queue Bypass Lane [5]
3 Even though queue jump and bypass lanes are the common terms used in the industry, the authors
4 believe that the names are not self-explanatory and cause confusion among practitioners. Therefore, for
5 the rest of this paper, “one-sided queue jump lane” and “two-sided queue jump lane” will be used for
6 queue jump lane and queue bypass lane, respectively.
7 Transit Signal Priority
8 Transit signal priority (TSP) gives extra green time or less red time to transit phases at a signalized
9 intersection to reduce transit delay associated with traffic signals [3]. It also reduces the variability in
10 running times by reducing signal delays. Running time variability is a major challenge for transit agencies
11 as it not only causes overcrowding on buses, but also increases the 90th percentile running time that is
3
1 often used to determine scheduled running plus recovery time. This, in turn, determines fleet size and
2 thereby operating cost [2].
3 Bus Stop Location
4 Transit stops in urban areas are either at mid-block locations or at near-side or far-side of intersections
5 [6]. Intersections are generally preferred over mid-block locations as they typically come with pedestrian
6 crossing accommodations and provide better access to side streets.
7 Literature Review for Transit Preferential Treatments
8 Transit Capacity and Quality of Service Manual (TCQSM) and Transit Cooperative Research Program
9 (TCRP) Report 118 - Bus Rapid Transit Practitioner’s Guide - provide some guidance regarding the
10 operations of one-sided and two-sided queue jump lanes [5] [7]. TCRP Report 118 estimates travel time
11 savings in the range of 5 to 15 percent with one-sided queue jump lanes [7].
12 Zhou and Gan evaluated one-sided queue jump lanes under different TSP strategies, traffic
13 volumes, dwell times, and bus stop locations [8]. Their results showed that special bus phase, which
14 allows buses to merge back into the mainline easily, is necessary for one-sided queue jump lanes to be
15 effective. Moreover, right-turn volumes were found to have an insignificant impact on bus delay.
16 Zlatkovic et al. [9] evaluated the individual and combined effects of one-sided queue jump lanes
17 and TSP on performance of a Bus Rapid Transit (BRT) system in West Valley City, Utah. 13 signalized
18 intersections were analyzed using VISSIM. Simulation results showed the combined queue jump lanes
19 and TSP scenario yielded highest benefits: 13-22 percent reduction in BRT travel times and 22 percent
20 increase in BRT speed.
21 Lahon [10] evaluated the benefits and impacts of TSP and one-sided queue jump lanes for the
22 BRT system in the City of Pleasanton, California. Six signalized intersections were modeled in VISSIM.
23 Results indicated that TSP and queue jump lanes reduced delay by 30 percent along the corridor. It was
4
1 also found that TSP and queue jump lanes are most beneficial when congestion levels are higher for the
2 corresponding through movement.
3 Altun and Furth [2] developed a uniform delay model to predict transit delay reduction at a
4 signalized intersection due to TSP. They demonstrated the relationship between benefits of green
5 extension and red truncation strategies and their probability of occurrence during a signal cycle. Figure 2
6 shows this uniform delay model, where “r” is the red duration of mainline (bus movement), “C” is the
7 cycle length, “x” is the green extension amount, “e” is the early green (red truncation) amount, “s” is the
8 saturation flow rate, “v” is the volume, and “k” is a random variable between 0 and 1 that represents
9 the random arrival of a bus at any point in the signal cycle.
10 Delay 11
푠−푣 푟−푒−푥 푠 12 Average Delay with Priority = 푠 (푟 − 푒) − 푥 r 2퐶 푠−푣 13
14 r-e Delay without priority = 푟 − 푠−푣 푘퐶 푠 15
16 Delay with priority = (푟 − 푒) − 푠−푣 푘퐶 17 푠
18 k.C 19 푠 푠 (푟 − 푒)( ) 푟( ) x 푠−푣 푠−푣 C 20 21 0 k 1 22 23 Figure 2 - Uniform Delay Model to Estimate Transit Signal Priority Benefits [2]
24 Furth et al. [11] explored the marginal impact (i.e., change in bus delay, defined as “average net
25 delay”) of bus stop location on bus delay. A deterministic model, accounting for deceleration,
5
1 acceleration, and queue interference, was developed at signalized intersections. The results showed
2 that for far-side stops, average net delay is approximately -0.5 seconds, while for near-side stops,
3 average net delay is about 10 seconds. Moreover, the results indicated that, with respect to setback for
4 near-side stops, the average net delay is worst when the setback is small (25 to 100 feet) since queues
5 block buses from reaching a stop line. Larger setbacks reduce delay by minimizing the chance that a
6 queue will block the stop. Finally, with a bus-only lane, near-side stops yield negative net delay and are
7 better than far-side stops. However, the study did not quantify the marginal impact of variable dwell
8 times on bus delay.
9 TCRP Report 19 - Guidelines for the Location and Design of Bus Stops - developed guidelines for
10 designing and locating bus stops [6]. The report performed a comparative analysis of bus stop locations
11 and lists the advantages and disadvantages of far-side, near-side, and mid-block stops while considering
12 the impacts on pedestrian safety, traffic safety, intersection capacity, and bus delay. However, the bus
13 delay results were not quantified.
14 Finally, TCQSM [5] described bus preferential treatments at intersections including transit TSP,
15 queue jump, curb extensions, and boarding islands. However, the discussion did not provide any
16 quantifiable results on bus delay effects.
17 Methodology
18 To evaluate the potential benefits of transit preferential treatments and the impact of stop location on
19 bus delay, a simulation test-bed was developed in VISSIM. The test intersection included the junction of
20 a four-lane road with a two-lane road, with left turn bays on all approaches (Figure 3). A bus line
21 operating in mixed traffic with 6-minute headway was introduced in the simulation model.
6
1
2 3 Figure 3 - Test Intersection Layout
4 The intersection operated by a fixed-time control with a 100-second cycle length. Keeping the
5 volumes constant, green time for the “bus phase” was adjusted to test different volume to capacity ratio
6 (v/c) for the corresponding through movement.
7 In VISSIM, transit vehicles enter the network based on the schedule provided by the user.
8 Therefore, there exists no randomness in transit vehicle generation. To introduce a random arrival
9 process for transit vehicles, a “dummy” bus stop was created at the beginning of the bus route. Because
10 the intersection operated with a 100-second cycle length, a uniform distribution with minimum zero
11 seconds and maximum 100 seconds was selected for the dwell time at the dummy stop so that buses
12 arrive at the intersection at any time in a cycle.
13 Conventional TSP tactics (i.e., green extension and red truncation) were applied to evaluate the
14 TSP benefits. 10 seconds and 15 seconds of green extension and red truncation were considered for the
15 bus phase. The control logic for TSP was modeled using VISSIM’s vehicle actuated programming (VAP)
7
1 language, which enables simulating custom traffic signal control, including fully-actuated signal control
2 and TSP [12].
3 For each transit preferential treatment, a “No Build” and a “Build” scenario (Build includes the
4 preferential treatment) were modeled in VISSIM. 20 simulation runs with different random seeds were
5 performed for each scenario. Each simulation run lasted 3,600 seconds following a 300-second warm-up
6 period, thus providing 10 bus events per run. Therefore, each scenario includes 200 data points (20 runs
7 x 10 buses/run). The benefits associated with each preferential treatment were calculated using Net
8 Delay where the calculation of net delay is given by:
9 10 Net Delay = Build Travel Time – No Build Travel Time (1)
11 12 Therefore, a positive net delay means an increase in bus delay while a negative net delay
13 indicates bus delay reduction.
14 Results for Two-Sided Queue Jump Lane Scenario
15 Base Case: Varying Right-Turns without Conflicting Pedestrians
16 Two-sided queue jump lane was initially tested with no conflicting pedestrians and variable right turn
17 volumes. Figure 4 shows intersection configuration under No Build and Build conditions and presents
18 net delay as a function of bus phase v/c with the hourly right turn volume when conflicting pedestrian
19 volume is zero. Note that for all the scenarios, the length of the queue jump lane was selected based on
20 the 95th percentile queue length for the bus phase.
8
1 1. No Build – No Queue Jump Lane 2. Build – With Two-Sided Queue Jump Lane 2
3 2.0
0.0 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 RT = 300
-2.0
-4.0
RT = 200 Net Delay (s) Delay Net -6.0
-8.0 RT = 100 RT = 0 -10.0 Bus Phase v/c Ratio 4
5 Figure 4 – Two-Sided Queue Jump Lane Net Delay (s) versus Bus Phase v/c Ratio: Variable Hourly Right 6 Turn Volume (RT) Without Pedestrians 7 8 Results indicate that net delay associated with queue jump lane approaches zero as v/c ratio for
9 the bus phase decreases (Figure 4). In other words, the less congested the approach, the smaller the
10 benefits. Also, the benefit decreases as the right turning volume increases, because right turning
11 vehicles are allowed to use the queue jump lane, thereby interfering with the bus operations. With
9
1 moderate to high bus phase v/c ratio (v/c greater than 0.7), the benefits start to be more pronounced.
2 Results show that approximately 10 second reduction in bus delay is possible when v/c is higher than 0.9
3 and right turn volume is lower than 100 vehicles per hour.
4 Sensitivity to the Length of Queue Jump Lane
5 Further experiments were conducted with variations in the length of queue jump lane. Variable lengths
6 considered in the analysis included 95th, 85th, 50th, and 35th percentile bus approach queue length. No
7 right turning vehicles and pedestrians were introduced in the model. Results are shown in Table 1.
8 Table 1 - Two-Sided Queue Jump Lane Net Delay (s) versus Bus Phase v/c Ratio under Different Queue 9 Jump Lane Lengths 10 QUEUE JUMP LANE NET DELAY (s) Bus Phase v/c Ratio 95th Percentile 85th Percentile 50th Percentile 35th Percentile 0.90 -9.2 -8.9 -8.4 -7.9 0.75 -6.9 -6.7 -6.4 -6.1 0.58 -4.3 -4.2 -3.9 -3.7 0.48 -2.1 -2.1 -1.9 -1.8 0.41 -1.7 -1.6 -1.6 -1.5 11 12 Simulation results indicate that having a queue jump lane that corresponds to the 95th percentile queue
13 instead of 35th percentile queue reduces bus delay by 1.3 seconds when bus phase v/c ratio is 0.90. The
14 benefit of longer queue jump lanes is fairly small for all bus phase v/c ratios.
15 Effect of Pedestrians Conflicting with Right-Turns
16 Two-sided queue jump lane was also tested with variable right turning volume and pedestrians that are
17 in conflict with the right turn movement. Two different No Build (base) scenarios were introduced to
18 analyze the impact of pedestrians and right-turning vehicles on queue jump lane benefits. The first No
19 Build scenario assumed operation with an exclusive right-turn lane (Figure 5) while the second No Build
20 scenario assumed no exclusive right turn lane where right turning vehicles share the lane with the
21 through vehicles (Figure 6).
10
1 Queue jump lane net delay results as a function of bus phase v/c ratio when No-Build includes
2 an exclusive right-turn lane are presented in Figure 5.
11
1 1. No Build – No Queue Jump Lane 2. Build – With Two-Sided Queue Jump Lane 2
3 4 RT=100 RT=200
25.0 25.0 Ped=0 Ped=0 20.0 20.0 Ped=50 Ped=50 Ped=150 15.0 15.0 Ped=150 Ped=300 10.0 Ped=300 10.0 Ped=500 Ped=500
5.0 5.0
Net Delay Net Delay (s) Net Delay (s) 0.0 0.0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -5.0 -5.0
-10.0 -10.0 Bus Phase v/c Ratio Bus Phase v/c Ratio
25.0 Ped=0 20.0 Ped=50 Ped=150 15.0 Ped=300 Ped=500 10.0
5.0 Net Delay Net Delay (s) 0.0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -5.0
-10.0 5 Bus Phase v/c Ratio
6 RT=300
7 Note: The figure does not include results when the right-turn movement operates above capacity due to 8 the influence of heavy pedestrian volumes. 9 10 Figure 5: Two-Sided Queue Jump Lane Net Delay (s) versus Bus Phase v/c Ratio under Different 11 Pedestrian and Right Turn (RT) Volume, (a) RT=100, (b) RT=200, (c) RT=300
12
1 Results show that with the exclusive right-turn lane under the No Build, the benefit of queue
2 jump lane disappears when hourly pedestrian volumes are greater than 150 under all right turn demand
3 scenarios. Except for the low pedestrian interference and low right turn volume, the benefit is very
4 small, less than 5 seconds. Another important finding is that when there is moderate to heavy
5 pedestrian activity (e.g., more than 300 pedestrians), forcing buses to use the exclusive right-turn lane
6 to bypass the through queue may cause substantial increase in bus delay, in particular when the right-
7 turn movement is heavy.
8 Figure 6 provides queue jump lane net delay results when the No Build scenario does not
9 include an exclusive right-turn lane. Note that given the same through and right-turn volumes, bus
10 phase v/c ratios are different under the No Build and Build scenarios since Build scenario introduces a
11 right-turn pocket, which in turn reduces through approach volume. For example, a bus phase v/c ratio of
12 0.9 in the Build scenario corresponds to a No Build v/c ratio of 1.0 when right turn volume is 100
13 vehicles, a v/c ratio of 1.09 when right turn volume is 200, and a v/c ratio of 1.18 when right turn
14 volume is 300. The bus phase v/c ratios shown in Figure 6 are based on Build conditions. Results for v/c
15 ratio of 0.9 are not included since it resulted in overcapacity under No Build.
13
1 1. No Build – No Queue Jump Lane 2. Build – With Two-Sided Queue Jump Lane 2
3
4 RT=100 RT=200
4.0 4.0
2.0 2.0
0.0 0.0 0.3 0.4 0.5 0.6 0.7 0.8 0.3 0.4 0.5 0.6 0.7 0.8 -2.0 -2.0 Ped=0 -4.0 -4.0 Ped=0
-6.0 Ped=50 Ped=50 Net Delay Net Delay (s)
Net Delay Net Delay (s) -6.0 Ped=150 Ped=150 -8.0 -8.0 Ped=300 Ped=300 -10.0 -10.0 Ped=500 Ped=500 -12.0 Bus Phase v/c Ratio -12.0 Bus Phase v/c Ratio
4.0
2.0
0.0 0.3 0.4 0.5 0.6 0.7 0.8 -2.0
-4.0 Ped=0
-6.0 Ped=50 Net Delay Net Delay (s) Ped=150 -8.0 Ped=300 -10.0 Ped=500 -12.0 5 Bus Phase v/c Ratio
6 RT=300
7 Note: The figure does not include results when the right-turn movement operates above capacity due to 8 the influence of heavy pedestrian volumes. 9 10 Figure 6: Two-Sided Queue Jump Lane Net Delay (s) versus Bus Phase v/c Ratio under Different 11 Pedestrian and Right Turn (RT) Volume, (a) RT=100, (b) RT=200, (c) RT=300
14
1 Results show that when the No Build scenario does not have an exclusive right-turn lane,
2 introducing queue jump lane typically results in significant savings when bus phase v/c ratio is above 0.5,
3 where some of this benefit can be attributed to an increase in approach capacity as a result of the added
4 right-turn pocket. However, low bus phase v/c ratio and high pedestrian demand activity (e.g., more
5 than 300 pedestrians per hour) could cause marginal increase in bus delay (less than 2 seconds).
6 Results for Transit Signal Priority Scenario
7 Net delay under different bus phase v/c ratio is shown in Figure 7. Not surprisingly, results show that
8 TSP becomes more effective as the bus phase experiences more congestion. For example, with 10
9 seconds of green extension and red truncation, bus delay reduction per intersection is about four
10 seconds when v/c ratio is 0.4, while the delay reduction becomes more than 12 seconds when v/c ratio
11 is 0.9. With the maximum time span for TSP tactics of 15 seconds, the application of green extension
12 and red truncation provide significant reductions in bus delay (ranging from 6 to 18 seconds, depending
13 on the bus phase v/c ratio).
14 Similar to the results provided by Furth et al. [13], the findings suggest that TSP benefits would
15 be higher for buses that use minor traffic streams (e.g., buses traveling on cross street or making a left-
16 turn) than for those on the main street, because v/c ratios for minor streams are typically higher.
17 Additionally, the TSP benefits would be less than what is reported in Figure 7 if buses are able to follow
18 signal coordination between intersections. Our results reflect a case where a bus can arrive at an
19 intersection any time in the cycle, either as a result of fully actuated operation where the cycle length is
20 variable or due to variable dwell times at bus stops between intersections under coordinated operation.
21 Further research is necessary to derive adjustment factors for TSP benefits when the bus operation is
22 such that buses can take advantage of signal coordination (e.g., short segments without stops).
15
1 1. No Build – No TSP 2. Build – With TSP 2
3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 0.0
-4.0 -4.0
-8.0 -8.0
Green Extension Net Delay Net Delay (s)
Net Delay Net Delay (s) -12.0 -12.0 Green Extension and Red Truncation Green Extension -16.0 -16.0 Green Extension and Red Truncation
-20.0 -20.0 Bus Phase v/c Ratio Bus Phase v/c Ratio 4
5 (a) : 10 sec (b) : 15 sec
6 Figure 7: Green Extension and Red Truncation Net Delay (s) versus Bus Phase r/C Ratio, (a) = 10 7 seconds of Green Extension and Red Truncation, (b) = 15 seconds of Green Extension and Red 8 Truncation 9 10 To verify the uniform delay model developed by Altun et al. [2], which evaluates TSP savings at a
11 signalized intersection, the savings (with different extension and red truncation parameters) obtained
12 from the simulation model were compared to the uniform delay model results (Figure 8).
16
20.0 20.0 45⁰ Green Extension: RMSE = 0.43s, E[Model/VISSIM] = 0.95 Green Extension: RMSE = 0.43s, 18.0 18.0 E[Model/VISSIM] = 1.00 Green Extension and Red Truncation: RMSE = 0.68s, E[Model/VISSIM] = 1.07 16.0 16.0 45⁰ Green Extension and Red Truncation: RMSE = 0.75s, 14.0 14.0 E[Model/VISSIM] = 1.05 12.0 12.0 10.0
10.0 MODEL MODEL 8.0 8.0 6.0 6.0 4.0 4.0 2.0 2.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 VISSIM VISSIM 1
2 Figure 8: Expected Transit Signal Priority Saving (s) for the Delay Model versus Simulation Experiments 3 4 Results show the good agreement in expected savings when only green extension was granted.
5 The root-mean-square error (RMSE) when the maximum allowed green extension was 10 and 15
6 seconds was 0.43 seconds in both scenarios. When green extension was applied with red truncation, the
7 model slightly overestimates the savings where the difference tends to increase with higher red
8 truncation times and bus phase v/c ratio. When the maximum red truncation time was 10 seconds,
9 RMSE was calculated as 0.68 seconds, and it increased to 0.75 seconds with 15 seconds of red
10 truncation time. Moreover, uniform model delay results are within 7 percent of the simulation results in
11 all TSP scenarios. Because these errors are relatively low, it can be concluded that the uniform delay
12 model is a reliable indicator of TSP benefits.
13 Results for Near-Side versus Far-Side Stop Scenario
14 To evaluate the impacts of stop location on bus delay, stop setback distance (i.e., the distance between
15 the stop bar and a near-side stop) was set as a variable. The net delay for near-side stops with different
17
1 setback distances was compared to far-side stop. Figure 9 shows net delay relationship for various stop
2 locations against the red to cycle length (r/C) ratio. Note that r/C ratio was used rather than bus phase
3 v/c ratio since the authors believe that r/C ratio is a more relevant parameter that determines whether
4 a bus can clear the intersection after serving a near-side stop. It was assumed that expected dwell time
5 (tdwell) at the bus stop is 20 seconds in all scenarios, corresponding to a tdwell/C ratio of 0.2. The No Build
6 scenario considered a midblock stop that does not interfere with the signal queues (i.e., not under the
7 influence of signal delay, Figure 9).
18
1 1. No Build – Midblock Stop 2. Build – Near Side and Far Side Stops
S = 200’ S = 100’ S = 0’
2 3 35.0 Near Side, S=0ft 30.0 Near Side, S=100ft 25.0 Near Side, S=200ft
20.0
Far Side 15.0
10.0 Net Delay (s) Delay Net 5.0
0.0 0.3 0.4 0.5 0.6 0.7 -5.0
-10.0 4 Bus Phase r/C Ratio
5 S: Setback Distance (feet)
6 Figure 9: Near-Side and Far-Side Stop Net Delay versus Red Ratio (r/C) for the Bus Phase
7 Results show that far-side stop net delay is just below zero and remains roughly constant for
8 different red ratios. However, near-side stop with no setback distance (i.e., S=0) increases bus delay
9 significantly, particularly for high red ratios. When red ratio is 0.66 (corresponding to a bus phase v/c
19
1 ratio of 0.9), for example, a near-side stop increases bus delay by more than 30 seconds. This can be
2 attributed to the fact that a bus may have to make “triple stops” when serving a near-side stop. The first
3 stop occurs because queue in front of a bus blocks the stop. The second stop is to serve passengers, and
4 finally a third stop may happen if a bus misses the green signal while serving the stop. With non-zero
5 setback (e.g., S= 100 feet or 200 feet), increase in bus delay is much smaller, because larger setbacks
6 reduce the probability that a queue will block the stop. Moreover, if the red ratio is high, certain portion
7 of the dwell time may overlap with the red signal, further reducing delay for near-side stops with non-
8 zero setback distances.
9 We also analyzed the impact of variable dwell times on bus delay. Figure 10 shows net delay for
10 a variety of bus stop locations, bus stop setbacks, tdwell/C ratio, and red ratio. Results show that when
11 tdwell/C is 0.60, increase in bus delay under near-side stop with zero setback is not as high as lower tdwell/C
12 ratio, because a higher portion of the dwell time overlaps with the red signal. Moreover, near-side stops
13 with non-zero setback provide comparable results with the far-side stop when tdwell/C is 0.60.
14 30.0 30.0 Near Side, S=0ft Near Side, S=0ft 25.0 25.0 Near Side, S=100ft Near Side, S=100ft 20.0 20.0 Near Side, S=200ft Near Side, S=200ft Far Side 15.0 15.0 Far Side 10.0
10.0 Net (s) Delay Net (s) Delay 5.0 5.0 0.0 0.3 0.4 0.5 0.6 0.7 0.0 -5.0 0.3 0.4 0.5 0.6 0.7 -5.0 -10.0 15 Bus Phase r/C Ratio Bus Phase r/C Ratio
16 (a): tdwell/C = 0.40 (b): tdwell/C = 0.60
17 Figure 10: Near-Side and Far-Side Stop Net Delay versus Red Ratio (r/C) for the Bus Phase for (a) 18 tdwell/C = 0.40 and for (b) tdwell/C = 0.60
20
1 Overall, far-side stop is superior to near-side stop with zero setback distance and yields
2 consistent results under all scenarios. If setback distance is considerably large, then the signals have no
3 effect on stop delay and near-side stop functions as would like a far-side stop.
4 Conclusion
5 The analyses show that the most significant benefit at an urban intersection could be obtained by
6 relocating a near-side stop with zero setback to a far-side location. If the bus stop is on a congested
7 approach with high r/C ratio, far-side stops may result in delay reductions of more than 30 seconds per
8 bus per intersection. Moreover, on a congested approach, pulling the stop 100 feet or further back away
9 from the intersection stop bar results in savings more than 20 seconds by preventing the traffic queue
10 from blocking the stop (i.e., limited queue interference). Far-side relocation savings become smaller as
11 dwell times increase since higher portion of the dwell time at a near-side stop overlaps with the red
12 signal.
13 Another important finding is with respect to the upper limit of travel time savings that could be
14 obtained via two-sided queue jump lanes. The results show that the highest savings with a queue jump
15 lane is approximately 9 seconds per bus per intersection. This assumes the most favorable design and
16 operating conditions (e.g., far-side stops, presence of a receiving lane and thus no required transit-only
17 phase, no right-turning vehicles in the queue jump lane, queue jump lane corresponding to 95th
18 percentile bus phase queue length, and high bus phase v/c ratio). As the amount of right-turns increase
19 along with the number of pedestrians to whom the right-turners need to yield, the savings get smaller.
20 For example, when the hourly pedestrian volume is more than 150 in conjunction with more than 100
21 right turning vehicles, the benefit of queue jump lane disappears. Similarly, the less congestion there is,
22 the smaller the savings.
21
1 TSP with far-side stop and 15 seconds of green extension and red truncation can offer up to 19
2 seconds of reduction in delay, where the benefits become more pronounced with high v/c ratio. Results
3 show that with low v/c ratio (e.g., 0.4), which may be the case for buses traveling on the main arterial at
4 major-minor intersections, granting 10 seconds of green extension without red truncation provides only
5 about 2 seconds delay reduction per intersection. Finally, the deterministic methods of estimating TSP
6 benefits, which assume uniform traffic arrivals, closely match the simulation results (root mean square
7 error is less than one second). Therefore, practitioners are also encouraged to use the deterministic
8 model to obtain planning-level estimates of savings that could be obtained through TSP.
9 Acknowledgments
10 The authors would like to thank Prof. Peter Furth of Northeastern University for his valuable comments
11 and suggestions to improve the quality of the paper.
22
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