Case Study 5 Museum Road Educational and Training Presentation Problem 2

2a. Fully actuated signal - Improved T intersection Problem 2 2a. Fully actuated signal - Improved T intersection - Minimum green times - Exclusive pedestrian phase 2b. Signalized analysis - Phasing options - Combining movements - Reduced cycle length 2c. Coordination effects - Arrival type - Unit extension and k-value - Delay (d1 and d2) Continuing our analysis of the Reitz Union Drive intersection, we will now look at some additional options under signal control. We can first analyze operations of the improved intersection with no northbound approach and two exclusive right-turn lanes southbound, using an actuated, two-phase signal with a 120-second cycle. Then, we can investigate improvements to this design to quantify their effects as input to choosing alternatives to potentially minimize congestion. Continuing to use future traffic projections and the improved geometric conditions suggested in Sub-Problem 1c, we can compute the delays and level of service at this signalized intersection, assuming that it is operating under fully-actuated control. As we work through these computations, we will be able to investigate several aspects of an actuated signal. We can first look at some options to test phasing alternatives to accommodate pedestrians. Such analyses will allow us to quantify the effects of these signal modifications toward resolving these issues using: - minimum green times to accommodate pedestrians - effects of introducing an exclusive pedestrian phase Next, we will consider an option to improve the phasing at this intersection by investigating its operation with existing phasing to identify: deficiencies in capacity and delay by movement phasing modifications to alleviate these movement deficiencies Finally, we can investigate semi-actuated control for potential coordination with adjacent signals and what effect it has on the overall operation in sub-problem 2c by looking at: unit extension and k-value versus arrival type and progression factor double cycle option to compare overall delay and level of service We will compare the overall operation of the signalized intersection operating with and without improved phasing and timing, as well as actuated versus semi-actuated control to better recommend alternative solutions. In Problem 2, we are looking at strategies to improve the intersection, mostly as an isolated signal with the addition of the traffic generated by the new parking structure, but we are introducing the idea of semi-actuated control for potential coordination with the adjacent intersections.

Overview of the Problem Fully actuated signal Lane configuration Volumes and PHFs Pedestrian flow rates Pedestrian crossing data Bicycle flow rates Queue spacing Queue storage Grades Heavy vehicles Parking data Bus stop data We can set up this analysis by using the data from Problem 1 to analyze the actuated signal control of the improved intersection with projected traffic in a standard HCM application using the procedures in Chapter 16 for signalized intersections. The operational analysis of a signalized intersection under actuated control requires the following typical data: peak-hour turning movement volumes and peak-hour factors pedestrian and bicycle flow rates pedestrian walking speed, travel distance, and crosswalk width lane numbers, widths, and usage queue spacing and storage signal phasing, timing, and clearance data number of approach grades, heavy vehicles, parking, and bus stop influence

Overview of the Problem (cont.) Critical data Traffic, geometry and signal phasing Same data from Problem 1 Two-phase, fully actuated signal operating at a 120-sec cycle length. The HCM requires static phase lengths for analysis purposes, even though an actuated signal will vary phase lengths cycle-to-cycle reacting to demand. We will see later how actuation is accounted for in the delay equation for actuated movements.

Overview of the Problem (cont.) Run Overview of the Problem (cont.) Initial Run Queues: Important to look at independently Delays: Important to look at all movements LOS: Overall intersection not the only LOS Using this data to work through the HCM procedures will yield for each movement and approach: capacity v/c ratio queue storage ratio delay level of service Results of our analysis, including overall intersection delay and level of service All delay and LOS values are important, not just for the overall intersection. As you can see, the intersection is operating at LOS D, but there is one movement (EB left) that has severe delay problems (219 sec/veh) Queue storage is also used to compare with the estimated back of queue. These values can be for storage lanes in the case of exclusive turning movements and distances between intersections in the case of thru movements. A "queue storage ratio" is computed by dividing the storage by the estimated back of queue in vehicles per lane. A queue storage ratio greater than 1.0 indicates that storage is not adequate to handle the estimated queues. Note: The capacity, delay and LOS results from the HCM procedures assume all lane groups have adequate storage and do not account for the effects of turning traffic spilling into adjacent lanes, or thru traffic spilling back to adjacent intersections.

Problem 2a: fully-actuated signal Pedestrian effects Minimum green times Crossing distance of 50 ft Crosswalk width of 10 ft Walking speed of 4 fps  Yields a minimum green of about 20 sec Assuming we need to maintain the 120-second cycle, we need to compute the pedestrian green time for the diagonal movement crossing. Using a crossing distance of 50 feet, a crosswalk width of 10 feet and a 4-feet-per-second walk speed, the minimum pedestrian time is calculated to be about 20 seconds. This assumes 500 pedestrians in thirty 120-second cycles per hour, or 17 per interval in HCM Equation 16-2

Problem 2a: fully-actuated signal Pedestrian effects Exclusive pedestrian phase Will pedestrians get more time than before? What are the benefits of an exclusive pedestrian phase? Because of the large number of pedestrians at this intersection, we might want to consider an exclusive pedestrian phase. We have resolved part of the pedestrian conflicts with vehicles by closing the northbound approach to vehicular traffic in Problem 1. However, the northeast movement of pedestrians from parking to classes suggests a diagonal crossing might be worth some consideration. Take a few minutes to review the phasing plan with the exclusive pedestrian phase. By moving the pedestrians to their own phase, will they be assigned more or less time than they were before? What benefits are derived by assigning pedestrians with an exclusive phase?

Problem 2a: fully-actuated signal Run Problem 2a: fully-actuated signal Pedestrian effects Exclusive pedestrian phase Pedestrians accommodated more efficiently and safely However, the intersection performance is compromised SB approach from LOS C to LOS E/F Intersection from LOS D to LOS E To evaluate the effects of this signal timing strategy, we will use the Chapter 16 HCM operational methodology. Running the analysis for a 120-second cycle results in the queues, delays, and LOS values While pedestrians are accommodated more efficiently and more safely, the intersection performance is worsened under this scenario, at least with respect to the LOS criterion. On the southbound approach, LOS drops from C to E/F. Since pedestrians are restricted to crossing only the northbound and westbound approaches (with the northbound approach closed to vehicles), the need for an exclusive pedestrian phase is probably minimal, especially with the deterioration of the intersection efficiency using this design.

Problem 2b: signalized analysis Signal phasing options EB left-turn movement critical SB right-turn movement critical Modify phasing to improve? Remember from our initial analysis of the Reitz Union Drive improvement strategy (see Exhibit 5-23) that the most urgent deficiency is the eastbound left-turn movement, with an estimated delay in excess of 200 seconds per vehicle. The first mitigating option that would be the easiest to implement and the least costly would be to simply modify the signal phasing. We can test if providing a signal phase to alleviate the saturated movements might reduce the delay on those movements, being cognizant of the effects on the overall intersection. Discussion: Take a few minutes to determine a phasing plan that would reduce the delay of the critical movements. Click continue when you are ready to proceed.

Problem 2b: signalized analysis Adding protection Combining movements Modifying cycle length More protected time to deficient movements Concurrent movements for efficiency Lower cycle and still accommodate needs Referring once again to the results of our initial analysis (see Exhibit 5-23), we see that there may be an opportunity to combine improvements through phasing design, since the two most deficient movements are the eastbound left and the southbound right. This allows us to introduce a phase that implements a leading protected left-turn phase eastbound that can run concurrently with a protected right-turn phase southbound This phasing provides more protected time to the most deficient movements to improve the overall efficiency of the intersection,

Problem 2b: signalized analysis Run Problem 2b: signalized analysis Let's compare the results of this analysis (Exhibit 5-25) with our initial assessment (Exhibit 5-23). The eastbound left delay went from 219 sec/veh to 21 sec/veh while maintaining reasonable performance levels for other movements. The westbound movements were slightly improved (LOS C to B) with some deterioration for southbound movements (LOS C to D/E). The overall intersection improved from a delay of 53 sec/veh (LOS D) to a delay of under 22 sec/veh (LOS C). These results suggest that the added phase offers an overall improvement to the operation of the intersection at a level that warrants its implementation.

Problem 2c: coordination effects Signal control options - Fully actuated - Semi-actuated - Coordination Analysis factors affected? Arrival type  Progression factor Unit extension  k-value The previous analyses assumed fully actuated signal control. With adjacent signalized intersections located close by, coordination would be desirable. This Sub-problem provides an opportunity to compare the effects of operating the Museum Road/Reitz Union Drive signal as fully actuated with the effects operating it under semi-actuated control. A constant cycle length can be maintained if the intersection is operated under semi-actuated control, thereby allowing coordination with the other signals along Museum Road. In an HCM analysis, the factors affected in this comparison are arrival type, progression factor, unit extension, and the k-value.

Problem 2c: coordination effects Arrival type 1 – Very poor progression 2 – Unfavorable progression 3 – Random arrivals 4 – Favorable progression 5 – Highly favorable progression 6 – Exceptional progression Progression factor – Accounts for effects of progression Unit extension – Minimum gap between successive vehicles k-value – Accounts for effects of actuation Arrival type consists of six assigned categories for determining the quality of progression at a signalized intersection. This parameter approximates the quality of progression as follows: Arrival Type 1 is characterized by a dense platoon of more than 80 percent of the lane group volume arriving at the start of the red phase. Arrival Type 2 is characterized by a moderately dense platoon that arrives in the middle of the red phase or by a dispersed platoon of 40 to 80 percent of the lane group volume arriving throughout the red phase. Arrival Type 3 consists of random arrivals in which the main platoon contains less than 40 percent of the lane group volume. Arrival Type 4 consists of a moderately dense platoon that arrives in the middle of a green phase or of a dispersed platoon of 40 to 80 percent of the lane group volume arriving throughout the green phase. Arrival Type 5 is characterized by a dense to moderately dense platoon of more than 80 percent of the lane group volume arriving at the start of the green phase. Arrival Type 6 is reserved for exceptional progression quality on routes with near-ideal characteristics. Progression adjustment factor is a factor used to account for the effect of signal progression on traffic flow. This parameter is denoted as the variable PF and is applied only to the uniform delay component of the equation for estimating control delay at a signalized intersection.   Unit extension is the minimum gap, in seconds, between successive vehicles moving on a traffic-actuated approach to a signalized intersection that will cause the signal controller to terminate the green display k-value

Problem 2c: coordination effects Progression effects on delay: Arrival type described level of progression Progression factor applied to uniform delay (d1) term Actuation effects on delay: Unit extension describes actuation activity k-value applied in the incremental delay (d2) equation Progression factor is 1.0 for fully actuated intersections  But actuation is accounted for in the k-value Progressed phases are not actuated (k-value = 0.5)  But progression accounted for in the progression factor The arrival type is 3 for all movements under fully actuated control to model random arrivals. This results in a progression factor (HCM Equation 16-10) of 1.00 for all approaches, which means the first term of the delay equation (HCM Equation 16-9) for uniform delay (d1) is not adjusted for coordination. Under fully actuated control, the HCM procedures account for how responsive an actuated movement reacts to traffic by using the unit extension. This value represents how long (in seconds) a detector must be vacant before the controller will end the phase ("gap out"). In the HCM, the unit extension is used to determine the k-value for use in the delay equation (for incremental delay, d2). So, while fully actuated control does not lower d1, it does lower d2. Conversely, under semi-actuated control, the reverse is true. Since the major street through movements must be pretimed to accommodate coordination, the arrival type can vary, based on the degree of coordination provided. Under most situations, arrival type 4 is used for normal coordinated systems. (Arrival type 5 could be used in especially well coordinated systems like for one-way streets). Using arrival type 4 for both the eastbound through movement and westbound through and right-turn movements in this case results in progression factors from HCM Exhibit 16-12, based on the green (g/c) ratios but always values less than 1.00 to account for improvements in delay to these movements created by the coordination provided. The progression factor modifies the effects of uniform delay, d1. However, under semi-actuated control, the unit extension value for the eastbound through movement and the westbound through and right-turn movements will be ignored since these movements are under pretimed operation, resulting in a k-value of 0.50. This will not lower the d2 value, so we have a trade-off between these two control strategies. Observations?

Problem 2c: coordination effects Run Problem 2c: coordination effects Comparing operations Fully actuated (but not progressed) Semi-actuated (with progression) Our task here will be to compare these results to see which combination provides the better overall efficiency. We can make two runs: one with all actuated movements, arrival types of 3 and unit extension values of 3.0 seconds, and the other with eastbound through movements and westbound through and right-turn movements coded as pretimed, using arrival type of 4, with the unit extension values to be ignored. The results of these two runs are presented in Exhibit 5-26 so that we can compare the affected approaches and the overall intersection operations As you can see, the unit extension creates k-values of less than 0.50, which lowers d2. But, arrival type values of 3 result in progression factors of 1.00, with no effect on d1. However, under semi-actuated control, the k-value stays at 0.50, not affecting d2, but the progression factor is lower which reduces the d1 term. Overall, we can see that the combined effects of semi-actuated control on the d2 term outweigh those of fully-actuated control on the d1 term.

Problem 2c: coordination effects Run Problem 2c: coordination effects Comparing cycle lengths 120-second cycle 60-second cycle One last option we might consider, since most of these runs have assumed a  120-second cycle, is to investigate the possibility of a shorter cycle. However, in order to maintain the ability to coordinate with the other signals along the arterial (which we are assuming to be running the 120-second cycle), we must confine ourselves to a 60-second cycle. This is because the cycle length we use at Museum/Reitz Union must maintain an integer relationship with the 120 second cycle that controls other intersections along Museum Road. As examples, therefore, it could be 30, 40, or 60 seconds in duration. However, we must be cognizant of pedestrian crossing time requirements, and this is likely to eliminate anything less than 60 seconds. Operating the Museum Road/Reitz Union Drive intersection on a 60-second cycle while the remainder of the system operates on a 120-second cycle is commonly referred to as a  double-cycle option; it has the potential to lower delay at our intersection of interest (because of the lower cycle length) while still maintaining the benefits of coordination with upstream signals. Comparing the results between the 120-second and 60-second cycles illustrates a couple of points. Lower cycle lengths generally result in shorter delays overall, even though capacities go down. Also, the queues are reduced substantially because the red time per phase is less, reducing the time available for queues to lengthen. This is a good strategy where storage lengths are limited, as is the situation in this particular case study. The overall intersection delay was reduced and queues lowered for every movement by between 10% and 50%. Another by-product of this strategy is that the large number of pedestrians will not need to wait as long before receiving a WALK indication.