Case Study 4 New York State Alternate Route 7 Problem 4

Analysis of the Alternate Route 7 Freeway Facility Problem 4 Analysis of the Alternate Route 7 Freeway Facility Sub-problem 4a - How should the Alternate Route 7 facility be divided up for an HCM operational analysis? Sub-problem 4b - What is the operational performance of Alternate Route 7 during the off peak period? Sub-problem 4c - What is the operational performance of Alternate Route 7 during the peak period?

Sub Problem 4a If the demand exceeds the capacity of a section for one 15-minute period, we need to continue the analysis for another time period in order for all of the demand to be served. The overall length of the facility is such that vehicles are normally able to travel from one end to the other within 15 minutes, so that all demand can be served during the study period. The facility should be long enough to contain any queues that form and to ensure that there are no traffic interactions with any upstream facility. Based on these factors, list the segments that you think should be analyzed

Sub Problem 4a

Off-Peak Operational Analysis of Alternate Route 7 Sub Problem 4b Off-Peak Operational Analysis of Alternate Route 7

Sub Problem 4b

Sub Problem 4b What can you learn about the performance of the facility from these data?

Also note that the demand/capacity ratio is near one for this segment. Sub Problem 4b There is no overall performance measure for the facility; see parts 3 and 4 of the HCM Each of the segments performs at level of service C or better, with the exception of segment 2, the weaving segment This is consistent with our analysis produced in Problem 2 indicating a problem in the performance of the weaving segment Also note that the demand/capacity ratio is near one for this segment. What is the implication of a demand/capacity ratio that is this high?

Points to make here that limit the applicability of these results. Sub Problem 4b When we examine Exhibit 4-70, which deals with ramp operations, we can see one of the results of the d/c ratio near one for the weaving segment (segment 02). The demands on the on- and off-ramps are not completely served during this time period. Points to make here that limit the applicability of these results. A limitation in the software used to implement the HCM did not allow entry of 2 lanes to the on-ramp. This produces an unreasonable result of ramp delay and queuing. If this limitation were not present and the results were as shown in Exhibit 4-70, the unserved demand during this time period would be transferred to the next 15-minute time period. The same caveat must be applied to the off-ramp results. This example does have a limitation (due to current software characteristics) that we need to keep in mind.

Peak Operational Analysis of Alternate Route 7 Sub Problem 4c Peak Operational Analysis of Alternate Route 7 What happens on the freeway mainline when the demand during one time period exceeds the capacity of the freeway to handle the demand.

What are the key points from the results in time period 1? Sub Problem 4c What are the key points from the results in time period 1? What parameters are important in evaluating the operation of the freeway system?

The conditions on the freeway system are undersaturated Sub Problem 4c The conditions on the freeway system are undersaturated The forecasted LOS is C or above for all segments Speeds remain high, above 50 mph There is no queuing present The system operates well

What is the most important information you learn from this table? Sub Problem 4c What differences do you see between these results and those from time period 1? What is the most important information you learn from this table?

Sub Problem 4c There is a bottleneck in section 6, a point along the freeway facility that limits or constrains the demand, where the volume/capacity ratio equals 1.0. What is the cause of this constraint? It is where the mainline drops from three lanes to two lanes Here, the demand exceeds the capacity of the two lane section and a queue begins to build, traveling upstream from this location At the end of this 15-minute period (time period 2), the queue extends the entire length of section 5 (1,890 feet) It also reaches section 4 nine minutes after the beginning of time period 2 and extends 745 feet through this section by the end of the 15-minute time period Both sections operate at level of service F, even though the demand/capacity ratios for these sections are well below 1.0 These sections are in the congested regions of the speed/flow diagram as shown by the very low speeds (below 30 mph) that exist in these sections

For the sections downstream from the bottleneck (section 6) Sub Problem 4c For the sections downstream from the bottleneck (section 6) The volume/capacity ratio is less than the demand/capacity ratio. Some vehicles that desire to reach sections downstream from the bottleneck (sections 7 through 11) are unable to do so during time period 2. They are in the queue forming in sections 4 and 5 and will be delayed in this queue until at least time period 3. This unserved demand is transferred from time period 2 to time period 3.

The speed in segment 5 is less than 20 mph during this recovery Sub Problem 4c The queue formed during time period 2 clears during time period 3, by the first minute in segment 3 and by the third minute in segment 5 The demand that wasn't served during time period 2 has been transferred to time period 3, since the volumes in segments 4 through 11 that actually use the facility exceed the original demand for these segments During time period 3, all segments operate at level of service C or better, with the exception of segment 5, which is still recovering from the queue, and operates at level of service E The speed in segment 5 is less than 20 mph during this recovery

All segments of the freeway facility are operating at LOS B or better Sub Problem 4c All segments of the freeway facility are operating at LOS B or better All speeds exceed 40 mi/hr The demand equals the volume, indicating that all vehicles desiring to travel along the facility during time period 4 are served

Even in time period 1, when there is no queuing, there is delay. Problem 4 analysis Even in time period 1, when there is no queuing, there is delay. The average mainline speed is less than 55 mph (54.42 mph), so there is some, though minimal, delay. The delay increases during time period 2 to nearly 1.5 minutes per vehicle, and the average speed drops to 44.15 mph. These system measures do provide a broad perspective on the performance of the freeway facility and are therefore valuable aids to analysts and decision makers. However, to understand the specific causes of delay or queuing, we must always look at the details of the facility performance, checking the data for each section to understand the causes of poor performance. What are the implications of these results?

Have we considered a wide enough view of the system? Problem 4 discussion We found the facility performs well during the off peak, but the lane drop from three to two lanes on the eastbound portion of the facility results in some delay for motorists during the PM peak period. We also need to consider whether further analyses should be conducted to have a complete picture of the operation of this facility. Let's consider the following issues: Have we considered a wide enough view of the system? Are there limitations of the HCM methodology that require us to use other tools, such as simulation?

Have we considered a wide enough view of the system? Problem 4 discussion Have we considered a wide enough view of the system? Widening the system to include the interchanges might prove beneficial in our assessment of Alternate Route 7 since the interchanges themselves affect the operation of the system Are there limitations of the HCM methodology that require us to use other tools, such as simulation? Since demand exceeds capacity, particularly when there is an intersection of queues on the facility, a micro-simulation model to follow the behavior of individual vehicles and drivers as they negotiate a congested facility We are considering a large and complex system, such as a freeway mainline and interchanges