HCM 6th Edition: Urban Street Facilities

HCM 6th Edition: Urban Street Facilities
Today’s web briefing is focused on the urban street facilities evaluation methods that are in Chapters 16 and 17 of the newly released HCM 6th Edition.

Instructor [Note: Instructor should show their name, title, affiliation, and HCM-related background. If the presentation is via webinar, then add a photo of instructor] My name is: _______________. I will be the instructor for today’s presentation. I am a _______________ with ____________.

Overview and Background
Session 1 Overview and Background Briefing series overview Objectives and scope of briefing Note: “HCM” → Highway Capacity Manual Content and Structure of HCM Methodology Basics New Capabilities This briefing is organized into four sessions. The first session is intended to provide some context for our examination of the Urban Streets Facilities chapter. In this session, I plan to review the schedule for this briefing series and then outline the objectives of this presentation. The second session will identify the content and structure of the HCM 6th Edition, as it relates to the urban street facilities chapter. The third session will provide an overview of the methodologies in this chapter and highlight some of the new terms and concepts that are used. The last session will highlight some of the new evaluation capabilities of the methodologies.

Briefing Series Overview
What’s New – HCM 6th Edition New Features in Freeway Analysis Chapter Freeway Reliability and Strategy Assessment Urban Street Segments Urban Street Facilities Signalized Intersections Signalized Intersection Planning Application Roundabouts Ramp Terminals and Alternative Intersections Planning and Preliminary Engineering Guide Today’s briefing is being offered as one in a series of ten briefings on the HCM 6th Edition. This briefing on Urban Street Facilities is the fifth in this series.

Objectives and Scope Learning Objectives Scope of Presentation Focus
Learn about new capabilities of the urban street facilities chapter Understand how the chapter can be used to evaluate urban street facility operation Scope of Presentation HCM 6th Edition Urban Street Facilities chapters Focus Changes since publication of HCM 2010 There are two objectives for today’s discussion. One objective is to help you learn about the new capabilities of the Urban Street Facilities chapter. A second objective is to help you understand how the chapter can be used to evaluate urban street operation. Our discussion centers on the methodologies in the Urban Street Facilities chapter of the HCM 6th Edition. These methodologies are used to evaluate urban street segment operation. There is one methodology for evaluating the motorized vehicle travel mode, one for evaluating the pedestrian mode, one for the bicycle mode, and one for the transit mode. Given the limited time that we have for this presentation, we will need to focus our discussion on a few key topics. To this end, I am planning to focus on the changes made to the methodologies since their publication in HCM 2010.

Presentation Overview
Session 1 – Overview and Background Session 2 – Content and Structure Session 3 – Methodology Basics Session 4 – New Capabilities We are now ready to transition to Session 2. In this session, we will discuss the content and structure of the HCM 6th Edition, as it relates to urban street facilities.

Session 2 Content and Structure HCM organization Chapter titles
Chapter outlines For this session, I will show you the organization of the HCM and describe how it will be changed for the soon-to-be-published HCM 6th Edition. My approach will be to list the HCM chapters related to urban street facilities, describe the changes to the chapter titles, and summarize the changes being made to chapter contents. Let’s get started...

Volume 2 – Uninterrupted Flow Volume 3 – Interrupted Flow
HCM Organization Volume 1 - Concepts Volume 2 – Uninterrupted Flow Volume 3 – Interrupted Flow Volume 4 – Applications Guide The HCM consists of four volumes. They are shown here. No changes to volume titles will be made for the HCM 6th Edition. The first three volumes are included in the printed copy of the manual. The fourth volume is available from the Internet at the address shown. The chapters we will be discussing today are located in Volumes 3 and 4. Let’s take a closer look at them...

Chapters HCM 2010 HCM 6th Edition Volume 3 Volume 4 Volume 3 Volume 4
16: Urban Street Facilities (USF) Volume 4 29: USF Supplemental HCM 6th Edition Volume 3 16: Urban Street Facilities 17: Urban Street Reliability and ATDM Volume 4 29: USF Supplemental Note: “ATDM” → active traffic and demand management The urban street facilities information is currently located in Chapters 16 and 29. Chapter 16 is located in Volume 3, and Chapter 29 is located in Volume 4. For the HCM 6th Edition, the chapter titles and numbers remain the same. However, a new Chapter 17 has been added. The new chapter addresses two topics. One topic describes in detail how the HCM can be used to evaluate urban street reliability. The second topic describes a conceptual approach for evaluating alternative ATDM strategies. Ok, now let’s take a look at the section titles in each chapter...

Volume 3 Chapter Outline
HCM 2010 Chapter 16 Introduction LOS criteria Input data Methodology Auto methodology Pedestrian method. Bicycle methodology Transit methodology Applications Example Problems HCM 6th Edition Chapter 16 Introduction Concepts LOS criteria Motorized Vehicle Method. Input data Pedestrian Methodology Bicycle Methodology Transit Methodology Applications All of the chapters in Volume 3 have been reorganized slightly for the HCM 6th Edition. Most notable is that each of the methodologies in a chapter will be assigned its own separate section in the HCM 6th Edition. This approach concentrates all of the information needed to apply a specific methodology into one section. For urban street facilities, the new Chapter 16 will have four “methodology” sections. There is one section describing the methodology for evaluating the motorized vehicle travel mode, one section for the pedestrian mode, one for the bicycle mode, and one for the transit mode. I should also note that the example problems have been moved from Chapter 16 to Chapter 29, which is in Volume 4.

HCM 2010 Did not exist HCM 6th Edition Chapter 17 Introduction Concepts Objectives for reliability analysis Core Methodology Input data Extensions to Methodology ATDM strategy evaluation Applications Note: chapter addresses only the motorized vehicle mode The content of Chapter 17 will be entirely new for the HCM 6th Edition. Following the format of Chapter 16, the new Chapter 17 will have a Introduction, Concepts, Methodology, and Applications sections. The content of these sections will be focused on the use of the urban streets facility methodology to evaluate travel time reliability. The section titled “Extensions to the Methodology” introduces the concept of urban street ATDM and describes a conceptual approach for evaluating alternative ATDM strategies using the HCM. The approach is considered “conceptual” because is merely a framework that outlines how the HCM should be used to evaluate a few key strategies. A formal methodology is not yet provided for ATDM strategy evaluation. However, we expect that this methodology will be developed and published in a future edition of the HSM. I should note that Chapter 17 is focused on the evaluation of the motorized vehicle mode. It does not include information specific to the evaluation of service provided to pedestrians, bicycles, or transit riders.

HCM 2010 Chapter 29 Introduction Use of Alternative Tools HCM 6th Edition Chapter 29 Introduction Scenario Generation Sustained Spillback Use of Alternative Tools Example Problems Chapter 29 has been expanded for the HCM 6th Edition. Specifically, some of the details of the reliability methodology have been added to the chapter. Notably, there is a new section in Chapter 29 that describes the procedure for generating the evaluation scenarios needed for a reliability evaluation. There is also a new section that describes a procedure for extending the methodology in Chapter 16 to the evaluation of urban street facilities that experience spillback on one or more segments.

Questions on Content or Structure?
Content and Structure HCM organization Chapter titles Chapter outlines Questions on Content or Structure? This concludes the session on Content and Structure of the HCM. Let’s take a few minutes to answer some questions.

Session 1 – Overview and Background Session 2 – Content and Structure Session 3 – Methodology Basics Session 4 – New Capabilities OK, let’s continue with Session 3 - Methodology Basics

Session 3 Methodology Basics Calculation framework New input data Note
Focus of this session is on Chapter 16: Urban Street Facilities Urban street reliability methodology in Chapter 17 is discussed in Session 4 For this session, we will review the sequence of calculations represented by the methodology, and then we will discuss the new types of input data that are needed to use the methodology. The focus of discussion in this session is on the methodology in Chapter 16. The reliability methodology in the new Chapter 17 will be discussed later, in Session 4.

Calculation Framework
Motorized Vehicle Methodology Determine base free-flow speed Determine travel speed Determine spatial stop rate Determine level of service The methodology for evaluating the motorized vehicle mode on an urban street facility consists of four calculation steps. They are completed in sequence (from top to bottom) for a complete evaluation. They are... [read] Application of this methodology is based on the analyst’s application of the Urban Street Segments methodology to each segment on the facility. Once the segment results are available, the methodology in Chapter 16 describes how to combine the segment results to produce facility-wide results. I should note that the sequence of steps has not changed for the HCM 6th Edition.

Pedestrian Methodology Determine pedestrian space Determine pedestrian travel speed Determine pedestrian LOS score Determine pedestrian LOS The methodology for evaluating the service provided to pedestrians on an urban street facility consists of four calculation steps. They are completed in sequence (from top to bottom) for a complete evaluation. They are... [read] Similar to the motorized vehicle methodology, application of the pedestrian methodology is based on the analyst’s application of the Urban Street Segments methodology to each segment on the facility. Once the segment results are available, the methodology in Chapter 16 describes how to combine the segment results to produce facility-wide results. I should note that the sequence of steps has not changed for the HCM 6th Edition.

Bicycle Methodology Determine bicycle travel speed Determine bicycle LOS score Determine bicycle LOS The methodology for evaluating the service provided to bicyclists on an urban street facility consists of three calculation steps. They are completed in sequence (from top to bottom) for a complete evaluation. They are... [read] Similar to the motorized vehicle and pedestrian methodologies, application of the bicycle methodology is based on the analyst’s application of the Urban Street Segments methodology to each segment on the facility. The methodology in Chapter 16 is then used to combine the segment results to produce facility-wide results. I should note that the sequence of steps has not changed for the HCM 6th Edition.

Transit Methodology Determine transit travel speed Determine transit LOS score Determine transit LOS The methodology for evaluating the service provided to transit riders on an urban street facility consists of three calculation steps. They are completed in sequence (from top to bottom) for a complete evaluation. They are... [read] Similar to the other methodologies, application of the transit methodology is based on the analyst’s application of the Urban Street Segments methodology. The methodology in Chapter 16 is then used to combine the segment results to produce facility-wide results. I should note that the sequence of steps has not changed for the HCM 6th Edition.

Motorized Vehicle Methodology Pedestrian Methodology
New Input Data Motorized Vehicle Methodology No new input data Pedestrian Methodology Bicycle Methodology Transit Methodology Good news! There are no new input data needed for the methodologies described in Chapter 16.

Questions on Methodology Basics?
Calculation framework New input data Questions on Methodology Basics? This concludes the session on Methodology Basics. Let’s take a few minutes to answer some questions.

Session 1 – Overview and Background Session 2 – Content and Structure Session 3 – Methodology Basics Session 4 – New Capabilities OK, let’s continue with Session 4 - New Capabilities

Session 4 New Capabilities Motorized Vehicle Methodology
Chapter 16: Urban Street Facilities Sustained segment spillback Level of service Chapter 17: Urban Street Reliability and ATDM Travel time reliability Example application of reliability evaluation ATDM strategy evaluation Pedestrian and Bicycle Methodologies For this session, we will briefly look at the procedures that were added, or underwent major revision, for the HCM 6th Edition. For the motorized vehicle methodology in Chapter 16, a segment spillback procedure was added so the methodology could be used to evaluated congested street systems. Also, the process for determining level of service has been revised slightly. As mentioned in a previous slide, Chapter 17 is entirely new. It describes a process for using the urban streets facility methodology to evaluate travel time reliability. I have a few slides that demonstrate an application of the reliability evaluation process. Chapter 17 also introduces the concept of urban street ATDM and describes a conceptual approach for evaluating alternative ATDM strategies using the HCM. For the pedestrian and bicycle methodologies, the level-of-service thresholds were adjusted slightly to make them consistent with the thresholds used when the models were originally calibrated. Apparently, the thresholds used in HCM 2010 were incorrectly reported. We will take a look at all of these changes in the next few slides.

Motorized Vehicle Methodology
Sustained Segment Spillback Goals Reduce saturation flow rate of movements entering a segment that is full of queued vehicles Ensure segment delay reflects only vehicles that can queue on segment A new procedure for modeling the effects of sustained spillback is introduced in the HCM 6th Edition. Spillback occurs when more vehicles enter the segment than can be served at the downstream intersection thereby creating a queue from the downstream intersection that extends back to the intersection of interest. “Sustained” spillback is spillback that continues for multiple, successive signal cycles. The new procedure considers each of the movements entering the segment at the upstream intersection. It checks the downstream segment queue condition and, if the queue has spilled back, the procedure reduces the saturation flow rate of the movements entering the segment. The flow is reduced so that the capacity of the movements entering the segment matches the capacity of the movements exiting the segment at the downstream intersection. The procedure also adjusts the delay estimate for each movement experiencing spillback. The adjustment ensures that the predicted delay reflects only those vehicles that can queue on the segment. This approach prevents the delay estimate from including delay incurred by fictitious vehicles.

Level of Service LOS threshold values based on travel speed Values vary with base free-flow speed (BFFS) A > 80% of BFFS (e.g., 32 mi/h = 0.8 × 40), B > 67%, C > 50%, D > 40%, E > 30% LOS A threshold is 80% of BFFS (85% in 2010) The service measure is changed with the HCM 6th Edition. In HCM 2010, the service measure was “travel speed expressed as a percentage of base free-flow speed”. For the HCM 6th Edition, the service measure is just “travel speed.” The table shown here lists the threshold values of travel speed for each level of service. You can see that the threshold values vary by base free-flow speed. That is, each table column lists a set of threshold values for a given base free-flow speed. For example, a segment with a base free-flow speed of 40 mi/h has a threshold value of 32 mi/h for level of service A (as shown by the red oval). If you check, you will find that the threshold values used are a fixed percentage of the base free-flow speed. The same percentages are used for each column. As a result, the threshold values still vary by base free-flow speed. For example, the LOS A threshold for a 40 mi/h base free-flow speed is computed as 0.8 times 40, which equals 32 mi/h, as shown in the table and highlighted by a red circle. In fact, the LOS A threshold for any of the columns is 0.8 times the base free-flow speed. You can also check and find that the LOS B thresholds equal 0.67 times the base free-flow speed. Similarly, the LOS C thresholds equal 0.50 times the base free-flow speed. LOS D thresholds equal 0.40 times the base free-flow speed, and LOS E thresholds equal 0.30 times the base free-flow speed. As I previously noted, the LOS A threshold for the HCM 6th Edition is 80% of the base free-flow speed. In HCM 2010, the LOS A threshold was 85%. It has been reduced to 80% for the HCM 6th Edition to better reflect the real-world distribution of service levels among urban street segments.

Travel Time Reliability Goal Use HCM methodologies to evaluate effect of non-recurrent congestion events on urban street travel time reliability Calculation framework Scenario generation Facility evaluation Performance summary Chapter 17 describes a process for using the urban streets facility methodology to evaluate the effect of non-recurrent congestion-causing events on travel time reliability. The congestion-causing events that are addressed include: incidents, work zone presence, demand fluctuations, special events, and weather. The evaluation process is described in terms of a framework of calculations. These calculations are completed in succession. First, there is a scenario generation stage. Then, the scenarios are evaluated. Finally, the evaluation results are used to summarize facility performance. Let’s take a closer look at the calculation framework, but before we do I want to define some terms...

Reliability Terminology Analysis period Time interval evaluated by one application of the HCM Study period Time interval evaluated within a day (e.g., 7 to 10 am) Equals 1 or more analysis periods Reliability reporting period Time represented by reliability evaluation (e.g., 1 year) Scenario A scenario is a unique combination of traffic demand, road geometry, capacity and traffic control conditions, as may be influenced by incident and weather events The discussion of reliability evaluation includes some new terms. So, we need to go over these terms first before we get any further into the discussion of reliability. There are four terms listed on this slide. The first term is “analysis period”. Of the four terms, it is the only one that is not new. It is a term used throughout the HCM. It is defined as ... [read]. The typical analysis period for an HCM evaluation is 15 minutes in duration. The second term is “study period”. It is defined as ... [read] So, if the study period is from 7:00 am to 10:00 am, then it consists of 12 analysis periods. That is, the first analysis period is from 7:00 to 7:15, the second period is from 7:15 to 7:30, the third period is from 7:30 to 7:45, and so on. The third term is “reliability reporting period”. It is defined as ... [read] The fourth term is “scenario”. [read] For urban street evaluations, each scenario has a duration that is equals one analysis period. So, if the reliability reporting period is 1 year long, and the study period is 3 hours long (say from 7:00 am to 10:00 am each day of the year), and the analysis period is 15 minutes long, then you can see that there will be several thousand unique scenarios that must be generated.

Framework Scenario generation Demand variability Supply variability Strategies Facility evaluation HCM methodology Performance summary Travel time distribution Reliability metrics Some more details about the calculation framework are shown here. The scenario generation stage creates a series of scenarios that describe demand variation, capacity variation, and possibly, the effect of various traffic management strategies on operation, as they occur during the reliability reporting period. Once the scenarios are generated, they are evaluated using the HCM Urban Street Facility methodology. Finally, the results from the evaluation are used to develop the travel time distribution. This distribution is then used to summarize facility performance using various reliability metrics. We will take a look at these metrics (or measures) in a later slide.

Scenario Generation Weather event procedure Traffic demand variation procedure Traffic incident procedure Scenario generation procedure The scenario generation stage of the reliability evaluation process consists of four procedures. These procedures are completed in sequence to produce the desired set of scenarios for a given reliability reporting period. The four procedures are listed here. [read]. They are described in more detail in the next few slides.

Weather Event Procedure Predict weather for each scenario Weather event types considered Clear, dry pavement Rainfall, wet pavement (including intensity) Clear, wet pavement Snowfall, snow on pavement (including intensity) Clear, snow on pavement Reporting period weather event prediction Based on input average weather data for each month Default monthly weather data available for 284 cities Monthly, daily, and hourly event prediction Based on Monte Carlo method to add random variation in weather event time, type, and duration The weather event procedure is used to predict the weather conditions associated with each scenario. The weather event types considered include: [read]. The procedure predicts weather events based on monthly average weather statistics for the city or region of interest. These statistics include: total precipitation, total snowfall, precipitation rate, and so on. Default weather statistics, based on 10-year averages, are available for 284 cities. Several websites are identified as having the desired weather input data. Weather events have an important impact on traffic operation and travel time. The variable occurrence, intensity, and duration of these events has an impact on travel time variability, which feeds into travel time distribution. A Monte Carlo method is used to replicate the random occurrence of weather events during the reliability reporting period (which is typically one year in duration). Specifically, a random number generator is used to determine whether it rains on a given day, and if it does rain, during what time period and with what rainfall intensity.

Traffic Demand Variation Procedure Predict demand for each scenario Monthly, daily, hourly volume prediction Based on input average volume data Input data can be based on trends from nearest similar urban street with continuous count station Default volumes provided for arterials and collectors Analysis period volume prediction (within hour) Based on Monte Carlo method to add random volume variation The traffic demand variation procedure is used to predict the traffic demand associated with each scenario. The weather event types considered include: [read]. The procedure predicts traffic demand based on average traffic volume variation by month-of-year, day of week, and hour of day. These averages are input values. They can be obtained from the nearest street that has a continuous traffic count recording station. Default values are provided in Chapter 17. A Monte Carlo method is used to replicate the random variation of traffic demand with each one-hour period. Specifically, an input peak hour factor and a random number generator is used to determine the volume associated with the four 15-minute scenarios that occurs during each one-hour period of interest.

Traffic Incident Procedure Predict incidents for each scenario Incident types considered Segment, intersection Crash, non-crash Shoulder, one-lane closed, two or more lanes closed Fatal-or-injury crash, property-damage-only, breakdown, other Reporting period incident event prediction Based on input average incident data Default incident probability distribution provided Hourly incident event prediction Based on Monte Carlo method used to add random variation to incident location and duration The traffic incident procedure is used to predict the incident events associated with each scenario. The incident types considered include: [read]. The procedure predicts incident events based on an incident probability distribution that considers incident type, location, and severity. A default distribution is provided, if local data are not available. A Monte Carlo method is used to replicate the random occurrence of incidents during the reliability reporting period. Specifically, a random number generator is used to determine whether an incident occurs on a given day, and if it does occur, during what time period and whether it is a severe crash closing one lane, or a breakdown on the shoulder.

Scenario Generation Procedure Work day-by-day, analysis-period-by-analysis-period in chronologic order through the year to predict... If weather present... Adjust free-flow speed Adjust saturation flow rate Adjust critical left-turn headway Volume If incident present at specific location... Adjust speed Reduce number of lanes on segment The scenario generation stage uses the three aforementioned procedures (i.e., weather, demand, and incident) to define the conditions present for each scenario of the reporting period. Each scenario is generated in a chronologic manner. It starts with the first analysis period to occur at the start of the study period during the first day of the reporting period. For this scenario, the weather conditions are predicted first. If there is rain or snow, then the free-flow speed, saturation flow rate, and critical left-turn headway are adjusted accordingly. Then, the volume is adjusted to account for the month-of-year, day-of-week, and hour-of-day variation. Finally, a check is made to determine whether an incident occurs. The probability of an incident is influenced by the weather conditions present and the demand volume level. If an incident occurs, then the saturation flow rate is reduced, the running speed is reduced, and one or more lanes may be closed for the duration of the incident.

Reliability Performance Measures Based on travel time distribution Travel time index (TTI) Actual travel time divided by travel time at base free-flow speed Planning time index (PTI) 95th percentile highest travel time divided by base free-flow speed Reliability rating Percentage of vehicle-miles traveled by vehicles with a TTI less than 2.50 (i.e., LOS D or better) There are a variety of performance measures that can be used to describe reliability. Some of these measures are listed in this slide. All of them are based on the travel time distribution. The travel time index is one commonly used indicator of reliability. It represents the actual travel time divided by the travel time at the base free-flow speed. In this manner, a TTI of 1.0 indicates that the actual travel time equals travel time at the base free-flow speed. So, a TTI of 1.0 indicates a very reliable facility. Values larger than 1.0 indicate a less reliable facility. They indicate that the actual travel speed is slower than the base free-flow speed. If the 95th percentile travel time is divided by the travel time at the base free-flow speed, the result is a special type of TTI called the planning time index, or PTI. This measure is useful for indicating the near-worst-case conditions that are present on a facility. The reliability rating represents the [read]. This measure combines the TTI and the vehicle-miles traveled on a facility. It indicates the percentage of VMT that has a level of service of D or better.

Reliability Performance Measures Planning time index Planning Time This slide shows a typical travel time distribution for a facility that is about three-fourths mile long. The base free-flow speed is 41 mi/h, which equates to a travel time of 60 s. The 95th percentile travel time is 173 s. So, the PTI is 2.9 (= 173/60) The extremely large travel times (on the right side of the figure) are due primarily to incidents. Those travel times in the range of 120 to 150 s are often due to fowl weather conditions. Travel Time, s

Dealing with Random Variation A “complete period evaluation” (CPE) represents Results for all scenarios in one reliability reporting period One possible combination of volume, weather, and incidents Monte-Carlo method Produces a slightly different result for each CPE if random number seed is changed for each CPE As we discussed previously, there are a wide variety of weather events and a large number of incident types. There are also a large number of volume levels during the course of a given year. We could try to list all possible combinations of weather, incidents, and volume using a decision tree, however, the number of possible branches is very, very large. In addition, the random nature of weather events and incidents makes it difficult to determine the probability of occurrence for each branch of the decision tree. We could “prune” off some of the branches, leaving only the more likely combinations. But, doing so would also eliminate some of the variability that is fundamental to understanding reliability. Therefore, the Monte-Carlo method is the best means to deal with the random variability of weather events, incidents, and volumes. It also allows us to avoid the construction of a complicated decision tree. Before going further, lets define a “complete period evaluation”, or CPE. A CPE represents the collective set of evaluation results for all scenarios in one reliability reporting period. For example, a CPE might represent the results for the 7:00 to 10:00 am study period for January 1, 2014 to December 31, 2014. However, we know that the combinations of weather, incidents, and traffic vary from year to year. The weather and incidents in 2014 are not the same as those in 2013, 2012, 2011, and so on largely because of the randomness of weather, incidents, and traffic volume. This year-to-year variability is replicated using the Monte-Carlo method. By changing the random number seed, we can create a plausible travel time distribution for each CPE. For design, we need the “long-run average” as the basis for our decisions. So, using the reliability method, we replicate the evaluation using one unique random number seed for a set of CPE’s. Then we average the results to get the desired long-run average. This same approach is used in microscopic traffic simulation models (like VISSIM). The Monte-Carlo method is used to develop

Dealing with Random Variation Confidence interval Defines the range in which true travel time lies Process Multiple CPEs are performed, each with different seed Predicted travel time from each CPE used to quantify the standard error se CI computed for 95th percentile based on se As number of CPEs increases... Confidence interval gets smaller Analyst is more certain Results form a better basis for decisions For a reliability evaluation, we are typically interested in key statistics that describe the travel time distribution. These statistics include the average travel time, the median travel time, the 95th percentile travel time, and so on. When we have the travel time distribution from multiple CPEs, we can describe the desired distribution statistics using confidence intervals. A confidence interval defines the range in which the true travel time lies, with a specified level of statistical confidence. The process for computing this interval consists of three steps: First, evaluate the facility using multiple CPEs. Second, obtain the predicted travel time statistic (e.g., median travel time) from each CPE and use them to compute a standard error Third, use the standard error to compute the 95th percentile confidence interval An equation for computing this interval is provided in Chapter 17 (equation 17-3). This equation indicates that the confidence interval will be smaller if we increase the number of CPEs that we evaluate. Thus, we become more confident in our results when they are based on a larger sample.

Example Application 3-mile facility (6 segments); 35 mi/h speed limit Cycle length: 100 s; good two-way progression Analysis period: 15 min Study period: 7 to 10 am Reliability reporting period: Jan. 1 to Dec. 31 (excl. Sat. & Sun.) 3120 scenarios (=4 scen/h x 3 h/d x 5 d/wk x 52 wk/yr) The next few slides are provided to illustrate the reliability methodology using an example application. The facility of interest is 3 miles in length and consists of six segments, with each segment is 0.5 miles in length. The first two segments are show in plan view at the bottom of the slide. The rest of the segments are identical. The details of the facility are listed in this slide. [read]. The reliability reporting period extends from January 1 to December 31, excluding weekend days. The study period is three hours in length and the analysis period is 15 minutes. Based on these conditions, there are 3,120 scenarios in the reliability reporting period.

Example Application Results 95th % confidence interval calculation for 5 CPEs se = standard deviation / 5 ; t95 = 2.8 (Student t, 4) 95th % CI for average travel time: 432 to 444 s Travel Time, s CPE No. Average Median 95th % 1 444 372 784 2 441 787 3 433 371 758 4 439 740 5 434 773 438 768 Stand. Dev. 4.8 0.4 19.6 Stand. Error 2.1 0.2 8.8 Five complete period evaluations were conducted. Selected travel time statistics are shown for each CPE. The five travel times in column 2 of the table correspond to the average travel time. These five values are shown to vary because of random differences in weather, incidents, and traffic volume that occurred (I should remind everyone that the mean values upon which the Monte Carlo methods are based did NOT vary– they were the same for each CPE). The standard error is shown in the last row of the table. Using the equation in Chapter 17, the 95th percentile confidence interval for the Average travel time in column 2 is computed as 432 to 444 s. The best estimate of the true average travel time is 438 s, as shown in column 2, third row up from the bottom. _____________________________ Calculations for speaker reference: t_95 of 2.8 is based on the Student t distribution with four degrees of freedom (4 = 5 – 1). For average travel time: s_e = 4.8/sqrt(5) = 2.1 Upper limit of 95th percentile confidence interval is computed as: CI_95 = average TT + t_p x s_e 444.1 = x 2.1 Confidence interval for the median and 95th percentile values is computed in a similar manner.

Example Application - Alternatives Analysis Alternative 1 Reduce cross street left-turn phase split by 5 s Indirectly gives 5 seconds to coordinated phase Alternative 2 Major-street lefts: change prot-only to prot-perm Increases intersection crash frequency by 11 % Alternative 3 Increase major-street left-turn lanes from 1 to 2 Decrease major-street right-turn lanes from 1 to 0 Increases intersection crash frequency by 9 % Loss of right-turn lanes shifts some incidents to through lanes 5 CPEs for base, 5 CPEs for each alternative Now, let’s extend the example application to an alternatives analysis. In this case, we will use a reliability evaluation to assess three alternatives. The 3-mile facility described in the previous slides will be used for this alternatives analysis. It will represent the “base” condition. The three alternatives are [read]. As indicated in the last bullet, the results from the previous slide represent the base condition. Five complete evaluation periods were also prepared for each alternative. The results are shown in the next few slides.

Alternative 1 Reduce cross street left-turn phase split by 5 s Findings Alternative reduces average and 95th % travel time Small reduction in total delay Case Travel Time, s Total Delay, veh-h Reliability Rating Average 95th % Base 438 768 71 93.2 Alternative 401 542 66 96.8 Change -37 -226 -5 3.6 Significant? Yes For alternative 1, the change in phase splits resulted in a reduction in average travel time and a reduction in the 95th percentile travel time. There was a small reduction in total delay. There was a small increase in the reliability rating. All changes represent improved operations and improved reliability.

Alternative 2 Major-street lefts: change prot-only to prot-perm Findings Alternative reduces average and 95th % travel time Notable decrease in total delay Case Travel Time, s Total Delay, veh-h Reliability Rating Average 95th % Base 438 768 71 93.2 Alternative 383 473 49 97.3 Change -55 -295 -21 4.1 Significant? Yes For alternative 2, the change in left-turn operation resulted in a larger reduction in average travel time and the 95th percentile travel time. There was also a large reduction in total delay and a small increase in the reliability rating. All changes represent improved operations and improved reliability.

Alternative 3 Increase major-street left-turn lanes from 1 to 2 Decrease major-street right-turn lanes from 1 to 0 Findings Alternative reduces 95th % travel time and reliability rating (i.e., improves reliability) Case Travel Time, s Total Delay, veh-h Reliability Rating Average 95th % Base 438 768 71 93.2 Alternative 410 460 59 98.5 Change -28 -308 -12 5.3 Significant? No Yes For alternative 3, the changes to lane assignment resulted in a small reduction in average travel time but a large reduction in 95th percentile travel time. There was only a small reduction in total delay, but a notable increase in the reliability rating. All changes represent improved operations and improved reliability.

Example Application - Summary of Findings Alternative 2 - Change protected-only to protected-permitted Lowest average travel time Lowest total delay Lowest road user cost from delay perspective Alternative 3 – Add 1 left-turn lane, eliminate right-turn lane Lowest 95th % travel time Highest reliability rating Most reliable operation To summarize... [read]. It is worth noting here that the alternative producing the lowest road user cost from a delay perspective does not also produce the most reliable operation. This trend may not always occur, the alternative producing the lowest road-user delay cost may also produce the most reliable operation. However, this example does point out that delay and reliability are not surrogates. Each measure quantifies a different aspect of facility performance and both should be considered when making design decisions.

ATDM Strategy Evaluation Dynamic management, control, and influence of: Travel demand, Traffic demand, and Traffic flow Urban street ADTM strategies categorized as belonging to one of four tactical groups Arterial monitoring Signal and speed control Geometric configuration Demand modification tactics Now let’s shift over to the ADTM information provided in Chapter 17. ATDM is the [read first main bullet and sub bullets] There are a wide variety of urban street ADTM strategies. They are typically categorized into one of the four tactical groups listed here [read]. The group name generally describes how a strategy achieves an active traffic demand or management goal. For example, an adaptive signal control strategy is in the “signal and speed control” group because adaptive control uses real-time measurements of speed and volume to control the signal timing.

Example Urban Street ATDM Strategies Adaptive signal control Speed harmonization Transit priority Dynamic lane assignment Reversible lanes Dynamic turn restrictions Dynamic parking Congestion pricing There are many types of ADTM strategies that are applicable to urban street facilities. Some examples are [read]

ATDM Strategy Evaluation Limited knowledge of effects of ATDM strategies Little research to date on the effect of a strategy on demand, capacity, speed, or delay General guidance for evaluation provided Focused on the use of the urban street segment methodology to evaluate... Adaptive control EMS or transit priority Speed harmonization Dynamic lane assignment Reversible lanes The guidance provided in the HCM for evaluating ATDM strategies is characterized as “general.” By this, I mean that specific methodologic steps, procedures, and equations are not provided for evaluating an urban street facility with one or more ATDM strategies. Rather, the guidance provided focuses on the use of the Urban Street Segments methodology in Chapter 18 with some assumptions made about how a strategy may affect operations. The general nature of this guidance stems from the limited knowledge of the effects of ATDM strategies on demand, capacity, speed, or delay. In summary, the guidance describes some extensions to the Chapter-18 methodology to allow it to be adapted to the evaluation of the ATDM strategies listed here [read last five sub bullets].

Session 4 New Capabilities Motorized Vehicle Methodology
Chapter 16: Urban Street Facilities Sustained segment spillback Level of service Chapter 17: Urban Street Reliability and ATDM Travel time reliability Example application of reliability evaluation ATDM strategy evaluation Pedestrian and Bicycle Methodologies OK, we are still working our way through Session 4. We have completed the discussion about the motorized vehicle methodology. We are now going to discuss the new capabilities and changes for the pedestrian and bicycle methodologies. We will take a look at these changes in the next few slides.

Pedestrian Methodology
Facility LOS Score Ip,F Computed as weighted average of segment scores Ip,seg HCM 2010 used segment length L for weight HCM 6th Edition uses travel time for weight 𝐼 𝑝, 𝐹 = 𝐼 𝑝,𝑠𝑒𝑔,𝑖 × 𝐿 𝑖 / 𝐿 𝑖 𝐼 𝑝,𝐹 = 𝑇𝑇 𝑖 𝐼 𝑝,𝑠𝑒𝑔,𝑖 −0.125 / 𝑇𝑇 𝑖 The procedure for calculating the pedestrian segment LOS score has been changed for the HCM 6th Edition. This score is computed as a weighted average of the pedestrian score. The HCM 2010 used segment length “L” as the weighting factor. The HCM 6th Edition uses travel time as the weighting factor. This approach is intended to more appropriately weigh the segment scores when computing the facility score.

Bicycle Methodology Facility LOS Score
Same concept as used for pedestrian method LOS score based on weighted average of segment scores HCM 2010 used segment length for weight HCM 6th Edition uses travel time for weight The bicycle methodology underwent the same change as made for the pedestrian methodology. We just discussed that change. Specifically, the HCM 6th Edition recommends using travel time for the segment weighting factor.

Software Availability
HCS7 – Streets (McTrans) Combines... Signalized intersections Urban street segments Urban street facilities Ramp terminals and alternative intersections Automatic... Supported users can download upgrade There are several software developers that have (or will) implement the new methodology in their software products. One of them, McTrans, is developing a software tool called “Streets”. It will ...[read]

Questions on New Capabilities?
Motorized Vehicle Methodology Chapter 16: Urban Street Facilities Sustained segment spillback Level of service Chapter 17: Urban Street Reliability and ATDM Travel time reliability Example application of reliability evaluation ATDM strategy evaluation Pedestrian and Bicycle Methodologies Questions on New Capabilities? This concludes the session on New Capabilities. Let’s take a few minutes to answer some questions.

Forthcoming Briefings
Closure Forthcoming Briefings Just a reminder of the remaining briefings. There are ___ left. The topics are: [read]

HCM 6th Edition: Urban Street Facilities

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HCM 6th Edition: Urban Street Facilities

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