Highway Capacity Manual fourth edition cover (HCM 2000).
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- Highway Capacity Manual Pdf
The Highway Capacity Manual (HCM) is a publication of the Transportation Research Board of the National Academies of Science in the United States. It contains concepts, guidelines, and computational procedures for computing the capacity and quality of service of various highway facilities, including freeways, highways, arterial roads, roundabouts, signalized and unsignalized intersections, rural highways, and the effects of mass transit, pedestrians, and bicycles on the performance of these systems.[1][2]
There have been six editions with improved and updated procedures from 1950 to 2016, and major updates to the HCM 1985 edition, in 1994, 1997 and 2015.[1][3][2] The HCM has been a worldwide reference for transportation and traffic engineering scholars and practitioners, and also the base of several country specific capacity manuals. The current version, the Highway Capacity Manual, Sixth Edition: A Guide for Multimodal Mobility Analysis, or HCM 2016, or HCM6, was released in October 2016 The sixth edition incorporates the latest research on highway capacity, quality of service, active traffic and demand management, and travel time reliability.[2]
History[edit]
There are more than six decades of research behind the HCM. The first edition of the Highway Capacity Manual was released in 1950 and contained 147 pages broken apart into eight parts. It was the result of a collaborative effort between the Transportation Research Board (TRB) and the Bureau of Public Roads, predecessor to the Federal Highway Administration.[1]
The following editions were published by the Transportation Research Board in 1965, 1985, 2000, 2010 and 2016. The fifth edition HCM 2010 was the culmination of a multiagency effort—including TRB, American Association of State Highway and Transportation Officials (AASHTO), and Federal Highway Administration—over many years to meet the changing analytical needs and to provide contemporary evaluation tools.
In 2013 the Transportation Research Board contracted the development of a major update to the 2010 Highway Capacity Manual. The new and revised material was scheduled to be published as a 2015 interim update of the HCM 2010, known as the HCM 2015 Update.[4][5] The final version, published as the Highway Capacity Manual, Sixth Edition: A Guide for Multimodal Mobility Analysis, or HCM 2016, or HCM6, was released in October 2016 and is available from TRB.[2] The sixth edition incorporates the latest research on highway capacity, quality of service, active traffic and demand management, and travel time reliability.[2]
See also[edit]
References[edit]
- ^ abc'Highway Capacity Manual'. Transportation Research Board, Washington, D.C. 2000. ISBN0-309-06681-6. Chapter 1
- ^ abcdeTransportation Research Board (TRB) (2016-10-24). 'Highway Capacity Manual, Sixth Edition: A Guide for Multimodal Mobility Analysis'. TRB. Retrieved 2016-10-25.
- ^HCM 2010 Major Update
- ^Transportation Research Board (TRB). 'NCHRP 03-115 — Production of a Major Update to the 2010 Highway Capacity Manual'. TRB. Retrieved 2014-04-15.
- ^Transportation Research Board (TRB). 'Workshop on HCM 2015 Update Development'. TRB. Retrieved 2014-04-15.
External links[edit]
- Online Edition of the 2010 Highway Capacity Manual, Transportation Research Board
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Highway_Capacity_Manual&oldid=862527002'
The Highway Design Manual (HDM) establishes uniform policies and procedures to carry out the state highway design functions of the California Department of Transportation. Refer to the 'Foreward' section of the HDM for more information.
Highway Design Manual Change Transmittals are posted by change date and include a summary of the significant changes. Implementation of the current version of the HDM shall be applied to on-going projects in accordance with HDM Index 82.5, unless otherwise noted on the Manual Change Transmittal memo or by separate Design Memo.
No matter which of the formats is used to download and/or print, if the HDM Holder chooses to do so, the Holder is responsible for keeping their electronic and/or paper copy up to date and current. For this reason, HDM Holders are encouraged to use the on-line version of the HDM for the most current design guidance.
Design Information Bulletins (DIB's) and Design Memorandums may supersede this manual.
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Table of Contents
Highway Design Manual (Chapters/Sections) | Last Updated |
---|---|
Inside Cover (PDF) | 7/2/2018 |
Foreword (PDF) | 11/20/2017 |
Table of Contents (PDF) | 12/14/2018 |
Chapter 10: Division of Design (PDF) | 12/14/2018 |
Chapter 20: Designation of Highway Routes (PDF) | 5/7/2012 |
Chapter 40: Federal-Aid (PDF) | 12/30/2015 |
Chapter 60: Nomenclature (PDF) | 7/2/2018 |
Chapter 80: Application of Standards (PDF) | 12/14/2018 |
Chapter 100: Basic Design Policies (PDF) | 12/14/2018 |
Chapter 200: Geometric Design and Structure Standards (PDF) | 12/14/2018 |
Chapter 300: Geometric Cross Section (PDF) | 12/14/2018 |
Chapter 400: Intersections at Grade (PDF) | 12/14/2018 |
Chapter 500: Traffic Interchanges (PDF) | 12/14/2018 |
Chapter 600: Pavement Engineering (PDF) | 11/20/2017 |
Chapter 610: Pavement Engineering Considerations (PDF) | 11/20/2017 |
Chapter 620: Rigid Pavement (PDF) | 11/20/2017 |
Chapter 630: Flexible Pavement (PDF) | 11/20/2017 |
Chapter 640: Composite Pavements (PDF) | 12/30/2015 |
Chapter 650: Pavement Drainage (PDF) | 12/30/2015 |
Chapter 660: Base and Subbase (PDF) | 11/20/2017 |
Chapter 670: Tapers and Shoulder Backing (PDF) | 7/2/2018 |
Chapter 700: Miscellaneous Standards (PDF) | 12/14/2018 |
Chapter 800: General Aspects (PDF) | 12/30/2015 |
Chapter 810: Hydrology (PDF) | 12/30/2015 |
Chapter 820: Cross Drainage (PDF) | 7/1/2015 |
Chapter 830: Transportation Facility Drainage (PDF) | 7/1/2015 |
Chapter 840: Subsurface Drainage (PDF) | 10/4/2010 |
Chapter 850: Physical Standards (PDF) | 12/14/2018 |
Chapter 860: Open Channels (PDF) | 3/7/2014 |
Chapter 870: Bank Protection - Erosion Control (PDF) | 7/15/2016 |
Chapter 880: Shore Protection (PDF) | 7/15/2016 |
Chapter 890: Storm Water Management (PDF) | 9/1/2006 |
Chapter 900: Landscape Architecture (PDF) | 12/14/2018 |
Chapter 1000: Bicycle Transportation Design (PDF) | 7/2/2018 |
Chapter 1100: Highway Traffic Noise Abatement (PDF) | 7/2/2018 |
Index (PDF) | 7/2/2018 |
3.0 Field Measurement of MOEs
This chapter identifies how field measurements are processed to estimate the eight MOEs selected for further investigation in the previous chapter.
3.1 Measuring HCM LOS in the Field
The Highway Capacity Manual to date has used single field measurable performance measures for level of service. For freeways it is density in terms of equivalent passenger cars. For two-lane rural highways it is percent time delay. Divinity original sin 2 source points. For arterial streets it is mean speed of through traffic. For an intersection it is mean delay. The measurement of these performance measures in the field is described below in the following sections.
3.2 Measuring V/C
Volume/capacity (v/c) ratio cannot be measured in the field unless there is a time period when the facility is observably at capacity. [There is a queue of vehicles waiting to be served by the facility that persists for at least 15 continuous minutes.] Then the v/c for any other period can be estimated by taking the ratio of the counted demand to the observed capacity.
3.3 Measuring Travel Time and Speed
The FHWA publication number FHWA-PL-98-035, Travel Time Data Collection Handbook, dated March 1998, prepared by the Texas Transportation Institute provides a complete overview of techniques for gathering travel-time data (see https://www.fhwa.dot.gov/ohim/start.pdf).
There are numerous speed and travel-time measuring techniques, but they can all be grouped into three large categories according to their method of sampling the travel-time universe.
- Spot speed measurement techniques measure vehicle speeds only for a given point of geography or a given point of time.
- Vehicle tracing techniques measure vehicle travel times only for a select portion of all trips.
- Trip maker tracking techniques are similar to vehicle tracing techniques but measure traveler trip times rather than vehicle trip times.
The mechanics of employing many of these techniques are described in the Institute of Transportation Engineers publication, Manual of Transportation Engineering Studies, Edited by H. Douglas Robertson, 2000. The Transportation Research Board Publication, Highway Capacity Manual, 2000 also provides some limited guidance on travel time, speed, and delay data collection in the appendices to Chapters 15 and 16 of the manual.
Spot Speed Measurement Techniques
Spot speed measurement techniques use roadside sensors to measure the instantaneous speeds of vehicles either at specific spots of the roadway or at specific times of the day. These techniques are very cost-effective at gathering large amounts of speed data for specific segments of the transportation system but cannot provide door-to-door travel times.
Roadside sensors include in-the-road loop detectors, roadside radar, microwave sensors, video sensors, and infrared sensors. They are 'location-based sampling' methods which suffer from the biases inherent in measuring speeds at a point and assuming the speed is applicable to other points on the roadway. Technological variations include: single loop detectors, double loop detectors, portable machine double hose counters, radar, lidar, microwave, and infrared sensors, and video camera sensors. Recent technological advances; such as vehicle signature and platoon signature matching, may allow measurements of elapsed time between stations.
Single loop detector occupancies are converted to speeds based upon an estimated average vehicle length during the survey period. This average length varies according to the mix of autos and heavy vehicles present on the facility by time of day and direction.
Radar guns register only the fastest vehicle speed in the platoon, so there may be some upward bias. Also, the 'angle of incidence' (the angle between the road centerline and the hypothetical straight line between the radar gun and the vehicle) of roadside radar and lidar measurements affect the precision of the speed results, but usually the effect is considered negligible.
The minimum sample size is determined based upon the desired confidence interval for the mean speed. Larger variances in measured speeds require larger sample sizes to achieve a desired confidence interval for the mean speed.
Vehicle Tracing Techniques
Vehicle tracing techniques involve tracking either test vehicles or randomly selected vehicles through to determine the travel times between preselected checkpoints. Vehicle tracing techniques are an example of 'trip-based' method of sampling travel times. They are good techniques for measuring trip segment travel times (a geographic portion of the traveler's total trip). However, they generally are not easily adaptable to measurement of door-to-door travel times, because of the expense and difficulty of obtaining a reasonable sample of door-to-door locations.
Vehicle tracing techniques consist of: Test Vehicle, Non-Instrumented Vehicle Tracking, and Passive Probes.
- Test Vehicle (Floating Car) Technique – The test vehicle technique is the most common travel-time collection technique employed to date. This technique consists of hiring a driver and vehicle to drive a vehicle along a preselected route and measuring the elapsed time and distance traversed. The driver is instructed to 'pass as many vehicles as pass him or her' so that the vehicle is in effect driving at the median speed of traffic. Labor saving variations equip the test vehicles with distance measuring instrument (DMI) or global positioning satellite (GPS) to automate measurement and recording and to eliminate the need for a second person in the vehicle.
- Non-Instrumented Vehicle Tracking Technique – This technique uses any one of several technologies for identifying randomly selected vehicles at various checkpoints within the study area and measuring the time between appearances at each checkpoint. Vehicle tracking is different than using test vehicles, because the drivers have not been hired to do the study. The drivers may take different paths and they may make stops in between checkpoints, throwing off the travel-time computations. Technological variations include: License Plate matching, License Plate matching with matching software, and Loop detectors with vehicle signature matching.
- Passive Probe Technique – This technique requires some sort of special tracking instrumentation on the vehicles as well as the roadside. The vehicle driver is not hired to drive a particular route and goes about his or her normal business. Either readers are mounted on the road to record the time and identity of all transponder-equipped vehicles passing by, or readers are mounted in the vehicle to record the times and movements of the vehicle past each transponder location. The drivers may take different paths and they may make stops in between checkpoints, throwing off the travel-time computations. Technological variations include: Automatic vehicle location (AVL), Automatic vehicle identification (AVI), Emergency vehicle tracking, Cellular phone geolocation, and Global positioning satellite (GPS).
- Transit Vehicle Tracking Techniques – The previous vehicle tracing techniques are applicable to all vehicles, including transit vehicles. The discussion under this category focuses on the special issues involved in working with public transit agencies to monitor public transit vehicles. Most public transit operators already publish route schedules and monitor on-time performance. A few operators are able to use automated techniques for tracking vehicle movements, but most currently rely upon manual checkpoint and ride check techniques. The data is stored in varying formats in varying software formats, making electronic transmittal of data difficult.
- Truck Tracking Techniques – Trucks also can be tracked using all of the previously described vehicle tracking techniques. Tracking trucks though requires the active cooperation of the vehicle fleet owner who must consent to the placement of any special devices in the vehicle, or must transcribe manual logs and share the information with interested public agencies. Public agencies wishing to track commercial vehicles must demonstrate to the vehicle fleet owner that the owner will receive some direct benefit in return for the expense of transcribing and sharing the vehicle tracking information. In most cases, travel-time information is mixed in with sensitive proprietary information on customers, and must be manually sorted out by the operator before it can be transmitted to a public agency.
Tripmaker Tracing Techniques
Trip maker tracing techniques survey travelers either after they have completed their trip or recruit volunteers in advance to record and report their travel times as part of their daily activities.
- Retrospective Surveys – Retrospective surveys quiz the traveler about their trip travel times and experiences after the fact. The traveler is not prepped in advance, so questions must be limited to what can be reasonably remembered from the previous day's or that morning's commute. Variations explored here include: household telephone surveys, surveys of employees at their work sites, and web site/e-mail surveys.
- Prospective Surveys – Prospective surveys involve at least two contacts with each individual: one contact to recruit the individual, and a second to collect the information. A third contact may be required to deliver a trip diary form or a GPS unit to the individual to aid in recording information. Travelers can be asked in advance to note a great deal of detail about their trips, including travel times for specific segments of the trip. Technological variations include: global positioning satellite receivers/recorders, e-mail reporting, and cell phone call-in.
HCM Method for Measuring Arterial Speed
Appendix B of Chapter 15 of the Highway Capacity Manual describes the following method for measuring the mean speed of through traffic on an arterial street.
'a. Use the appropriate equipment to obtain [cumulative travel time and stopped delay time]. The equipment may be computerized or simply a pair of stopwatches.
b. Travel times between the centers of signalized intersections should be recorded, along with the location, cause, and duration of each stop.
c. Test-car runs should begin at different time points in the signal cycle to avoid all trips starting first in the platoon.
d. Some mid-block speedometer readings also should be recorded to check on unimpeded travel speeds and how they relate to FFS.
e. Data should be summarized for each segment and each time period, the average travel time, the average stopped time for the signal, and other stops and events (four-way stops, parking disruptions, etc.).
f. The number of test-car runs will depend on the variance in the data. Six to 12 runs may be adequate for each traffic-volume condition.'
3.4 Measuring Delay
The Highway Capacity Manual defines delay as 'The additional travel time experienced by a driver, passenger, or pedestrian.' Delay is thus the difference between an 'ideal' travel time and the actual travel time. Since the definition of delay depends on a hypothetical 'ideal travel time,' delay is not always directly measurable in the field.
If the ideal travel time is defined as the off-peak travel time, then the measured delay is the difference between the actual measured travel time during the peak period, and the actual measured travel time during the off-peak period.
If the ideal travel time is defined as travel at the posted speed limit, then the delay cannot be directly measured in the field. It is estimated by subtracting the hypothetical travel time at the posted speed limit from the measured mean travel time in the field.
HCM Method for Measuring Free-Flow Speed
Appendix B of Chapter 15 of the Year 2000 Highway Capacity Manual explains how to measure the free-flow speed for an arterial street.
'This can be determined by making runs with a test car equipped with a calibrated speedometer during periods of low volume. An observer should read the speedometer at mid-block locations when the vehicle is not impeded by other vehicles and record speed readings for each segment. These observations can be supplemented by spot speed studies at typical mid-block locations during low-volume conditions.'
HCM Method for Measuring Intersection Control Delay
The Year 2000 Highway Capacity Manual (see Appendix A, page 16-90 of the HCM) describes the following field procedure for measuring and computing intersection control delay for a signalized intersection.
- The survey should begin at the start of the red phase of the lane group.
- At regular intervals of between 10 and 20 seconds (but not an interval length that is evenly divisible into the cycle length) count the number of queued vehicles.
- A vehicle is considered as queued when it approaches within one car length of a stopped vehicle and is itself about to stop.
- All vehicles that join a queue are then included in the vehicle-in-queue counts until the rear axle of the vehicle crosses the stop line.
- Simultaneously count the total number of arriving vehicles (whether they stop or not).
- At the end of the survey period, continue counting vehicles in queue for all vehicles that arrived during the survey period until all of them have exited the intersection. This step requires mentally noting the last stopping vehicle that arrived during the survey period in each lane of the lane group and continuing the vehicle-in-queue counts until the last stopping vehicle or vehicles, plus all vehicles in front of the last stopping vehicles, exit the intersection. Stopping vehicles that arrive after the end of the survey period are not included in the final vehicle-in-queue counts.
The time in-queue per vehicle is equal to 90 percent of the interval between queue counts multiplied by the sum of the vehicles in queue each interval divided by the total arriving vehicles. The 90 percent factor is intended to correct for the tendency of this method to over count delay.
[Equation 1]
[Equation 2]
Where:
- D = Average control delay per vehicle (secs).
- TQ = Time in-queue per vehicle (secs).
- I = The interval (length of time) between queue counts (secs).
- Q(i) = The number of vehicles in queue at time point 'i.'
- V = Total arriving volume of vehicles (whether or not queuing).
- CF = Correction Factor to convert stopped delay to control delay.
- VS = Number of arriving vehicles stopping.
The correction factor is determined from the following look-up table taken from Exhibit A16-2 of the HCM (see Table 12).
Table 12. Acceleration-Deceleration Delay Correction Factor, CF(s)
Free-Flow Speed | <= 7 Vehicles | 8-19 Vehicles | 20-30 Vehicles |
---|---|---|---|
<=37 mph | +5 | +2 | -1 |
>37-45 mph | +7 | +4 | +2 |
> 45 mph | +9 | +7 | +5 |
Source: Exhibit A16-2, Highway Capacity Manual, Transportation Research Board, 2000.
3.5 Measuring Queues
According to the ITE Manual of Transportation Engineering Studies, the macroscopic approach to measuring queues is to count the arrival and departure volumes for facility aggregated to five-minute intervals. The count should start before any queues are present and it should not end until the queues have all cleared. The difference between the cumulative five-minute arrivals and the five-minute departures is the number of vehicles in queue. The arrival data must be counted just upstream of the end of the longest expected queue.
For a microscopic analysis, the license plate, arrival time, and departure time of each vehicle is recorded. The number of vehicles in queue at any point in time is the difference between the cumulative number of arrivals up to that point minus the cumulative departures up to that point in time.
The Year 2000 Highway Capacity Manual (HCM) defines a Queue as: 'A line of vehicles, bicycles, or persons waiting to be served by the system in which the flow rate from the front of the queue determines the average speed within the queue. Slowly moving vehicles or people joining the rear of the queue are usually considered part of the queue. The internal queue dynamics can involve starts and stops. A faster-moving line of vehicles is often referred to as a moving queue or a platoon.'
The HCM defines the Back of Queue as: 'The distance between the stop line of a signalized intersection and the farthest reach of an upstream queue, expressed as a number of vehicles. The vehicles previously stopped at the front of the queue are counted even if they begin moving.'
The HCM method described above for measuring control delay at a signal also can be used to measure queues.
3.6 Measuring Stops
The number of stops is can be obtained from a floating car survey, where the number of stops during each run is recorded. The number of stops obtained in this manner is representative only of vehicles driving the same path as the floating cars (usually just through traffic on the arterial). Ship sinking simulator 2 download.
Similarly, the HCM control delay measurement method described above can be used to identify the number of vehicles stopping on the approach to a traffic signal.
3.7 Measuring Density
The Year 2000 Highway Capacity Manual does not describe a method for directly measuring density in the field.
Aerial photography has been used to measure densities on freeways in several cities for the purposes of congestion monitoring (see Santa Clara VTA Annual Congestion Monitoring Reports for an example). A single photo is shot every half hour during the peak period and the number of vehicles counted between interchanges to obtain an average density representative of that half-hour period for each segment of the freeway facility. Vehicle density is NOT converted to passenger car equivalents.
Highway Capacity Manual 6th Edition Pdf Download
Alternatively, density can be computed from loop detector measurements of speed and flow using the fundamental relation d=v/s (shown in HCM, equation 23-4, page 23-12), where 'v' is the flow rate in vehicles per hour, 'd' is the density in vehicles per mile, and 's' is the speed in mph.
The volume is counted manually, with temporary machine counters, or with permanent loop detectors for the desired analysis period. If an axle counter is used then an adjustment may be made to the count based on a separate truck axle count (See ITE Manual of Transportation Engineering Studies).
The spot speed is measured using any one of a variety of devices (see Measuring Speed, above). A sample size is selected to reduce the confidence interval for the true mean speed to the desired size.
Highway Capacity Manual Online
3.8 Measuring Variance of Travel Time
The variance of travel time is not usually measured because of the expense involved. An agency may take the inverse of speed (travel time per mile) measured at loop detectors and compute the variance of the travel time per mile at the detectors.
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This is Volume 4 for the HCM 2010. To access Volume 4 for the HCM 6th Edition, first published in 2016, please visit hcmvolume4.org.
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The HCM was divided into multiple volumes as part of the 2010 Manual production. Volumes 1-3 are part of the printed Manual. Volume 4 is an online resource that provides a wealth of information never before provided to HCM users. Resources include:
- Supplemental chapters that provide extensive methodological details for several HCM chapters in Volume 1-3.
- Interpretations and errata to HCM methods and chapters.
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- A discussion forum that allows users to come together to ask questions and collaborate on HCM related matters.
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Recent and Pending Changesto Chapter 9 of the
Highway Capacity Manual
(Signalized Intersections)
Dennis W. Strong, P.E.
President, Strong Concepts
Chairman, HCM Signals Subcommittee
Abstract:
The Highway Capacity Manual (HCM) is published by the Transportation Research Board as a means of standardizing the techniques used to evaluate the quality of service provided by various transportation facilities. Chapter 9 of the HCM provides detailed methodologies and procedures for the analysis of capacity, delay and level of service for signalized intersections. This chapter is possibly the most complicated and probably the most used chapter of the Manual, and considerable research funding has been directed at signalized intersections. These considerations have led to the recent 1997 publication of a major update to Chapter 9, with another update pending for 2000. The subject of this paper is a summary of the major changes which have occurred in these new versions of Chapter 9, and a reflection on how these changes will manifest themselves in our daily work. A technical paper focused on the details of the changes was presented by the author at the 79th Annual Meeting of the Transportation Research Board this past January.
1997 Changes to the Highway Capacity Manual
A number of significant changes have been made to Chapter 9 of the HCM in the 1997 update. These changes are a result of the efforts of the HCM Signals Subcommittee to review research reports and other suggested changes made since the 1994 HCM was published, and to assemble these changes into a cohesive update of Chapter 9 which would advance the state of the art for capacity analysis of signalized intersections. These changes may be categorized into five major areas:
- New Use of Control Delay
- New Model for Oversaturated Delay
- Improved Definition and Use for Lost Time
- New Treatment of Actuated/Coordinated Movements
- Miscellaneous Changes
Each of these major areas of change and their impact are described in the following paragraphs.
New Use of Control Delay
Prior versions of the Highway Capacity Manual (1985 and 1994) used 'stopped delay' as the measure of effectiveness (MOE) for the performance of signalized intersections. This was due to a perception that stopped delay, the amount of time a vehicle was physically stopped on the pavement, was an easier performance measure for a driver to perceive and for traffic personnel to survey. The difficulty which resulted was that virtually all other related methodologies and software used 'total delay', which made comparison of the HCM results to other models difficult. Even other chapters of the HCM such as Unsignalized Intersections (Chapter 10) and Arterial Streets (Chapter 11) used total delay as the primary MOE. In order to be more consistent with all of these other methodologies, it was decided that the 1997 HCM should also use total delay as its MOE for signalized intersections, so the necessary adjustments were made. Effectively, the divisor of 1.3 which had previously been used to convert a total delay model to represent stopped delay was simply removed from the delay formulas and the delay thresholds for level of service were increased by this same 1.3 factor. New survey techniques were also developed to survey the new total delay quantity, and it turns out these techniques are no more difficult than those used previously. The new delay value is also being called 'control delay' to reflect that it is the delay which results from the traffic control device only, and that other delay values such as geometric delay or incident delay will contribute to the real 'total delay'.
This change will result in the reporting of 30 percent higher delay values, with the appearance that the level of service delay thresholds are more lenient than before by allowing these higher delays to result in lower levels of service than before. The reason is, of course, because we're reporting a different delay value than before and the thresholds have compensated for this. For example, with all other concerns remaining equal, a previous calculation of 25.0 seconds of stopped delay will now result in a calculation of 32.5 seconds of control delay (25.0 x 1.3 = 32.5). This is the reason the level of service C threshold has been raised from 25 to 35 seconds (rounded 'up' from 32.5). In the short term we'll struggle to get used to these new, higher values and what appears to be a higher tolerance for delay. In reality, this change is more of a cosmetic change that by itself doesn't really have a significant impact of level of service results.
New Model for Oversaturated Delay
A major limitation of the HCM signalized method has been its inability to quantify the delay which resulted from an oversaturated situation. This limitation caused significant problems when evaluating problem intersections, especially when attempting to compare before and after calculations. The problem was in the original formulation of the delay equation used in the 1985 HCM where the manual stated that conditions with volumes that exceeded capacities by more than 20 percent could not be calculated using the delay formula. Since that time the Federal Highway Administration has commissioned a study which determined, in part, that a minor change could be made to the delay equation which would allow oversaturated conditions to be evaluated. With this in mind, the HCM Committee decided that this change should be implemented, along with several related changes. These changes now allow delays to be calculated without any limits on the volume-to-capacity ratio, as well as for conditions where oversaturation exists for more than 15 minutes.
Highway Capacity Manual Pdf
The impact of this change is that users of the HCM will now be able to better and more completely evaluate problem conditions which involve oversaturation, as well as to quantify how much these conditions can be improved. These new procedures, which also now allow analysis for conditions which have a queue at the beginning of the study period, will permit more complete and comprehensive multi-period analyses which span across an entire peak period of time-varying demands, resulting in more accurate and useful peak period analyses for evaluating congestion management alternatives.
Improved Definition and Use for Lost Time
The 1985 and 1994 HCM's were quite casual in their definition and recommendations for use of the lost time quantity needed for calculating signalized intersection delay. The value was properly defined, but since little advice was provided for determining values to be used, the published default value of 3 seconds was frequently used by users of the HCM, even when changes were made to intersection analyses which would affect the lost time. To correct this problem, the inputs required of the user have been changed so that the lost time needed is calculated from these inputs rather than being input directly. These new inputs, startup lost time and extension of effective green, are formulated so that the ending lost time can be calculated from the input value of yellow and all-red time, and is therefore determined by the length of the clearance period. Thus, when a clearance period is changed, the total lost time will change by an equal amount unless the user specifically prevents this from happening. Consequently, when default values of the inputs are used, the lost time will be dependent on the clearance value, a feature which did not exist in previous versions.
The impact of this subtle change to the procedures can be quite significant, and may be quite apparent in capacity analyses performed with both the old and new methods, especially where default values are used. For example, when default values are used in the new method, the total lost time which results for each signal phase will be equal to the total yellow and all-red clearance time for each phase. Since clearance times are frequently found to be 5 to 6 seconds, lost time values in this range for the new analysis will be significantly higher than the default value of 3 seconds found in the old analysis. This can result in a reduction of useable greentime throughout a cycle of as much as 10 or more seconds for multi-phase signals (in comparison to the old analysis) which can be quite significant for medium to short cycles. The net effect can easily be a drop of one or even two levels of service between the two analyses if all other things are equal. This can be quite an eye-opener, all due to a subtle and apparently minor change to the way lost time is determined.
New Treatment of Actuated/Coordinated Movements
The HCM has long-needed an improved way of assessing the impact that actuated movements have on a signal's operation. Previously, the model simply stated that the impact of an actuated movement was a reduction of the primary delay by 15 percent, regardless of the quality or specifics of the actuation provided. Recently a National Cooperative Highway Research Project study was completed which aimed at improving this HCM model. Essentially the recommended changes from this study came in two parts: a change to the delay equation which made it sensitive to the extension value of the actuated movement, and a better way to estimate the average greentimes for an actuated signal which would be used in the capacity analysis. These changes were implemented directly in the 1997 update. This also simplifies the adjustments which are made for coordinated signals, and a related adjustment was added to account for the affect of congested upstream conditions. The result is that our capacity analyses can now reflect to a greater degree how the values of various actuated control parameters such as initial, extension, maximum, detector size, detector setback, etc. affect signalized delay.
Miscellaneous Changes
Several miscellaneous changes were also made which warrant brief mention due to their significance. One is that lane utilization factors are now used to reduce saturation flow instead of fictitiously increasing demand. With this change volume-to-capacity ratios will remain nominally unchanged with a more realistic way to account for unbalanced lane use and no need to create fictitious vehicles. The new method will also result in saturation flow rates which are more appropriate for use in other traffic models such as TRANSYT, PASSER and CORSIM, and will create greater consistency between analyses done with the HCM procedures and these other models
Another change affects several of the factors involved in the permitted left turn model. In this regard, the left-turn equivalency model has been improved, simplified and adjusted to reflect the changes in lane utilization procedures, and several of the other sub-models have been improved with better formulas and more logical limits. The net effect is that the permitted left turn model should deliver more reliable results over a wider range of conditions, thus improving our overall accuracy when using the HCM capacity method under these conditions.
Other minor change included the further clarification of an often-misunderstood reality that an HCM capacity analysis is normally performed for a 15-minute peak. Thus, the use of peak hour factors is merely to estimate these peak 15-minute flow rates when the 15-minute flow rates are not otherwise available. Consequently, since 15-minute counts are typically performed, the flow rates for the intersection's peak 15-minute period should be determined and peak hour factors should not be used (set equal to 1). The use of the CBD adjustment factor was also clarified, and minor errata from the 1994 publication were incorporated.
2000 Changes to the Highway Capacity Manual
A number of important additional changes have been made to Chapter 9 of the 1997 HCM which will appear in a pending 2000 update. These changes include:
- Re-organized Chapters and Editorial Changes
- New Model for Queue Lengths
- New Adjustments for Pedestrians and Bicycles
- Protected-Permitted Left Turn Model Changes
Each of these major areas of change and their impacts are described in detail below.
Re-organized Chapters and Editorial Changes
The Highway Capacity Manual 2000 (HCM2000) represents a major overhaul of the three prior versions of the manual released in 1985, 1994 and 1997. The entire HCM has been completely re-organized with over 30 chapters, and will come in both a printed manual and as a multi-media CD-ROM. Many completely new chapters and procedures have been developed for the HCM2000, but the signalized intersection materials are fundamentally the same as in the 1997 version, with the exception of the items discussed below. Even so, the signalized materials have been substantially enhanced with new figures and discussions, and the new layout of the HCM makes the materials much easier to read and understand. Many of the complex procedures of the signalized method have also been relocated to appendices, making the basic procedures easier to follow.
In the new organization of the HCM 2000 the signalized intersection materials have been divided into two chapters. Chapter 10 contains general concepts for all interrupted flow facilities, including signals, stop signs, roundabouts and arterials. This chapter provides discussions of general concepts which are common to more than one interrupted flow facility type, as well as general concepts specific to each individual facility. Chapter 10 also contains the materials which relate to planning uses of the signalized method. Chapter 16 is the chapter which now contains the primary methodology for signalized intersection analysis.
New Model for Queue Lengths
The Highway Capacity Manual has never had a formal queue model which users could use to estimate queue backups for both signalized intersection evaluation and design. This has been a long-standing need of the HCM, and with its continued omission from the manual users have used a wide variety of queue models which deliver widely varying results due to their inconsistent formulations. To address this critical need, the HCM2000 development project conducted a literature review to determine the specific needs users had for a comprehensive queue model, then set out to develop such a model that met these needs. The publication of the HCM2000 will see the fruits of that effort in a comprehensive queue model which includes the effects of specific signalized conditions including greentime, cycle length, phasing, saturation flow rate, capacity, coordination, actuation, oversaturation and initial queue. This model estimates the most important part of the queue, the extent of the back of the queue measured from the stop bar, and will also estimate various degrees of confidence in the form of percentile values.
The existence of a formal queue model in the HCM will provide for the first time a national standard for estimating queue lengths, and as a result will generate some consistency across the country on how this estimation is done. Hopefully, this will also lead to a similar consistency in the queue models used in various software packages, which presently run the gamut of possible queue models. In addition, for the first time we will have a comprehensive queue model that is sensitive to all the signalized conditions we need to consider when modeling queues so we can begin making more informed decisions and designs in this regard.
New Adjustments for Pedestrians and Bicycles
A Federal Highway Administration research project was recently completed which detailed the effect that pedestrians and bicycles have on turning traffic at signalized intersections. The results of this research have been implemented in the HCM2000 in a manner that now allows us to quantify in a much more detailed and precise way how these alternate modes will affect signal operation and performance. These effects, which were previously included in the turning traffic adjustment factors, have now been separated out into their own satflow adjustment factors so they can be modeled separately and the effects of various designs can be observed directly. This is an important step forward for facilities where pedestrians and/or bicycles are a significant part of the total traffic mix.
Protected-Permitted Left Turn Model Changes
Yet another minor improvement has been made to the permitted left turn model in a continuing effort to make this complex model as realistic as possible. In the HCM2000 an older model for treating protected-permitted left turns which make their movement from a shared through lane (called Case 6 turns) has been updated so it is consistent with how both the protected and permitted movements are made on their own from a shared lane, as well as consistent with how a protected-permitted turn is handled from an exclusive turn lane. New terminology for this condition has also been established so it can be concisely described without a mouthful of words: the complete old terminology was 'protected-plus-permitted or permitted-plus-protected left turn' where the new terminology is simply 'compound left turn'.
Summary
The changes made to the signalized intersections methods of the Highway Capacity Manual in 1997 and 2000 constitute major improvements in our ability to model signalized intersection conditions more accurately. As a result, we have been empowered to make better assessments of the impacts of various potential or projected changes to our signalized conditions, as well as to create better designs to accommodate these conditions in the future.
this page last updated March 11, 2004