lecture week 2 and3

8/17/2019 LECTURE Week 2 And3

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GENERAL FRAMEWORK

Conceptual guide of HCM 2010“The Highway Capacity Manual (HCM) can beapplied to transportation applications thatrange from the highly detailed to the highlygeneralized, to roadway system elements thatrange from individual points to an entiretransportation system, to four travel modesthat can be considered separately or in

combination, and to several types of roadwayand facility operating conditions”…

The HCM can be applied for:

1. Operational,

2. Design,

3. Preliminary engineering planning andanalysis


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3/9/2016 COPYRIGHT @ AKRAM, FKA UiTM 4


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Visualize the future….

Overall Schematic framework


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HOW TO EVALUATE THE

PERFORMANCE….?

OPERATING CONDITION -TWO PARTS1. UNINTERRUPTED FLOW

2. INTERRUPTED FLOW

REGIME FLOW -THREE PARTS1. UNDERSATURATED FLOW2. OVERSATURATED FLOW

3. QUEUE DISCHARGE FLOW


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UNINTERRUPTED FLOW

• Uninterrupted‐flow facilities have no fixed causes of delay or

interruption external to the traffic stream.

•

Volume 2of the HCM provides analysis methodologies forinterrupted‐flow facilities

• Freeways and their components operate under the purest

form of uninterrupted flow. Not only there are no fixed

interruptions to traffic flow, but access is controlled and

limited to ramp locations.

• Multilane highways and two-lane highways can also operate

under uninterrupted flow in long segments between points of

fixed interruption. On multilane and two‐lane highways, it is

often necessary to examine points of fixed interruption (e.g.,

traffic signals) as well as uninterrupted‐flow segments.

• The traffic stream on uninterrupted‐flow facilities is the resultof individual vehicles interacting with each other and the

facility’s geometric characteristics.

Interrupted‐Flow Facilities

• Interrupted‐flow facilities have fixed causes of periodic delay or interruption tothe traffic stream, such as traffic signals and STOP signs.

• Urban streets are the most common form of this kind of facility. Exclusivepedestrian and bicycle facilities are also treated as interrupted flow, since theymay occasionally intersect other streets at locations where pedestrians andbicyclists do not automatically receive the right‐of‐way.

• Volume 3 of the HCM provides analysis methodologies for interrupted‐flow

facilities.

• The traffic flow patterns on an interrupted‐flow facility are the result not only ofvehicle interactions and the facility’s geometric characteristics but also of thetraffic control used at intersections and the frequency of access points to thefacility. Traffic signals, for example, allow designated movements to occur onyduring certain portions of the signal cycle (and, therefore, only during certainportions of an hour).


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UNDERSATURATED FLOW

Traffic flow during the analysis period isspecified as “undersaturated” when thefollowing conditions are satisfied

(a) the arrival flow rate is lower than thecapacity of a point or segment,

(b) no residual queue remains from a priorbreakdown of the facility,

(c) traffic flow is unaffected by downstreamconditions.

• Uninterrupted‐flow facilities operating in a state ofundersaturated flow will typically have travel speedswithin 10% to 20% of the facility’s free‐flow speed,even at high flow rates, assuming base conditions (e.g.,level grades, standard lane widths).

• On interrupted‐flow facilities, queues form as a natural

consequence of the interruptions to traffic flowcreated by traffic signals and STOP and YIELD signs.Therefore, travel speeds are typically 30% to 65%below the facility’s free‐flow speed in undersaturatedconditions


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OVERSATURATED FLOW

Traffic flow during an analysis period ischaracterized as “oversaturated”when any ofthe following conditions is satisfied:

(a) the arrival flow rate exceeds the capacity of apoint or segment,

(b) a queue created from a prior breakdown of

a facility has not yet dissipated,

(c) traffic flow is affected by downstreamconditions.

• On uninterrupted‐flow facilities, oversaturatedconditions result from a bottleneck on the facility.During periods of oversaturation, queues form andextend backward from the bottleneck point. Trafficspeeds and flows drop. Significantly as a result ofturbulence, and they can vary considerably, dependingon the severity of the bottleneck.

• Freeway queues differ from queues at undersaturatedsignalized intersections in that they are not static or“standing.” On freeways, vehicles move slowly through

a queue, with periods of stopping and movement. Evenafter the demand at the back of the queue drops, ittakes some time for the queue to dissipate becausevehicles discharge from the queue at a slower rate thanthey do under free‐flow conditions


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QUEUE DISCHARGE FLOW

• A third type of flow, queue discharge flow, isparticularly relevant for uninterrupted‐flowfacilities.

• Queue discharge flow represents traffic flow thathas just passed through a bottleneck and, in theabsence of another bottleneck downstream, isaccelerating back to the facility’s free‐flow speed.Queue discharge flow is characterized by

relatively stable flow as long as the effects ofanother bottleneck downstream are not present.

Expressway/Freeway ref: chapter 10 hcm 2010

chapter 11 hcm 2010

Note: Conversion units ; HCM 2010 using US metric only

1 Foot = 0.0003048 kilometers1 miles per hour = 1.609 kilometers per hour


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Some of the differencesHCM 2000 Vs HCM 2010


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FREEWAY FACILITIES

• IN GENERAL AS INTRO..

• A freeway facility is composed of three types of segments.

• Weaving segments are segments of the freeway where two or more vehicle flowsmust cross each other’s path. They are usually formed when merge areas arefollowed by diverge areas. They are also formed when an on-ramp is followed byan off-ramp and the two are connected by an auxiliary lane.

• Ramp segments are points at which on- and off-ramps join the freeway. The junction formed at this point is an area of turbulence due to concentrations ofmerging or diverging vehicles.

•Basic freeway segments are outside the influence area of ramps orweaving segments of the freeway.



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BASIC FREEWAY SEGMENTS

“Basic freeway segments are defined as those

freeway segments that are outside the influence

of merging, diverging, or weaving maneuvers. In

general, this means that lane‐changing activity is

not significantly influenced by the presence oframps and weaving segments. Lane‐changing

activity primarily reflects the normal desire of

drivers to optimize their efficiency through lane

changing and passing maneuvers”.


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BASE CONDITIONS

• The base conditions under which the full capacityof a basic freeway segment is achieved includegood weather, good visibility, no incidents oraccidents, no work zone activity, and nopavement deterioration serious enough to affectoperations.

• This methodology assumes that these conditionsexist. If any of these conditions do not exist, thespeed, LOS, and capacity of the freeway segment

can be expected to be worse than thosepredicted by this methodology.

• Base conditions also include the followingconditions, which can be adjusted as themethodology is applied to address situations inwhich these conditions do not exist:

• No heavy vehicles [trucks, buses, recreationalvehicles (RVs)] in the traffic stream;

• A driver population composed primarily ofregular users who are familiar with the facility;and

• Minimum 12‐ft (3.6 meter) lane widths and 6‐ftright‐side clearances.


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Types of Flow

Refer to last week asignmnet….?


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Speed−Flow Curves for Base

Conditions

Refer details not “do” and “don’t”


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The research leading to these curves (1, 2) found that several factors affect

the FFS of a basic freeway segment, including the lane width, right‐shoulder

clearance, and ramp density. Ramp density is the average number of

on‐ramps plus off‐ramps in a 6‐mi range, 3 mi upstream and 3 mi

downstream of the midpoint of the study segment. Many other factors are

likely to influence FFS: horizontal and vertical alignment, posted speed limits,

level of speed enforcement, lighting conditions, and weather. Although thesefactors may affect FFS, little information is available that would allow their

quantification

CAPACITY UNDER BASE CONDITIONS


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LOS FOR BASIC FREEWAY SEGMENTS

LOS on a basic freeway segment is defined bydensity. Although speed is a major concern ofdrivers as related to service quality, it would bedifficult to describe LOS by using speed, since itremains constant up to flow rates of 1,000 to 1,800pc/h/ln, depending on the FFS. Density describesthe proximity to other vehicles and is related to thefreedom to maneuver within the traffic stream.

Unlike speed, however, density is sensitive to flowrates throughout the range of flows.


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LOS criteria• A basic freeway segment can be characterized by three

performance measures: density in passenger cars permile per lane (pc/mi/ln), space mean speed in milesper hour (mi/h), and the ratio of demand flow rate tocapacity (v /c). Each of these measures is an indicationof how well traffic is being accommodated by the basicfreeway segment.

• Because speed is constant through a broad range offlows and the v /c ratio is not directly discernible toroad users (except at capacity), the service measure forbasic freeway segments is density. Exhibit 11‐5 shows

the criteria.


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REQUIRED INPUT DATA


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APPLICATIONS

The methodology in this chapter is relatively straightforward, so it can be directly usedin any one of four applications:

1. Operational analysis: All traffic and roadway conditions are specified for an existingfacility or a future facility with forecast conditions. The existing or expected LOS isdetermined.

2. Design analysis: A forecast demand volume is used, and key design parameters arespecified (e.g., lane width and lateral clearance). The number of lanes required todeliver a target LOS is determined.

3. Planning and preliminary engineering: The basic scenario is the same as that fordesign analysis, except that the analysis is conducted at a much earlier stage of thedevelopment process. Inputs include default values, and the demand volume isusually stated as an annual average daily traffic (AADT) value.

4. Service flow rates and service volumes: The service flow rate, service volume, or

daily service volume, or all three, are estimated for each LOS for an existing or futurefacility. All traffic and roadway conditions must be specified for this type of analysis.


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lecture week 2 and3

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