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Chapter 13: Fundamental Concepts for Uninterrupted Flow Facilities

Chapter 13: Fundamental Concepts for Uninterrupted Flow Facilities. Chapter objectives: By the end of this chapter the student will be able to:. Explain why capacity is the heart of transportation issues.

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Chapter 13: Fundamental Concepts for Uninterrupted Flow Facilities

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  1. Chapter 13: Fundamental Concepts for Uninterrupted Flow Facilities Chapter objectives: By the end of this chapter the student will be able to: • Explain why capacity is the heart of transportation issues. • Define capacity and level-of-service concept and explain why capacity is not a fixed value • Explain the difference between “service flow rates” and “service volumes” • Explain the relationship between the v/c ratio and level of service • Discuss problems related to the use of level of service (LOS) Chapter 13

  2. 13.1 Types of Uninterrupted Flow Facilities • We studied this one. Can you explain? Chapter 13

  3. 13.2 The Highway Capacity Manual • How much traffic a given facility can accommodate? • Under what operating conditions can it accommodate that much traffic? Highway Capacity Manual (HCM) • 1950 HCM by the Bureau of Public Roads • 1965 HCM by the TRB • 1985 HCM by the TRB (Highway Capacity Software published) • 1994 updates to 1985 HCM • 1997 updates to 1994 HCM • 2001 updates to 2000 HCM • 2010 HCM was published in April 2011. Chapter 13

  4. Highway capacity software (HCM 2010) Just show where it can be found on CAEDM. Chapter 13

  5. 13.3 The Capacity Concept HCM analyses are usually for the peak (worst) 15-min period. The capacity of a facility is: “the maximumhourly rate at which persons or vehicles can be reasonably expectedto traverse a point or uniform segment of a lane or roadway during a given time periodunder prevailing roadway, traffic, and control conditions.” Sometimes using persons makes more sense, like transit Some regularity expected (although capacity is not a fixed value) With different prevailing conditions, different capacities result. • Traffic • Roadway • Control Chapter 13

  6. 13.3.3 Current Values of Capacity for Uninterrupted Flow Facilities Chapter 13

  7. 13.4 The Level of Service Concept & 13.5 Service Flow Rates and Service Volumes “Level of service (LOS) is a quality measure of the effect of a number of factors, which include speed and travel time, traffic interruptions, freedom to maneuver, safety, driving comfort and convenience, and operating cost.” LOS A (best) LOS F (worst or system breakdown) Service Flow Rate, SFA SFB SFC SFD SFE Chapter 13

  8. MOE in 2010 HCM Chapter 13

  9. Rate of flow v/c = Capacity 13.6 The v/c Ratio and Its Use in Capacity Analysis The comparison of true demand flows to capacity is a principal objective of capacity and LOS analysis. The volume capacity ratio indicates the proportion of the facility’s capacity being utilized by current or projected traffic.  Used as a measure of the sufficiency of existing or proposed capacity. v/c is usually less than or equal to 1.0. However, if a projected rate of flow is used, it may become greater than 1.0. The actual v/c cannot be greater than 1.0 if departure volume is used for v. A v/c ratio above 1.0 predicts that the planned design facility will operationally fail! Queue will form. Chapter 13

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