Chapter 241 Chapter 25: Analysis of Arterial Performance Know how arterial LOS is defined Be able to determine arterial classes Know how to determine arterial speed Learn arterial speed, intersection delay, and signal spacing are intricately related Understand how sensitive arterial LOS is to signal spacing, progression quality and cycle length. Chapter objectives: By the end of this chapter the student will:

Chapter 242 Definition of an Arterial Segment An arterial segment contains one signalized intersection at its downstream end. An arterial section is a series of adjacent segments that are analyzed as a unit.

Chapter 243 The arterial LOS is based on the average travel speed of the through vehicles on the arterial under considerations.

Chapter 244 Arterial LOS (Class must be defined first) Before determining LOS, the user must classify arterials. See the next page for examples.

Chapter Determining Arterial Class (Signalized intersection spacing, Free flow speed, and location) Class I. Arterials in nonrural areas with FFS of at least 45 mph and a signal density of less than 2 signalized intersections per mile—or arterials in rural developed areas. Class II. Arterials with FFS of 35 mph to 45 mph and a signal density of 2 to 4.5 signals per mile. Class III. Arterials with FFS of 30 to 35 mph and a signal density of at least 4.5 signals per mile. Class IV. Arterials in urban downtown areas of population 750,000 or more—or arterials with FFS of 25 to 35 mph and a signal density of 7 to 12 signals per mile

Chapter 246 Some of them are obvious. Xi’an, Looking south to the South Gate from the Bell Tower (Severe air pollution)

Chapter 247 Determining arterial classes Categorize the arterial using these descriptions.

Chapter Basic Performance Concepts 1. Free-flow speed. The speed most drivers would choose on the arterial if they had green lights and were alone in their direction of movement 2. Running speed (or Ave. running speed). The average speed of vehicles while in motion. It might be 5 to 10 mph lower than the FFS. 3. Average travel speed. The actual speed with the additional effect of signals and all other stops and delays added. LOS uses this speed Arterial Speed Concept

Chapter Determination of arterial speed Arterial speed – a function of control delays at the signalized intersections and running time between signalized intersections. d3d3 Control delay component:

Chapter 2410 Recommended “I” values for d 2 If there is significant amount of mid-block delay, it must be added to the denominator of Equation 25-1.

Chapter 2411 Estimating running time on arterial segments (HCM data)

Chapter 2412 Estimating running time on arterial segments (FDOT data)

Chapter 2413 Do Example 25-1

Chapter Sensitivities The Impact of Signal Spacing on Arterial Performance Arterial Speed Watch out for the direction of y-axis! Less signal spacing = more signals/mile  more delay, slower arterial speed

Chapter & Impact of progression quality and cycle length on arterial speed

Chapter Through Vehicles on the Arterial The HCM defines arterial performance in terms of through vehicles. The primary function of an arterial is to move through vehicles, hence, the definition is correct. But the HCM signalized intersection analysis uses lane group. There is no way to separate delays for through vehicles from for turning vehicles if they use shared lanes. The difference between the average travel speed of the through vehicles and average travel speed of all vehicles on any given link was found to be about 4 to 5 mph.

Chapter Arterial vs. Intersection LOS (This is the most important section of this chapter.) Average arterial speed in terms of intersections per mile, assuming a constant link length and intersections with similar delays. Note that this equation assumes RT mi and d i are the same for all signalized intersections and their upstream segments.

Chapter 2418 Example (p.737) Class III arterial, 10 signals, 0.1 mile/segment Delay = 6.4 sec at each signalized intersection, LOS A. 35 mph, from Table 25.4 Class III, 0.1 mile/segment, and FFS = 35 mph, travel time = 145 sec per mile ART SPD = 3,600/[145 sec + 10*6.4 sec] = 17.2 mph Table 25.1 says, LOS D. Signal spacing can and does affect the quality of the arterial trip. See 25.6 to understand how difficult it is to maintain higher average travel speed on arterials! (In this case, running speed = 40 mph, with signals arterial speed 30 to 35 mph desired.