S8_level-service-los2.pdf

TRANSPORTATION ENGINEERING Explanatory Session: «Level of Service (LOS)»

CONTENTS

Capacity and Level of Service

Freeway and Highway LOS

LOS Exercises

Capacity and LOS

CAPACITY AND LEVELS OF SERVICE  The previous class and earlier today we focused on:  Flow  Concentration  Average Speed  However, measuring these values for each highway or roadway

segment would take too much resources not always available.  Even more, taking such values for a non-existent roadways is physically impossible.  Therefore, it is the job of the Transportation Engineer to anticipate the values of the operational characteristics of the roadways so that they can be properly designed geometrically

CAPACITY AND LEVELS OF SERVICE  Such observations are based on:  Observe the existing conditions of similar roadways or

conditions (e.g. your previous homework)  Analysis and design methodologies developed by traffic and transportation engineers.  The following slides will show the basic method to calculate the

capacity of a roadway segment that is not influenced by at-grade intersection, entry or exit ramps or any other disturbance.  However, before doing so, it is important to define the concept of

highway Levels of Service.

“IDEAL” CONDITIONS IN THE HIGHWAY • Width Lateral and Space Lateral At ideal conditions, a roadway segment requires 3.6m (12 wide feet) lane width. Lateral obstructions are at least (1.8m) 6 feet from the pavement edge.

• Trucks/Busses and elevations In ideal conditions, the roads are flats and vehicular flow is only composed by small cars because large vehicles such as busses and trucks tend to give an adverse effect on the traffic flow.

“IDEAL” CONDITIONS IN THE HIGHWAY • Uniformity of demand: • For a road in ideal conditions, it is assumed that the flow is uniform throughout period of analysis. • If there were peaks of demand, this will cause problems that would take time to flow. • The typical period is 1 hour analysis. • Demand is quantify by using the terms of Volume (V) and Flow rate (q)

“IDEAL” CONDITIONS IN THE HIGHWAY • Uniformity of demand • Volume, V: number of vehicles passing a point on a road or highway line during one hour, expressed in vehicles per hour. • Flow rate, q: number of vehicles passing a point on a road or highway lane over a period of time less than one hour , expressed as a rate equivalent in vehicles per hour. Example: If 100 vehicles were counted for 5 minutes, the flow rate is equal to 100 veh / 5 min per 12 (5 min period) = 1200 veh/h

“IDEAL” CONDITIONS IN THE HIGHWAY

• Peak hour is defined as period of 60 minutes (1 hour) during daytime in which the road experiences the greatest amount of volume. • Peak hour Factor is the ratio between the volume during rush hour and the maximum flow calculated on the base of an interval of 15 minutes. PHF is a measure of uniformity of demand or peak of the demand.

EXAMPLE 1: UNIFORM DEMAND • Assume that 50 vehicles were counted during all periods with an interval of 5 minutes during rush hour. Calculate the PHF.

EXAMPLE 2: DEMAND WITH EXTREME PEAK • Assuming that during 5 minutes, 150 vehicles were measured and during the rest of the hour some vehicles were not measured. Calculate the PHF.

CAPACITY PEAK HOUR FACTOR (PHF) • First example shows if the traffic is uniform, then PHF is 1. • On the contrary, in an unreal case where all the traffic happens only in 5 minutes of the rush hour, then the PHF is 0.083 • For actual conditions, the PHF will be within those limits. • The closer to 1 – a more uniform traffic, • The closer to 0 - non-uniform traffic (extreme peak)

CAPACITY AND LEVELS OF HIGHWAYS SERVICE

The graphic shows the relationship between the speed and the flow rate per highway lane for several designs, defined by design speed and the number of available lanes under ideal conditions.

CAPACITY AND LEVELS OF HIGHWAYS SERVICE The figure shows that the capacity of the highway lane is around of: 2000 vehicles (passenger cars - pc) per hour (pc/h) per lane for speed design from 60 to 70 miles. 1900 vehicles for speed design of 50 miles.

LEVELS OF SERVICE • The q-k, v-q, q-k graphs vary with respect to the Safety Regime • Thus, depending on the regime, the traffic varies between free flow and conditions of severe congestion • To understand these conditions, the Highway Capacity Manual de 1965 (Manual de Capacidad Carretero de EEUU) included the term Levels of Service.

LEVEL OF SERVICE “A” • It represents Free Flow conditions. • Users are not affected by the presence of other vehicles in the vehicular flow. • The user can choose its speed. • The conformability and convenience of the drivers, passengers and pedestrians is excellent.

LEVEL OF SERVICE “B” • The flow is stable but the presence of other vehicles is starting to be noted.

• The speed can still be chosen without influence of adjacent vehicles, but there is a decrease in the freedom of maneuverability compared to level “A”. • Due to this present, the conformability and convenience of the drivers, passengers and pedestrians is slightly reduced.

LEVEL OF SERVICE “C” • The flow is still stable but at this point the presence of other vehicles affect the user behavior. • Driving through the vehicle flow requires total attention to the adjacent vehicles. • The

conformability and convenience levels are considerably reduced

LEVEL OF SERVICE “D” • The flow is still stable but it has a high density. • The speeds and freedom of maneuverability are severely restricted. • The conformability and convenience of the driver is very poor. Slight increments in traffic flow will generally produced operational problems at this level of service.

LEVEL OF SERVICE “E” • In these conditions, the road is either close or at its capacity and the speeds are slow but still uniform

• It is very difficult to have maneurability in the vehicular flow and normally they are obtained when a vehicle or a pedestrian provide space for maneuvers • The conformability and convenience levels are extremely poor and the operation at this level is unstable, and minor changes in the flow yield severe traffic jams.

LEVEL OF SERVICE “F” • At this level, the flow is severely congested. The traffic exceeds capacity. Queues are generated. • The operations are mostly Stop-and-Go and are highly unstable and the vehicles can move at reasonable speeds for some meters, but then they stop. This is repeated continuously.

• It is important to note that even when the condition is F, one the vehicle passes the traffic jam, the driver can experience better levels of service down the road.

FREEWAY AND HIGHWAY LOS

Outline 1. Definitions 2. Level of Service (LOS) 3. Freeway Segment LOS Determination a. Free-flow speed b. Flow Rate

4. Multilane Highway LOS 5. Design Traffic Volume

Freeway Defined • A divided highway with full control of access and two or more lanes for the exclusive use of traffic in each direction. • Assumptions • No interaction with adjacent facilities (streets, other freeways) • Free-flow conditions exist on either side of the facility being analyzed • Outside the influence or ramps and weaving areas

Basic Freeway Segment

From Highway Capacity Manual, 2000

Definitions • Freeway Capacity • The maximum sustained 15-min flow rate, expressed in passenger cars per hour per lane, that can be accommodated by a uniform freeway segment under prevailing traffic and roadway conditions in one direction of flow.

Definitions – Flow Characteristics • Undersaturated • Traffic flow that is unaffected by upstream or downstream conditions. • Queue discharge • Traffic flow that has just passed through a bottleneck and is accelerating back to the FFS of the freeway. • Oversaturated • Traffic flow that is influenced by the effects of a downstream bottleneck.

From Highway Capacity Manual, 2000

Speed vs. Flow Speed (mph)

Sf Free Flow Speed Uncongested Flow

Sm

Congested Flow

Optimal flow, capacity, vm

Flow (veh/hr)

Uncongested Flow

From Highway Capacity Manual, 2000

Definitions – Free-Flow Speed • Free-Flow Speed (FFS) • The mean speed of passenger cars that can be accommodated under low to moderate flow rates on a uniform freeway segment under prevailing roadway and traffic conditions.

• Factors affecting free-flow speed • • • • •

Lane width Lateral clearance Number of lanes Interchange density Geometric design

Definitions • Passenger car equivalents • Trucks and RVs behave differently • Baseline is a freeway with all passenger cars • Traffic is expressed in passenger cars per lane per hour (pc/ln/hr or pcplph)

• Driver population • Non-commuters fail more at driving • They may affect capacity

• Capacity • Corresponds to LOS E and v/c = 1.0

Definitions – Level of Service (LOS) • Chief measure of “quality of service” • Describes operational conditions within a traffic stream. • Does not include safety • Different measures for different facilities

• Six measures (A through F) • Freeway LOS • Based on traffic density

Levels of Service • Free-flow operation

• LOS B • Reasonably free flow • Ability to maneuver is only slightly restricted • Effects of minor incidents still easily absorbed

From Highway Capacity Manual, 2000

• LOS A

• LOS C • Speeds at or near FFS • Freedom to maneuver is noticeably restricted • Queues may form behind any significant blockage.

• LOS D • Speeds decline slightly with increasing flows • Density increases more quickly • Freedom to maneuver is more noticeably limited • Minor incidents create queuing

From Highway Capacity Manual, 2000

Levels of Service

• LOS E • • • •

Operation near or at capacity No usable gaps in the traffic stream Operations extremely volatile Any disruption causes queuing

• LOS F • Breakdown in flow • Queues form behind breakdown points • Demand > capacity

From Highway Capacity Manual, 2000

Levels of Service

Freeway LOS

LOS Calculation • Does not consider • Special lanes reserved for a particular type of vehicle (HOV, truck, climbing, etc.) • Extended bridge and tunnel segments • Segments near to a toll plaza • Facilities with FFS < 55 mi/h or > 75 mi/h • Demand conditions in excess of capacity • Influence of downstream blockages or queuing • Posted speed limit • Intelligent transportation system features • Capacity-enhancing effects of ramp metering

Input Geometric Data Measured FFS or BFFS Volume BFFS Input

BFFS Adjustment Lane width Number of lanes Interchange density Lateral clearance

Measured FFS Input

Compute FFS

Volume Adjustment PHF Number of lanes Driver population Heavy vehicles

Compute flow rate

Define speed-flow curve

Compute density using flow rate and speed

Determine speed using speed-flow curve

Determine LOS

From Highway Capacity Manual, 2000

LOS Criteria for Basic Freeway Segments

Determining FFS • Measure FFS in the field • Low to moderate traffic conditions

• Use a baseline and adjust it (BFFS)

FFS = BFFS − f LW − f LC − f N − f ID FFS = free-flow speed (mph) BFFS = base free-flow speed, 70 mph (urban), 75 mph (rural) fLW = adjustment for lane width (mph) fLC = adjustment for right-shoulder lateral clearance (mph) fN = adjustment for number of lanes (mph) fID = adjustment for interchange density (mph)

Lane Width Adjustment (fLW) • Base condition (fLW = 0)

• Average width of 12 ft. or wider across all lanes

From Highway Capacity Manual, 2000

Lateral Clearance Adjustment (fLC) • Base condition (fLC = 0)

• 6 ft. or greater on right side • 2 ft. or greater on the median or left side

From Highway Capacity Manual, 2000

Number of Lanes Adjustment (fN) • Base condition (fN = 0)

• 5 or more lanes in one direction • Do not include HOV lanes • fN = 0 for all rural freeway segments

From Highway Capacity Manual, 2000

Interchange Density Adjustment (fIC) • Base condition (fIC = 0)

• 0.5 interchanges per mile (2-mile spacing) • Interchange defined as having at least one on-ramp • Determined over 6-mile segment

From Highway Capacity Manual, 2000

Determining Flow Rate • Adjust hourly volumes to get pc/ln/hr

V vp = PHF  N  f HV  f p vp = 15-minute passenger-car equivalent flow rate (pcphpl) V = hourly volume (veh/hr) PHF = peak hour factor N = number of lanes in one direction fHV = heavy-vehicle adjustment factor fP = driver population adjustment factor

Peak Hour Factor (PHF) • Typical values • 0.80 to 0.95 • Lower PHF characteristic or rural or off-peak • Higher PHF typical of urban peak-hour

V PHF = V15  4 V = hourly volume (veh/hr) for hour of analysis V15 = maxiumum 15-min. flow rate within hour of analysis 4 = Number of 15-min. periods per hour

Heavy Vehicle Adjustment (fHV) • Base condition (fHV = 1.0)

• No heavy vehicles • Heavy vehicle = trucks, buses, RVs

• Two-step process • Determine passenger-car equivalents (ET) • Determine fHV

Determine fHV f HV

1 = 1 + PT (ET − 1) + PR (ER − 1)

fHV = Heavy vehicle adjustment factor ET, ER = Passenger-car equivalents for trucks/buses and RVs

PT, PR = Proportion of trucks/buses and RVs in traffic stream

Passenger-Car Equivalents (ET) • Extended segments method • Determine the type of terrain and select ET • No one grade of 3% or more is longer than 0.25 miles OR • No one grade of less than 3% is longer than 0.5 miles

From Highway Capacity Manual, 2000

Passenger-Car Equivalents (ET) • Specific grades method • Any grade of 3% or more that is longer than 0.25 miles OR • Any grade of less than 3% that is longer than 0.5 miles

From Highway Capacity Manual, 2000

From Highway Capacity Manual, 2000

Passenger-Car Equivalents (ET)

Passenger-Car Equivalents (ET) • Composite grades method • Determines the effect of a series of steep grades in succession • Method OK if… • All subsection grades are less than 4% OR • Total length of composite grade is less than 4000 ft.

• Otherwise, use a detailed technique in the Highway Capacity Manual (HCM)

From Highway Capacity Manual, 2000

Determine fHV f HV

1 = 1 + PT (ET − 1) + PR (ER − 1)

fHV = Heavy vehicle adjustment factor

ET, ER = Passenger-car equivalents for trucks/buses and RVs PT, PR = Proportion of trucks/buses and RVs in traffic stream

Driver Population Adjustment (fP) • Base condition (fP = 1.0)

• Most drivers are familiar with the route • Commuter drivers

• Typical values between 0.85 and 1.00

• Two-step process • Determine passenger-car equivalents (ET) • Determine fHV

Define Speed-Flow Curve Select a Speed-Flow curve based on FFS

From Highway Capacity Manual, 2000

Determine Average PC Speed (S) Use vp and FFS curve to find average passenger car speed (S)

From Highway Capacity Manual, 2000

Determine Average PC Speed (S) For 70 < FFS ≤ 75 mph AND (3400 – 30FFS) < vp ≤ 2400 2.6   v + 30 FFS − 3400   160  p   S = FFS −  FFS −  3  30FFS − 1000    

For 55 < FFS ≤ 70 mph AND (3400 – 30FFS) < vp ≤ (1700 + 10FFS) 2.6 1  v p + 30FFS − 3400     S = FFS −  (7 FFS − 340)  9  40FFS − 1700  

For 55 < FFS ≤ 75 mph AND vp < (3400 – 30FFS)

S = FFS

Determine Density • Calculate density using:

D=

vp S

D = density (pc/mi/ln) vp = flow rate (pc/hr/ln) S = average passenger-car speed (mph)

From Highway Capacity Manual, 2000

LOS Criteria for Basic Freeway Segments

Determine LOS

Example Determine the typical LOS for a three lanes highways at 7 a.m. (4000vph) and 10 p.m. (1700vph) Geometry • 11 ft. lane width • Left lateral clearance = 5 ft. • Right lateral clearance = 4 ft. Other • 7 am PHF = 0.95 • 10 pm PHF = 0.99 • 2% trucks • 3% buses • Assume BFFS=70mph • 0.5 interchange per mile • Assume no RVs and commuters

Determine FFS

Determine FFS

Determine fID

Determine FFS

Determine Flow Rate (vp)

Determine LOS

From Highway Capacity Manual, 2000

LOS Criteria for Basic Freeway Segments

LOS EXERCISES

EXAMPLE 1 • In a future highway is expected a demand of 3,000 veh/h, where 12% will be trucks, 5% busses and 0% recreational vehicles. • Determine the minimum number of lanes needed on the highway to provide a level of service C, knowing that: • • • • •

PHF = 0.80 The ground is slightly inclined (rolling) Design speed = 70 mph Lane width = 12 feet The road will have appropriate lateral spaces

EXAMPLE 2 • A flat highway has a volume V = 4500 veh/h in 4 lanes of 11 feet per direction. • The combination of vehicles consists of 75% private cars, 10% trucks, 10% busses y 5% recreational vehicles. • Obstruction sides are 5 feet to the right and 3 feet to the left of the roadway. • If the design speed is 60 mph and the PHF = 0.75 • Calculate the level of service level and the ratio v/c

EXERCISE • A 6-lane highway is used by 3500 veh/h in the peak direction. This volume is composed by 10% trucks and 90% private vehicles. • The ground is slightly inclined. • The design speed is 60 mph. • Beyond that, all other conditions are ideal. • If the peak count in 5 min is 350 vehicles, calculate: • Road capacity in one direction • Level of Service under given conditions • Average speed under given conditions

CONCLUSIONS 01

Is the job of the Transportation Engineer to determine the existing conditions of the roadways and anticipate future operational conditions, in order to provide countermeasures and enhance the quality of the transportation service.

02

To measure existing and future conditions is necessary to determine the LEVEL OF SERVICE of the highways. The Highway Capacity Manual (HCM) considers six levels of service, from A to F, being A the best condition and F the worst.

REFERENCES ▪ Mannering, F.L.; Kilareski, W.P. and Washburn, S.S. (2003). Principles of Highway Engineering and Traffic Analysis, Third Edition (Draft). Chapter 5

▪ Transportation Research Board. (2000). Highway Capacity Manual 2000. National Research Council, Washington, D.C.