CEE 320 Spring 2008 Level of Service and

CEE 320 Spring 2008 Level of Service and Design Traffic Volumes CEE 320 Kelly Pitera

Outline 1. Freeway Segment LOS Determination a. Free-flow speed b. Flow Rate CEE 320 Spring 2008 2. Multilane Highway LOS 3. Design Traffic Volume

CEE 320 Spring 2008 Freeway LOS

Freeway LOS Calculation • Does not consider CEE 320 Spring 2008 – Special lanes reserved for a particular type of vehicle (HOV, truck, climbing, etc. ) – Extended bridge and tunnel segments – Segments near 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 – Extent of police enforcement – Intelligent transportation system features – Capacity-enhancing effects of ramp metering

Freeway LOS Input Geometric Data Measured FFS or BFFS Volume (highest) BFFS Input If FFS not known BFFS Adjustment Lane width Number of lanes Interchange density Lateral clearance Measured FFS Input Volume Adjustment PHF Number of lanes Driver population Heavy vehicles Compute FFS Compute flow rate Determine S from speed-flow curve Compute density using flow rate and speed CEE 320 Spring 2008 Determine LOS Check on speed-flow curve Adjust for temporal variation

Freeway LOS Determining FFS • Measure FFS in the field – Low to moderate traffic conditions • Use a baseline and adjust it (BFFS) FFS = free-flow speed (mph) BFFS = base free-flow speed, 70 mph (urban), 75 mph (rural) f. LW = adjustment for lane width (mph) CEE 320 Spring 2008 f. LC = adjustment for right-shoulder lateral clearance (mph) f. N = adjustment for number of lanes (mph) f. ID = adjustment for interchange density (mph)

Base conditions for basic freeway segment CEE 320 Spring 2008 • • 12 -ft lane widths 6 -ft right shoulder 2 -ft median lateral clearance Only passenger cars 5 or more lanes in each travel direction 2 -mi or greater interchange spacing Level terrain Mostly familiar roadway users

Freeway LOS Lane Width Adjustment (f. LW) • Base condition (f. LW = 0) – Average width of 12 ft. or wider across all lanes CEE 320 Spring 2008 – Table 6. 3 in text From Highway Capacity Manual, 2000

Freeway LOS Lateral Clearance Adjustment (f. LC) • Base condition (f. LC = 0) CEE 320 Spring 2008 – 6 ft. or greater on right side – 2 ft. or greater on the median or left side – Table 6. 4 in text From Highway Capacity Manual, 2000

Freeway LOS Number of Lanes Adjustment (f. N) • Base condition (f. N = 0) CEE 320 Spring 2008 – 5 or more lanes in one direction – Do not include HOV lanes – f. N = 0 for all rural freeway segments – Table 6. 5 in text From Highway Capacity Manual, 2000

Freeway LOS Interchange Density Adjustment (f. ID) • Base condition (f. ID = 0) CEE 320 Spring 2008 – 0. 5 interchanges per mile (2 -mile spacing) – Interchange defined as having at least one on-ramp – Determined over 6 -mile segment – Table 6. 6 in text From Highway Capacity Manual, 2000

Freeway LOS Determining FFS • Use a baseline and adjust it (BFFS) FFS = free-flow speed (mph) BFFS = base free-flow speed, 70 mph (urban), 75 mph (rural) f. LW = adjustment for lane width (mph) f. LC = adjustment for right-shoulder lateral clearance (mph) f. N = adjustment for number of lanes (mph) CEE 320 Spring 2008 f. ID = adjustment for interchange density (mph)

Freeway LOS Input Geometric Data Measured FFS or BFFS Volume (highest) BFFS Input If FFS not known BFFS Adjustment Lane width Number of lanes Interchange density Lateral clearance Measured FFS Input Volume Adjustment PHF Number of lanes Driver population Heavy vehicles Compute FFS Compute flow rate Determine S from speed-flow curve Compute density using flow rate and speed CEE 320 Spring 2008 Determine LOS Check on speed-flow curve Adjust for temporal variation

Freeway LOS Determining Analysis Flow Rate • Adjust hourly volumes to get pc/ln/hr vp = 15 -minute passenger-car equivalent flow rate (pcphpl) V = hourly volume (veh/hr) highest, total one direction PHF = peak hour factor CEE 320 Spring 2008 N = number of lanes in one direction f. HV = heavy-vehicle adjustment factor f. P = driver population adjustment factor

Freeway LOS Peak Hour Factor (PHF) • Typical values – 0. 80 to 0. 95 – Lower PHF characteristic of rural or off-peak – Higher PHF typical of urban peak-hour V = hourly volume (veh/hr) for hour of analysis CEE 320 Spring 2008 V 15 = maximum 15 -min. flow rate within hour of analysis 4 = Number of 15 -min. periods per hour

Freeway LOS Heavy Vehicle Adjustment (f. HV) • Base condition (f. HV = 1. 0) – No heavy vehicles – Heavy vehicle = trucks, buses, RVs • Two-step process CEE 320 Spring 2008 – Determine passenger-car equivalents (ET, ER) for this traffic stream – Determine f. HV

Freeway LOS Passenger-Car Equivalents (ET, ER) • Extended segments method – Determine the type of terrain and select ET, ER • Level, rolling, mountainous CEE 320 Spring 2008 – 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 – Table 6. 7 in text From Highway Capacity Manual, 2000

Freeway LOS Passenger-Car Equivalents (ET) • Specific grades method CEE 320 Spring 2008 – 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 Freeway LOS

Freeway LOS CEE 320 Spring 2008 Passenger-Car Equivalents (ER)

Freeway LOS Passenger-Car Equivalents (ET, ER) • Composite grades method – Determines the effect of a series of steep grades in succession – Distance weighted average – Method OK if… • All subsection grades are less than 4% OR • Total length of composite grade is less than 4000 ft. CEE 320 Spring 2008 – Otherwise, use a detailed technique in the Highway Capacity Manual (HCM) From Highway Capacity Manual, 2000

Freeway LOS Determine f. HV = Heavy vehicle adjustment factor ET, ER = Passenger-car equivalents for trucks/buses and RVs CEE 320 Spring 2008 PT, PR = Proportion of trucks/buses and RVs in traffic stream

Freeway LOS Driver Population Adjustment (f. P) • Base condition (f. P = 1. 0) – Most drivers are familiar with the route • Commuter drivers • Typical values between 0. 85 and 1. 00 CEE 320 Spring 2008 – Analyst selects the value using judgement – Dependent on local conditions (scenic views, etc. )

Freeway LOS Determining Analysis Flow Rate • Adjust hourly volumes to get pc/ln/hr vp = 15 -minute passenger-car equivalent flow rate (pcphpl) V = hourly volume (veh/hr) highest, total one direction PHF = peak hour factor CEE 320 Spring 2008 N = number of lanes in one direction f. HV = heavy-vehicle adjustment factor f. P = driver population adjustment factor

Freeway LOS Input Geometric Data Measured FFS or BFFS Volume (highest) BFFS Input If FFS not known BFFS Adjustment Lane width Number of lanes Interchange density Lateral clearance Measured FFS Input Volume Adjustment PHF Number of lanes Driver population Heavy vehicles Compute FFS Compute flow rate Determine S from speed-flow curve Compute density using flow rate and speed CEE 320 Spring 2008 Determine LOS Check on speed-flow curve Adjust for temporal variation

Freeway LOS Define Speed-Flow Curve CEE 320 Spring 2008 Select a Speed-Flow curve based on FFS From Highway Capacity Manual, 2000

Freeway LOS Determine Average PC Speed (S) For 70 < FFS ≤ 75 mph AND (3400 – 30 FFS) < vp ≤ 2400 For 55 < FFS ≤ 70 mph AND (3400 – 30 FFS) < vp ≤ (1700 + 10 FFS) CEE 320 Spring 2008 For 55 < FFS ≤ 75 mph AND vp < (3400 – 30 FFS)

Freeway LOS Input Geometric Data Measured FFS or BFFS Volume (highest) BFFS Input If FFS not known BFFS Adjustment Lane width Number of lanes Interchange density Lateral clearance Measured FFS Input Volume Adjustment PHF Number of lanes Driver population Heavy vehicles Compute FFS Compute flow rate Determine S from speed-flow curve Compute density using flow rate and speed CEE 320 Spring 2008 Determine LOS Check on speed-flow curve Adjust for temporal variation

Freeway LOS Determine Density • Calculate density using: D = density (pc/mi/ln) vp = flow rate (pc/hr/ln) CEE 320 Spring 2008 S = average passenger-car speed (mph)

From Highway Capacity Manual, 2000 LOS Criteria for Basic Freeway Segments CEE 320 Spring 2008 Freeway LOS Determine LOS

Freeway LOS Define Speed-Flow Curve CEE 320 Spring 2008 Select a Speed-Flow curve based on FFS From Highway Capacity Manual, 2000

Freeway LOS Example Determine the typical LOS for a 6 mile stretch of roadway with 5 interchanges. Geometry • 11 ft. lane width • 2 lanes • Left lateral clearance = 5 ft. • Right lateral clearance = 4 ft. CEE 320 Spring 2008 Other • SR 520 • 7 am PHF = 0. 95 • 2% trucks • 3% buses Determine free flow speed, analysis flow rate

Freeway LOS Determine FFS (f. LW) CEE 320 Spring 2008 • • FFS = BFFS – f. LW – f. LC – f. N – f. ID BFFS is 70 mph for urban freeway Given 11 ft lanes f. LW = 1. 9

Freeway LOS Determine FFS (f. LC ) CEE 320 Spring 2008 • FFS = BFFS – f. LW – f. LC – f. N – f. ID • Given 2 lanes, 4 ft right clr • f. LC = 1. 2

Freeway LOS Determine FFS (f. N) CEE 320 Spring 2008 • FFS = BFFS – f. LW – f. LC – f. N – f. ID • Given: 2 lanes • f. N = 4. 5

Freeway LOS Determine FFS (f. ID) • FFS = BFFS – f. LW – f. LC – f. N – f. ID • f. ID = 2. 1 CEE 320 Spring 2008 In a 6 -mile stretch there are 5 interchanges 5/6=. 833 Linear interpolation: (1 -. 75)/(1 -0. 833)=(2. 5 -1. 3)/(2. 5 -x); x = 2. 05

Determine FFS CEE 320 Spring 2008 • FFS = BFFS – f. LW – f. LC – f. N – f. ID • FFS = 70 – 1. 9 – 1. 2 – 4. 5 – 2. 1 = 60. 3 mph

Freeway LOS Example Determine the typical LOS the a 6 mile stretch of roadway with 5 interchanges. Geometry • 11 ft. lane width • 2 lanes • Left lateral clearance = 5 ft. • Right lateral clearance = 4 ft. CEE 320 Spring 2008 Other • SR 520 • 7 am PHF = 0. 95 • 2% trucks • 3% buses FFS = 60. 3 mph

Freeway LOS CEE 320 Spring 2008 Determine Flow Rate (V) At 7 am the ½ hour volume is about 4000 veh/hr Assume half in each direction, 4000 veh/hr max Graph from the Puget Sound Regional Council’s Puget Sound Trends, No. T 6, July 1997

Freeway LOS Determine Flow Rate (vp) • ET = 1. 5, ER = 1. 2 • Assume there are no RVs CEE 320 Spring 2008 • f. HV = 1/(1+PT(ET-1) + PR(ER-1) • f. HV = 1/(1+0. 05(1. 5 -1) + 0(1. 2 -1) = 0. 9756 • Assume commuters, therefore f. P = 1. 00 • Vp = V/ (PHF*N*f. HV*f. P) • Vp = 4000 vph / (0. 95)(2)(0. 9756)(1. 00) = 2158 pcplph

Freeway LOS CEE 320 Spring 2008 Determine LOS FFS = 60 mph, Vp = 2158 pcplph, S = about 56 mph, Looks like LOS E, Density = 2158/56 = 39 pc/mi/ln

LOS Criteria for Basic Freeway Segments From Highway Capacity Manual, 2000 CEE 320 Spring 2008 Freeway LOS

CEE 320 Spring 2008 Multilane Highway LOS

Multilane Highway LOS CEE 320 Spring 2008 • Similar to Freeway LOS • A few minor differences

Multilane Highway LOS Free Flow Speed (FFS) • Measure FFS in the field – Low to moderate traffic conditions • Use a baseline and adjust it (BFFS) FFS = free-flow speed (mph) BFFS = base free-flow speed, 60 mph is typically used f. LW = adjustment for lane width (mph) CEE 320 Spring 2008 f. LC = adjustment for lateral clearance (mph) f. M = adjustment for median type (mph) f. A = adjustment for access points (mph)

Multilane Highway LOS Base Conditions for Multilane Highway CEE 320 Spring 2008 • Level terrain, with grades no greater than 2 percent • Minimum lane width = 12 ft • Objects no closer than 6 ft from the edge of the traveled pavement (at the roadside or median) • No direct access points along the roadway • Divided highway • Traffic stream composed entirely of passenger cars • Free flow speed of 60 mph or more • Driver population composed principally of regular users

Multilane Highway LOS Lane Width Adjustment (f. LW) • Base condition (f. LW = 0) – Average width of 12 ft. or wider across all lanes CEE 320 Spring 2008 Same as Freeway LOS From Highway Capacity Manual, 2000

Multilane Highway LOS Lateral Clearance Adjustment (f. LC) • Base condition (f. LC = 0) – 12 ft or greater TLC • LCL = 6 ft for undivided highways – (accounted for in median type adjustment) From Highway Capacity Manual, 2000 CEE 320 Spring 2008 • LCL = 6 ft for two-way left-turn lanes

Multilane Highway LOS Median Adjustment (f. M) • Base condition (f. M = 0) CEE 320 Spring 2008 – Divided highway From Highway Capacity Manual, 2000

Multilane Highway LOS Access-Point Density Adjustment (f. A) • For each access point/mi FFS decreases by 0. 25 mph • Base condition (f. A = 0) – 0 access points per mile CEE 320 Spring 2008 • For NAPM ≤ 40: f. A = 0. 25 × NAPM • For NAPM > 40: f. A = 10 From Highway Capacity Manual, 2000

Multilane Highway LOS Determining Flow Rate • Adjust hourly volumes to get pc/ln/hr vp = 15 -minute passenger-car equivalent flow rate (pcphpl) V = hourly volume (veh/hr) PHF = peak hour factor CEE 320 Spring 2008 N = number of lanes in one direction f. HV = heavy-vehicle adjustment factor f. P = driver population adjustment factor Same as Freeway LOS

Multilane Highway LOS Passenger-Car Equivalents (ET) • Extended segments method CEE 320 Spring 2008 – Determine the type of terrain and select ET – No one grade of 3% or more is longer than 0. 5 miles OR – No one grade of less than 3% is longer than 1 mile From Highway Capacity Manual, 2000

Multilane Highway LOS Passenger-Car Equivalents (ET) • Specific grades method CEE 320 Spring 2008 – Any grade of 3% or more that is longer than 0. 5 miles OR – Any grade of less than 3% that is longer than 1 mile From Highway Capacity Manual, 2000

Multilane Highway LOS Determine Average PC Speed (S) CEE 320 Spring 2008 Use vp and FFS curve to find average passenger car speed (S) From Highway Capacity Manual, 2000

Multilane Highway LOS From Highway Capacity Manual, 2000 CEE 320 Spring 2008 LOS Criteria for Multilane Highways

CEE 320 Spring 2008 Design Traffic Volumes

Design Traffic Volumes CEE 320 Spring 2008 • Need to select the appropriate hourly traffic volume to get the design LOS

Definitions • Annual average daily traffic (AADT) – Annual traffic averaged on a daily basis • Design hourly volume (DHV) – Traffic volume used for design calculations – Typically between the 10 th and 50 th highest volume hour of the year (30 th highest is most common) • K-factor CEE 320 Spring 2008 – Relationship between AADT and DHV

Definitions • Directional distribution factor (D) – Factor reflecting the proportion of peak-hour traffic traveling in the peak direction – Often there is much more traffic in one direction than the other CEE 320 Spring 2008 • Directional design-hour volume (DDHV)

CEE 320 Spring 2008 Hourly volume as a proportion of AADT Typical Graph Highest 100 Hourly Volumes Over a One-Year Period for a Typical Roadway 0. 15 0. 14 K 30=0. 12 0. 13 0. 12 0. 11 0. 10 0 20 40 60 80 Number of hours (annually) with specified or greater volumes 100

Example • Freeway • PC only facility • AADT = 35, 000 veh/day • FFS = 70 mph • Commuters • D = 65% (PH traffic in peak dir. ) • PHF=0. 85 CEE 320 Spring 2008 Number of lanes required to provide at least LOS C using the 30 th highest annual hourly volume?

Example CEE 320 Spring 2008 K = 0. 12 (graph) D = 0. 65 (given) AADT = 35, 000 (given)

Example CEE 320 Spring 2008 V = 2730 (previous slide) PHF = 0. 85 (given) N = 2 (assume 4 -lane freeway) f. HV = 1. 0 f. P = 1. 0 From Table 6. 1 in text, maximum flow rate for FSS = 70 mph and LOS C is 1770 pc/h/lane. 1606 pc/h/lane < 1770 pc/h/lane, therefore 4 -lane freeway (2 lanes each direction) is okay.