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Reliability and Quality of Service Evaluation Methods for Rural Highways: A Guide (2024)

Chapter: 6 Multilane Highway Segment Analysis Methodology

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Previous Chapter: 5 HCM7 Automobile LOS Methodologies

Page 71

Suggested Citation: "6 Multilane Highway Segment Analysis Methodology." National Academies of Sciences, Engineering, and Medicine. 2024. Reliability and Quality of Service Evaluation Methods for Rural Highways: A Guide. Washington, DC: The National Academies Press. doi: 10.17226/27895.

CHAPTER 6 Multilane Highway Segment Analysis Methodology

The core multilane highway analysis methodology is contained in HCM7 Chapter 12, Basic Freeway and Multilane Highway Segments. While this chapter also covers basic freeway segments, such segments are not included in the rural highway analysis methodology.

The motorized vehicle analysis methodology process is given in HCM7 Exhibit 12-19 (p. 12-26). The specific equation and exhibit numbers used in the methodology (multilane highway only), in the general order in which they are applied, are as follows.

6.1 Equations and Exhibits

The variable definitions for these equations are shown in Section 6.2 Nomenclature.

Step 1: Input Data

No applicable equations or exhibits.

Step 2: Estimate and Adjust FFS

The following HCM7 equations apply only to FFS estimation. There are no applicable equations or exhibits for measured FFS, as this is a direct user input.

Equation 12-3: FFS estimation; uses results from Equation 12-4 and Exhibits 12-20, 12-22, 12-23, 12-24.
FFS = BFFS − f_LW − f_TLC − f_M − f_A (HCM7 Eq. 12-3)

Exhibit 12-20: Adjustment to FFS for average lane width.

Lane width (ft)	*Reduction in FFS, f_LW* (mi/h)**
12	0.0
11	1.9
10	6.6

Equation 12-4: Total lateral clearance for use with Exhibit 12-22.
TLC = LC_R + LC_L (HCM7 Eq. 12-4)

The maximum value for LC_R and LC_L is 6 ft. Thus, the maximum value for TLC is 12 ft.

Page 72

Exhibit 12-22: Adjustment to FFS for lateral clearance.

Total lateral clearance (ft)	Reduction in FFS, f_TLC (mi/h), four-lane highways	Total lateral clearance (ft)	Reduction in FFS, f_TLC (mi/h), six-lane highways
12	0.0	12	0.0
10	0.4	10	0.4
8	0.9	8	0.9
6	1.3	6	1.3
4	1.8	4	1.7
2	3.6	2	2.8
0	5.4	0	3.9

Exhibit 12-23: Adjustment to FFS for median type.

Median type	Reduction in FFS, (mi/h)
Undivided highways	1.6
Divided highways (including TWLTLs)	0

Exhibit 12-24: Adjustment to FFS for access point density.

Access points/mile	Reduction in FFS, fA (mi/h)
0	0.0
10	2.5
20	5.0
30	7.5
40	10.0

Step 3: Estimate and Adjust Capacity

Equation 12-7: Capacity estimation; uses result from Equation 12-3.

c = Min [1, 900 + 20 (F F S_{a d j} - 45), 2, 300] 45 \leq F F S \leq 70

(HCM7 Eq. 12-7)

Step 4: Adjust Demand Volume

Equation 12-9: Analysis flow rate estimation; uses results from Equations 4-2 and 12-10, and Exhibits 12-25–12-28.

v_{p} = \frac{V}{P H F \times N \times F_{H V}}

(HCM7 Eq. 12-9)

Equation 4-2: Peak hour factor (PHF); in HCM7 Chapter 4, Traffic Operations and Capacity Concepts.

P H F = \frac{V}{V_{15} \times 4}

(HCM7 Eq. 4-2)

Equation 12-10: Heavy-vehicle adjustment factor.

f_{H V} = \frac{1}{1 + P_{T} (E_{T} - 1)}

(HCM7 Eq. 12-10)

Page 73

Methodology Simplification

Current “level” and “rolling” terrain guidelines will apply; for steeper/longer grades, only the specific grade approach will be applied—the “mixed flow” model will not be applied because of its complexity; when there are consecutive grades that should be analyzed with the specific grade approach, the following guidance applies: If the individual grades are less than or equal to 0.5 miles, they are combined into a single segment and the highest grade percentage is applied over the entire length. If a grade is longer than 0.5 miles, it is treated as an individual segment.

Exhibit 12-25: Passenger car equivalents (PCEs) for general terrain segments.

General Terrain

Terrain	ET
Level	2.0
Rolling	3.0

Specific Grades

When the analysis segment consists of terrain that cannot be considered as an extended general segment (i.e., level, rolling), Exhibits 12-26, 12-27, and 12-28 can be used to determine PCE values for specific upgrades and/or downgrades.

Exhibit 12-26: Passenger car equivalents (E_T) for heavy vehicles [30% single-unit trucks (SUTs)/70% tractor-trailers (TTs)] on specific grades.

Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
≤ 0	≤ 0.125	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.375	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.625	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.875	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	1.25	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	≥ 1.5	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97

Page 74

Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
2	≤ 0.125	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.375	3.76	2.96	2.78	2.65	2.48	2.38	2.22	2.14	2.09
	0.625	4.47	3.33	3.08	2.91	2.68	2.54	2.34	2.23	2.17
	0.875	4.8	3.5	3.22	3.03	2.77	2.61	2.39	2.28	2.21
	1.25	5	3.6	3.3	3.09	2.83	2.66	2.42	2.3	2.23
	≥ 1.5	5.04	3.62	3.32	3.11	2.84	2.67	2.43	2.31	2.23
2.5	≤ 0.125	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.375	4.11	3.14	2.93	2.78	2.58	2.46	2.28	2.19	2.13
	0.625	5.04	3.62	3.32	3.11	2.84	2.67	2.43	2.31	2.23
	0.875	5.48	3.85	3.51	3.27	2.96	2.77	2.5	2.36	2.28
	1.25	5.73	3.98	3.61	3.36	3.03	2.83	2.54	2.4	2.31
	≥ 1.5	5.8	4.02	3.64	3.38	3.05	2.84	2.55	2.41	2.32
3.5	≤ 0.125	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.375	4.88	3.54	3.25	3.05	2.8	2.63	2.41	2.29	2.22
	0.625	6.34	4.3	3.87	3.58	3.2	2.97	2.64	2.48	2.38
	0.875	7.03	4.66	4.16	3.83	3.39	3.12	2.76	2.57	2.46
	1.25	7.44	4.87	4.33	3.97	3.5	3.22	2.82	2.62	2.5
	≥ 1.5	7.53	4.92	4.38	4.01	3.53	3.24	2.84	2.63	2.51
4.5	≤ 0.125	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.375	5.8	4.02	3.64	3.38	3.05	2.84	2.55	2.41	2.32
	0.625	7.9	5.11	4.53	4.14	3.63	3.32	2.9	2.68	2.55
	0.875	8.91	5.64	4.96	4.5	3.92	3.56	3.07	2.82	2.67
	≥ 1.0	9.19	5.78	5.08	4.6	3.99	3.62	3.11	2.85	2.7

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Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
5.5	≤ 0.125	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.375	6.87	4.58	4.1	3.77	3.35	3.09	2.73	2.55	2.44
	0.625	9.78	6.09	5.33	4.82	4.16	3.76	3.21	2.93	2.77
	0.875	11.2	6.83	5.94	5.33	4.56	4.09	3.45	3.12	2.93
	≥ 1.0	11.6	7.04	6.11	5.47	4.67	4.18	3.51	3.17	2.97
≥ 6	≤ 0.125	2.62	2.37	2.3	2.24	2.17	2.12	2.04	1.99	1.97
	0.375	7.48	4.9	4.36	3.99	3.52	3.23	2.83	2.63	2.51
	0.625	10.87	6.66	5.79	5.21	4.46	4.01	3.39	3.08	2.89
	0.875	12.54	7.54	6.51	5.81	4.94	4.4	3.67	3.3	3.08
	≥ 1.0	13.02	7.78	6.71	5.99	5.07	4.51	3.75	3.37	3.14

Exhibit 12-27: Passenger car equivalents (E_T) for heavy vehicles (50% SUTs/50% TTs) on specific grades.

Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
≤ 0	≤ 0.125	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.375	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.625	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.875	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	1.25	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	≥ 1.5	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
2	≤ 0.125	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.375	3.76	2.95	2.77	2.64	2.47	2.36	2.2	2.11	2.06
	0.625	4.32	3.24	3.01	2.84	2.63	2.49	2.29	2.19	2.12
	0.875	4.57	3.37	3.11	2.93	2.7	2.55	2.33	2.22	2.15
	1.25	4.71	3.45	3.17	2.99	2.74	2.58	2.36	2.24	2.17
	≥ 1.5	4.74	3.47	3.19	3	2.75	2.59	2.36	2.24	2.17

Page 76

Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
2.5	≤ 0.125	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.375	4.1	3.13	2.92	2.77	2.57	2.44	2.26	2.16	2.1
	0.625	4.84	3.52	3.23	3.03	2.77	2.61	2.38	2.26	2.18
	0.875	5.17	3.69	3.37	3.15	2.87	2.69	2.43	2.3	2.22
	1.25	5.36	3.79	3.45	3.22	2.92	2.73	2.47	2.33	2.24
	≥ 1.5	5.4	3.81	3.47	3.24	2.93	2.74	2.47	2.33	2.25
3.5	≤ 0.125	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.375	4.89	3.54	3.25	3.05	2.79	2.62	2.39	2.26	2.19
	0.625	6.05	4.15	3.75	3.47	3.11	2.89	2.58	2.42	2.32
	0.875	6.58	4.43	3.97	3.66	3.26	3.01	2.67	2.49	2.39
	1.25	6.88	4.58	4.1	3.77	3.35	3.09	2.72	2.53	2.42
	≥ 1.5	6.95	4.62	4.13	3.8	3.37	3.1	2.73	2.54	2.43
4.5	≤ 0.125	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.375	5.83	4.03	3.65	3.39	3.05	2.84	2.55	2.39	2.3
	0.625	7.53	4.92	4.38	4.01	3.53	3.24	2.83	2.62	2.5
	0.875	8.32	5.34	4.72	4.29	3.75	3.42	2.97	2.73	2.59
	≥ 1.0	8.53	5.45	4.81	4.37	3.81	3.47	3	2.76	2.62
5.5	≤ 0.125	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.375	6.97	4.63	4.14	3.81	3.38	3.11	2.74	2.55	2.43
	0.625	9.37	5.89	5.16	4.68	4.05	3.67	3.14	2.88	2.72
	0.875	10.49	6.48	5.65	5.09	4.37	3.93	3.34	3.03	2.85
	≥ 1.0	10.8	6.64	5.78	5.2	4.46	4.01	3.39	3.08	2.89

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Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
≥ 6	≤ 0.125	2.67	2.38	2.31	2.25	2.16	2.11	2.02	1.97	1.93
	0.375	7.64	4.98	4.43	4.05	3.56	3.26	2.85	2.64	2.51
	0.625	10.45	6.45	5.63	5.07	4.36	3.92	3.33	3.03	2.85
	0.875	11.78	7.16	6.2	5.56	4.74	4.24	3.56	3.22	3.01
	≥ 1.0	12.15	7.35	6.36	5.69	4.85	4.33	3.62	3.27	3.05

Exhibit 12-28: Passenger car equivalents (E_T) for heavy vehicles (70% SUTs/30% TTs) on specific grades.

Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
≤ 0	≤ 0.125	2.39	2.18	2.12	2.07	2.01	1.96	1.89	1.85	1.83
	0.375	2.39	2.18	2.12	2.07	2.01	1.96	1.89	1.85	1.83
	0.625	2.39	2.18	2.12	2.07	2.01	1.96	1.89	1.85	1.83
	0.875	2.39	2.18	2.12	2.07	2.01	1.96	1.89	1.85	1.83
	1.25	2.39	2.18	2.12	2.07	2.01	1.96	1.89	1.85	1.83
	≥ 1.5	2.39	2.18	2.12	2.07	2.01	1.96	1.89	1.85	1.83
2	≤ 0.125	2.67	2.32	2.23	2.17	2.08	2.03	1.94	1.89	1.86
	0.375	3.63	2.82	2.64	2.52	2.35	2.25	2.1	2.02	1.97
	0.625	4.12	3.08	2.85	2.69	2.49	2.36	2.18	2.08	2.02
	0.875	4.37	3.21	2.96	2.78	2.56	2.42	2.22	2.11	2.05
	1.25	4.53	3.29	3.02	2.84	2.6	2.45	2.24	2.13	2.07
	≥ 1.5	4.58	3.31	3.04	2.86	2.61	2.46	2.25	2.14	2.07

Page 78

Grade (%)	Length (mi)	Percentage of Heavy Vehicles
Grade (%)	Length (mi)	2	4	5	6	8	10	15	20	≥ 25
2.5	≤ 0.125	2.75	2.36	2.27	2.2	2.11	2.04	1.95	1.9	1.87
	0.375	4.01	3.02	2.8	2.65	2.46	2.33	2.16	2.06	2.01
	0.625	4.66	3.35	3.08	2.88	2.64	2.48	2.26	2.15	2.08
	0.875	4.99	3.52	3.21	3	2.73	2.56	2.32	2.19	2.12
	1.25	5.2	3.64	3.3	3.08	2.79	2.6	2.35	2.22	2.14
	≥ 1.5	5.26	3.67	3.33	3.1	2.8	2.62	2.36	2.23	2.15
3.5	≤ 0.125	2.93	2.45	2.34	2.26	2.16	2.09	1.98	1.92	1.89
	0.375	4.86	3.46	3.16	2.96	2.69	2.53	2.3	2.18	2.1
	0.625	5.88	3.99	3.59	3.32	2.98	2.76	2.46	2.31	2.22
	0.875	6.4	4.26	3.81	3.51	3.12	2.88	2.55	2.38	2.28
	1.25	6.74	4.43	3.96	3.63	3.21	2.96	2.6	2.42	2.32
	≥ 1.5	6.83	4.48	3.99	3.66	3.24	2.98	2.62	2.44	2.33
4.5	≤ 0.125	3.13	2.56	2.43	2.34	2.21	2.13	2.01	1.95	1.91
	0.375	5.88	3.99	3.59	3.32	2.98	2.76	2.46	2.31	2.22
	0.625	7.35	4.75	4.22	3.85	3.39	3.1	2.71	2.51	2.39
	0.875	8.11	5.15	4.54	4.13	3.6	3.27	2.83	2.61	2.47
	≥ 1.0	8.33	5.27	4.63	4.21	3.66	3.33	2.87	2.64	2.5
5.5	≤ 0.125	3.37	2.69	2.53	2.42	2.28	2.19	2.05	1.98	1.94
	0.375	7.09	4.62	4.11	3.76	3.31	3.04	2.66	2.47	2.36
	0.625	9.13	5.68	4.97	4.49	3.88	3.51	3	2.74	2.59
	0.875	10.21	6.24	5.43	4.88	4.18	3.76	3.18	2.89	2.71
	≥ 1.0	10.52	6.41	5.57	5	4.27	3.83	3.24	2.93	2.75
≥ 6	≤ 0.125	3.51	2.76	2.59	2.47	2.32	2.22	2.08	2	1.95
	0.375	7.78	4.98	4.4	4.01	3.51	3.2	2.78	2.56	2.44
	0.625	10.17	6.23	5.42	4.87	4.17	3.75	3.18	2.88	2.71
	0.875	11.43	6.88	5.95	5.32	4.53	4.04	3.39	3.06	2.86
	≥ 1.0	11.81	7.08	6.11	5.46	4.64	4.13	3.45	3.11	2.9

Page 79

Step 5: Estimate Speed and Density

Equation 12-1: Average speed estimation.

S = F F S - \frac{(F F S - \frac{c}{45}) {(v_{p} - 1, 400)}^{1.31}}{{(c - 1, 400)}^{1.31}} B P < v_{p} \leq c

(HCM7 Eq. 12-1)

Exhibit 12-6: Parameter values used in Equation 12-1.

Parameter	Definition and Units	Value/Calculation
FFS	Base segment FFS (mi/h)	Measured OR predicted using Equation 12-3
FFS_adj	Adjusted FFS (mi/h)	No adjustments
SAF	Speed adjustment factor (decimal)	1.00
c	Base segment capacity (pc/h/ln)	c = 1,900 + 20(F FS–45), c ≤ 2,300, 45 ≤ FFS ≤ 70
c_adj	Adjusted segment capacity (pc/h/ln)	No adjustments
CAF	Capacity adjustment factor (decimal)	1.00
D_c	Density at capacity (pc/mi/ln)	45
BP	Breakpoint (pc/h/ln)	1,400
a	Exponent calibration parameter (decimal)	1.31

Equation 12-11: Density estimation.

D = \frac{v_{p}}{S}

(HCM7 Eq. 12-11)

Step 6: Determine LOS

Exhibit 12-15: LOS criteria.

LOS	Density (pc/mi/ln)
A	≤ 11
B	> 11–18
C	> 18–26
D	> 26–35
E	> 35–45
F	> 45 or Demand exceeds capacity

6.2 Nomenclature

BFFS =	base FFS for the segment (mi/h).
BP =	Linear to curvilinear flow rate breakpoint value (1,400 pc/h/ln).
c =	capacity (pc/h/ln).
D =	density (pc/mi/ln).
D_c =	density at capacity (45 pc/mi/ln).
E_T =	passenger car equivalent of one heavy vehicle in the traffic stream (PCEs).
f_A =	adjustment for access point density, from Exhibit 12-24 (mi/h).
f_HV =	adjustment factor for presence of heavy vehicles (decimal).
f_LW =	adjustment for lane width (mi/h).
f_M =	adjustment for median type (mi/h).
f_TLC =	adjustment for total lateral clearance (mi/h).

Page 80

FFS =	free-flow speed of the segment (mi/h).
FFS_adj =	adjusted free-flow speed (mi/h).
LC_L =	left-side lateral clearance (ft).
LC_R =	right-side lateral clearance (ft).
N =	number of lanes in analysis direction (ln).
pc/h/ln =	passenger cars per hour per lane.
P_T =	proportion of SUTs and TTs in traffic stream (decimal).
PHF =	peak hour factor (decimal).
S =	space mean speed of the traffic stream (mi/h).
SAF =	free-flow speed adjustment factor.
TLC =	total lateral clearance (ft).
V =	demand volume under prevailing conditions (veh/h).
V₁₅ =	volume during the peak 15 min of the analysis hour (veh/15 min).
v_p =	15-min passenger car equivalent flow rate (pc/h/ln).