1. Multilane Highway Capacity Analysis
CE331 Transportation Engineering

2. Objectives Determine LOS for multilane highways
Determine number of lanes to ensure given LOS

3. Multilane Highways
Roadway facilities with some access control, usually in urban or suburban settings, with some flow interruptions, traffic signals at least 2.0 miles apart, with or without median, and lower design aspects than freeways

4. Multilane Highways (cont’d)
Factors affecting the flow on multilane highways
Uncontrolled access from roadside
Left turns (not explicitly considered in analysis)
Types of multilane highways
Rural or suburban
Divided or undivided

5. Multilane Highways

6. “Ideal” Conditions 12-foot lanes
12-foot total right and left shoulders
Divided highway
Only passenger cars
Level terrain
No intersections
Everyday commuters
FFS >= 60mph

7. Procedure for Determining LOS
Estimate free flow speed (FFS)
Calculate equivalent flow rate (vp)
Compute density (D=vp/S) and compare D to values in Exhibit 21-3 to determine LOS

8. Free Flow Speed FFS = BFFS - fLW - fLC - fM - fA Adjustment factors
fLW – lane width adj. factor, Exhibit 21-4
fLC – lateral clearance adj. factor, Exhibit 21-5
fM – median type adj. factor, Exhibit 21-6
fA – access point adj. factor, Exhibit 21-7
Base Free Flow Speed (BFFS)
No speed limit: 60 mph
Speed limit: +7 mph for SL 40 & 45 mph or mph for SL>=50 mph
85th Percentile speed: -1 for 40 mph to -3 for 60 mph

9. Lateral Clearance Adjustment
Divided
LC=Left+Right Shoulder
fM =0; fLC Exhibit 21-5 R L C L
Undivided
LC=6+Right Shoulder
fM = 1.6; fLC Exhibit 21-5 R

10. Equivalent Flow Rate (vp)
Adjust for vehicle mix and users
V: directional hourly volume (vph)
PHF: peak hour factor
N: number of lanes in one direction
fHV: heavy vehicle adj. factor
fp: driver population adj. factor, mostly =1

11. Heavy Vehicle Adj. Factor (fHV)
PT – truck and bus percentage
PR – recreational vehicle percentage
ET – passenger car equivalent for trucks and buses, Exhibits 23-8, 23-9, 23-11
ER – passenger car equivalent for recreational vehicles, Exhibit 23-8, 23-10

12. Example 1 FFS = BFFS - fLW - fLC - fM - fA 1.9 0.0 0.0 2.0 = 51.1 mph
4-Lane suburban divided highway; V=1,750 vph; 5% trucks; 11-foot lanes; adequate clearance both sides; 2% grade; 1.5 miles; 12 intersections; PHF 0.9; speed limit 50 mph; everyday commuters. LOS?
1.9
0.0
0.0
50+5=55
2.0
FFS = BFFS - fLW - fLC - fM - fA
= 51.1 mph

13. Example 1 (cont’d) V vp = PHF N fHV fp 1750 = 1045 pcphpl 1.00 0.90 2
0.05
2.5
0.0
fHV = 1/[1+PT(ET-1)+PR(ER-1)]
= 0.93

14. Example 1 (cont’d)
D = vp/S = 1045/51.1 = vpm

15. Example 2 4-Lane rural undivided highway; V=1,500 vph; 6% trucks;
12-foot lanes; 2-foot right shoulder; 1.5% grade; 1.5 miles; 10 intersections; PHF 0.88; speed limit 50;
everyday commuters. LOS?

16. Example 2 (cont’d)
D = vp/S = 877/50.8 = 17.3 vpm

17. Example 3
A 1.5 mile section of rural divided highway is to be designed to carry a directional volume of 2,500 vph and to operate at Level of Service C. The design speed and speed limit on the roadway will be 50 mph and it will be designed with no grade and only 3 cross intersections along the entire length. Data from similar roadways indicate that 6% trucks will be present and the PHF is expected to be If the available right-of-way is 90 feet, determine the cross section of the road to meet the design characteristics.