2/27/06Michael Dixon1 CE 578 Highway Traffic Operations Lecture 16: Freeways Basic Sections

2/27/06Michael Dixon2 Objectives HCM 2000 procedure process Significant variables Adjustment factors

2/27/06Michael Dixon3 HCM Procedure Process Input data two parallel computations Two tracks to take for FFS Given the FFS and the adjusted volume

2/27/06Michael Dixon4 HCM Procedure Input Data Geometric data –Number of lanes –Grade –Lane width –Lateral clearance (right shoulder width) –Interchange density FFS –Base free-flow speed (BFFS) or measured FFS Volume –Drive population –Volume (vph) –Vehicle mix –PHF

2/27/06Michael Dixon5 HCM Free-Flow Speed Two tracks with field measured FFS or estimating FFS

2/27/06Michael Dixon6 HCM Field Measured Free-Flow Speed Track Measured at volumes up to 1300 pc/hr/ln Conducted at a location that is representative of the segment Speeds of all passenger cars or a systematic sample The average of the passenger car speeds is the field measured FFS

2/27/06Michael Dixon7 HCM Estimated Free-Flow Speed Track

2/27/06Michael Dixon8 HCM Estimated Free-Flow Speed Track (cont.)

2/27/06Michael Dixon9 HCM Estimated Free-Flow Speed Track (cont.)

2/27/06Michael Dixon10 HCM Estimated Free-Flow Speed Track (cont.)

2/27/06Michael Dixon11 HCM Estimated Free-Flow Speed Track (cont.)

2/27/06Michael Dixon12 HCM Volume Adjustment

2/27/06Michael Dixon13 HCM Volume Adjustment (cont.)

2/27/06Michael Dixon14 HCM Volume Adjustment (cont.) Hourly volume is adjusted up to a peak 15- minute volume by V/PHF PHF variations are larger for rural areas and off-peak periods

2/27/06Michael Dixon15 HCM Volume Adjustment (cont.) If the percentage of RVs is small relative to that of trucks Buses operate similarly to trucks Equivalents for extended freeway segments and specific grades

2/27/06Michael Dixon16 HCM Volume Adjustment for Grades Extended segment –No grade of 3% or more is longer than 0.25 miles or, –No grade of < 3% is longer than 0.50 miles Everything else should be analyzed as a specific grade

2/27/06Michael Dixon17 HCM Volume Adjustment for Grades (cont.): Extended Segments Level: Rolling: Mountainous

2/27/06Michael Dixon18 HCM Volume Adjustment for Grades (cont.): Extended Segments

2/27/06Michael Dixon19 HCM Volume Adjustment for Grades (cont.): Specific Grades Exhibit 23-9 Trends of E T are as follows: –Decreases with %heavy vehicles –Increases with length of grade –Increases with % grade Trends for E R are similar (see Exhibit 23-10) Trends for E T are similar for downgrades No adjustment needed for RVs on downgrades

2/27/06Michael Dixon20 HCM Defining Speed-Flow Curve Approaches that you can take: –Interpolate in the figure given in Exhibit 23-3 –Use equations below Exhibit 23-3

2/27/06Michael Dixon21 HCM Defining Speed-Flow Curve: Interpolation

2/27/06Michael Dixon22 HCM Defining Speed-Flow Curve: Equations

2/27/06Michael Dixon23 HCM Defining Speed-Flow Curve: Equations Note that the equation you use depends on which of the free-flow and adjusted volume conditions are satisfied. –If your FFS is 68 and your adjusted volume is 1200 pc/hr/ln which equation do you use? –If your FFS is 62 and your adjusted volume is 1700 pc/hr/ln which equation do you use?

2/27/06Michael Dixon24 HCM Calculate the Prevailing Speed Interpolating from Exhibit 23-3 Equations

2/27/06Michael Dixon25 HCM Calculate the Density q = u * k q = your adjusted volume (vp) u = your calculated speed Solve for k in units of pc/mi/ln

2/27/06Michael Dixon26 HCM Determine the LOS