10-Traffic Characterization ( Highway Engineering Dr. Sherif El-Badawy )
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The document discusses traffic characterization and load analysis for pavement design. It describes the importance of accurately characterizing vehicle loads, configurations, traffic volumes and compositions. Key factors discussed include axle configurations, load equivalency factors (LEF) which convert loads to standard 18 kip equivalents, truck factors which summarize LEFs for each vehicle, and methods for estimating future traffic growth and directional/lane distributions. Accurately accounting for the full spectrum of traffic loads is important for designing pavements to last.
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10-Traffic Characterization ( Highway Engineering Dr. Sherif El-Badawy )
- 1. 1 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 1 Traffic Characterization Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 2 Traffic Loading • Primary input to any design procedure • Issues: • Vehicle Characteristics • Weight • Wheel and axle configuration • Frequency of occurrence • Traffic Volume • Current • Future (traffic growth) • Other • Lateral wander • Often not well-defined in practice Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Traffic Loads Characterization Pavement Thickness Design Are Developed To Account For The Entire Spectrum Of Traffic Loads Cars Pickups Buses Trucks Trailers Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Critical Response Values et ec et ec et at surface + bottom of all bound layers (cracking) ec at midthickness of all layers + top of subgrade (rutting)
- 2. 2 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 6 Traffic Composition Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 7 Axle Configuration Single Axle Single Tires Single Axle Dual Tires Tandem Axle Dual Tires Tridem Axle Dual Tires Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 8 Axle Configuration
- 3. 3 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Axle Configuration Parameters Axle Width Axle Spacing Tire Pressure Dual Tire Spacing Wheel Base Mansoura University - Faculty of Engineering – Public Works Engineering Dept. FHWA Vehicle Classes 1 2 3 4 5 6 7 8 9 10 11 12 13 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Normalized Truck Distribution by Truck Class El-Badawy, et al. TRB, 2012 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Sources of Traffic Data • Weigh-in-motion (WIM) • Automatic vehicle classification (AVC) • Traffic counts
- 4. 4 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Highway Graduation Project 2011 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 15 Design Approaches •Fixed Traffic •Fixed Vehicle •Variable Traffic and Vehicle Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 16 Fixed Traffic • Thickness design governed by single wheel load • Multiple wheels converted to equivalent single wheel load (ESWL) • Number of traffic repetitions is not a variable • Historical usage: • Airport pavements • Highway pavements w/ heavy wheel loads but light traffic volume • Method rarely used today Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 18 Important Definitions • Standard Axle Load (SAL): A single axle with dual tires that has a weight of 18,000 lb (80 KN). • ESAL: The number of repetitions of an 18,000 lb single axle load
- 5. 5 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 19 Equivalent Single Axle Load (ESAL) • Most common standard load • Developed at the AASHO Road Test • Load equivalency factors (LEFs) • The number of ESALs needed to cause the same damage as the load in question 1 ESAL = damage caused by one 18,000 lb single axle load Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Load Equivalency Factors (LEF) LEFs Can Be Based On: • Equivalent Stress or Strain at a Given Location (Mechanistic) • Equivalent Deflection at a Given Location (Mechanistic) • Equivalent Serviceability Loss (AASHTO) Mansoura University - Faculty of Engineering – Public Works Engineering Dept. LEF = EALF • Ratio of damage caused by a certain axle to that caused by the standard one. • Based on Fatigue, • LEF ≈ {Wi / Ws}4, where W = weight of axle • Based on AASHTO Equation: • For Flexible Pavements • For Rigid Pavements Mansoura University - Faculty of Engineering – Public Works Engineering Dept. AASHTO Load Equivalency Factors Load Equivalency Factor (LEF): No. of repetitions of 18-k SAL Load causing given PSI No. of repetitions of X- k Y-Axle Load for a same PSI Change for each: Pavement Type Thickness Terminal Serviceability.
- 6. 6 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. ESALF • Ratio of damage caused by a certain axle to that caused by the standard one. • Based on Fatigue, • ESALF ≈ {Wi / Ws}4, where W = weight of axle • Based on AASHTO Eqn, • For Flexible Pavements, see Equation in Next Slide Mansoura University - Faculty of Engineering – Public Works Engineering Dept. AASHTO 1993 Equation for LEF for Flexible Pavement Wtx = number of applications of given axle Wt18 = number of standard axle passes (18-kips single axle) Lx = load of axle group being evaluated, kips L2 = axle code (1 for single, 2 for tandem, and 3 for tridem, 4 for quad) b18 = value of bx when Lx = 18 and L2 = 1 pt = terminal serviceability index SN = structural number LEF = load equivalency factor tx t18 W W LEF 18 t x t 22x t18 tx β G β G )4.33log(L)L4.79log(L1)4.79log(18 W W log 1.54.2 p4.2 logG t t 3.23 2 5.19 3.23 2x x L1SN )L0.08(L 0.40β Where: ESALs 12,000 lbs LEF = 0.189 28,000 lbs LEF = 0.495 28,000 lbs LEF = 0.495 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. (Huang, 2004) Mansoura University - Faculty of Engineering – Public Works Engineering Dept. للطرق المصري للكود طبقا بها المسموح والحموالت المحاور أوزان
- 7. 7 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. للطرق المصري للكود طبقا بها المسموح والحموالت المحاور أوزان Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Approximate Relations to Compute LEF Mansoura University - Faculty of Engineering – Public Works Engineering Dept. REGULAR MIXED TRAFFIC Equivalent Number of 18k Single Axle Loads
- 8. 8 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 31 Truck Factor = S (Number of axles * LEF)/number of vehicles Truck Factor = S LEF = 0.189 + 0.495*2 = 1.368 ESALs 12,000 lbs LEF = 0.189 28,000 lbs LEF = 0.495 28,000 lbs LEF = 0.495 Truck Factors Truck Factor (TF) = sum of all LEFs for each truck Mansoura University - Faculty of Engineering – Public Works Engineering Dept. TF = 1.5 to 2.5 According to Egyptian Code 32 Truck Factor Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Truck Factors – Urban Vehicle Type Interstate Freeways Other Principal Minor Arterials Collectors Single-unit trucks 2-axle, 4-tire 0.002 0.015 0.002 0.006 - 2-axle, 6-tire 0.17 0.13 0.24 0.23 0.13 3-axle or more 0.61 0.74 1.02 0.76 0.72 All single units 0.05 0.06 0.09 0.04 0.16 Tractor semi- trailers 4-axle or less 0.98 0.48 0.71 0.46 0.40 5-axle 1.07 1.17 0.97 0.77 0.63 6-axle or more 1.05 1.19 0.90 0.64 - All multiple units 1.05 0.96 0.91 0.67 0.53 ALL TRUCKS 0.39 0.23 0.21 0.07 0.24 From MS-1, Table IV-5 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 34 Truck Factors – Rural Vehicle Type Interstate Other Principal Minor Arterials Major Collector Minor Collector Single-unit trucks 2-axle, 4-tire 0.003 0.003 0.003 0.017 0.003 2-axle, 6-tire 0.21 0.25 0.28 0.41 0.19 3-axle or more 0.61 0.86 1.06 1.25 0.45 All single units 0.06 0.08 0.08 0.12 0.03 Tractor semi-trailers 4-axle or less 0.62 0.92 0.62 0.37 0.91 5-axle 1.09 1.25 1.05 1.67 1.11 6-axle or more 1.23 1.54 1.04 2.21 1.35 All multiple units 1.04 1.21 0.97 1.52 1.08 ALL TRUCKS 0.52 0.38 0.21 0.30 0.12 From MS-1, Table IV-5
- 9. 9 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Truck Distribution - Rural Vehicle Type Interstate Other Principal Minor Arterials Major Collector Minor Collector Single-unit trucks 2-axle, 4-tire 43 60 71 73 80 2-axle, 6-tire 8 10 11 10 10 3-axle or more 2 3 4 4 2 All single units 53 73 86 87 92 Tractor semi-trailers 4-axle or less 5 3 3 2 2 5-axle 41 23 11 10 6 6-axle or more 1 1 <1 1 <1 All multiple units 47 27 14 13 8 ALL TRUCKS 100 100 100 100 100 From MS-1, Table IV-1 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 36 Truck Distribution – Urban Vehicle Type Interstate Other Principal Minor Arterials Major Collector Minor Collector Single-unit trucks 2-axle, 4-tire 52 68 67 84 86 2-axle, 6-tire 12 12 15 9 11 3-axle or more 2 4 3 2 <1 All single units 66 82 85 95 97 Tractor semi-trailers 4-axle or less 5 5 3 2 1 5-axle 28 13 12 3 2 6-axle or more 1 <1 <1 <1 <1 All multiple units 34 18 15 5 3 ALL TRUCKS 100 100 100 100 100 From MS-1, Table IV-1 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 38 Traffic Analysis ESAL = Equivalent 18,000 lb single axle load AADTi = First year annual average daily traffic for axle i in both directions Gjt = growth factor for growth rate j and design period t fd = lane distribution factor df = directional distribution factor Ni = Number of axles FEi = Load equivalency factor for axle i Ti = Truck Factor ESAL = 365(fd)(df)(Gjt)S(AADTi)(Ni)(FEi) using LEF ESAL = 365(fd)(df)(Gjt)S(AADTi)(Ti) using Truck Factor
- 10. 10 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Percentage of truck traffic traveling in one direction 47% 53% Directional Distribution Mansoura University - Faculty of Engineering – Public Works Engineering Dept. ADT 20,000 25% trucks 75% trucks ADT 60,000 8% trucks 39% trucks 53% trucks Design for worst case!! Lane Distribution Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Lane Distribution Factor N o. of Traffic Lanes in each Direction % Trucks in Design Lane 1 100 2 80–100 3 60–80 4 or more 50–75 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 42 Direction and Lane Factors (dfXfd) Number of Traffic Lanes (Two Directions) % Trucks in design lane 2 50 4 45 6 or more 40
- 11. 11 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. 43 Growth Factor (G) (Huang, 1993) Based on standard compound growth equations. r r G n 11 r = growth rate n = Design period, years For annual growth rate (r=0), G = n r = 2 -7 % Egyptian Code Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Example of Single Axle Growth 0 100000 200000 300000 400000 2000 2010 2020 2030 2040 Year Projectednumberof singleaxles Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Example 1 - Calculation of ESALS Axle Load, kips # of Axles per 1000 trucks Single Axles 2 753 4 299 6 105 8 34 10 42 12 30 14 41 16 93 18 110 20 80 22 50 24 11 Axle Load, kips # of Axles per 1000 trucks Tandem Axles 14 1 16 5 18 15 20 20 22 36 24 42 26 84 28 92 30 50 32 12 34 8 36 4 38 2 40 1 42 1 Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
- 12. 12 Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Axle Load Spectra 0% 2% 4% 6% 8% 10% 12% 14% 16% 18% 0 10000 20000 30000 40000 50000 60000 70000 80000 90000 PercentAxles Axle Load, lb 000169-South,VC 9, Tandem Axles January February March April May June July August September October November December El-Badawy, et al. TRB, 2012