Question

1. A classification count of vehicles over a 40 day period follows:

Austroads Class	Vehicle Count
Class 1	25,500
Class 3	1,000
Class 4	2,000
Class 9	1,500

1. What is average daily traffic in terms of vehicles?                                      
2. What is the percentage of heavy vehicles?                                                
3. What is average HVAG/HV (NHVAG) using the typical heavy vehicle axle configurations for vehicle classes 3, 4 and 9?                                                                              
4. What are the heavy vehicle axle group proportions?                                  

2. A two-way 2 lane rural road (1 lane in each direction) has an estimated 1st year of design AADT of 15,000 vehicles. Given the following data, what is the design traffic loading in terms of ESA?     

Design period = 30 years; Annual growth rate = 3%; %HV = 15% NHAVG = 2.8 HVAG/HV; Average ESA/HVAG = 0.95

Answer 1

so we are given the vehicle count and so can calculate the total count over 40 days

So 30000 vehicles are counted over 40 days

So average daily traffic = 30000/40 = 750 vehicles/day

The Class suggests something about he type of the vehicle. I have listed it as follows

So assume that HEAVY VEHICLES = Class3, Class4 and Class 9 only we have

% of heavy vehicles = 4500/30000 = .15 = 15%

NHVAG = # of heavy axle vehicle groups per heavy vehicle including

SADT - Single Axle Dual Tire

TAST - Tandem Axle Single Tire

TADT - Tandem Axle Dual Tire

QADT - Quad Axle Dual Tire

For our data we have the following Heavy Vehicle Axle Group Proportions

NHVAG = average number of axle groups per heavy vehicle in a single day = (50 + 100 + 112.5)/(25+50+37.5) = 2.333

Typically FHWA classification for axles and vehicle classes shows as follows

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The Design Traffic Loading can be calculated using the formula

NDT = 365 * AADT * Directional Factor * Lane Distribution Factor * (%Heavy Vehicles in decimals) * GRN * NHVAG * ESA/HVAG

where

AADT = average daily traffic = 750

Directional Factor = take higher direction or .5 if 50-50

Lane Distibution Factor - in our case only one lane so this is 1

% heavy vehicles- we already calculated to be 15%

GRN = growh factor = [{(1 + Growth Rate) ^ Design life } - 1]/ Growth Rate

= (1.0330 - 1)/0.03 = 47.575

so NDT = 365 *750 * 1 * 1 * .15 * 47.575 * 2.8 * .95 = 5196439 ESAL's