Traffic loading and VolumeTraffic loading and Volume

Prof. Dr. Prof. Dr. PadmaPadma BahadurBahadur ShahiShahi

1

2. Equivalent Axle load factor2. Equivalent Axle load factor

An equivalent axle load factor ( EALF) defines the damage per pass to a pavement by the axle in question relative to the damage per pass of a standard axle load; usually the 18 kip (80 kN) single axle load. (80 kN) single axle load.

The design is based on the total number of passes of the standard axle load during the design period, defined as the equivalent single axle load (ESAL) .

2

Calculation of ESALCalculation of ESAL

m = the number of axle load groups, m = the number of axle load groups,

Fi= the EALF for the ith axle load group,

ni= the number of passes of the ith axle group

during the design period.

3

Traffic AnalysisTraffic Analysis

To design a heavy pavement, it is necessary to predict the number of repetitions of each axle load group during the design period. Information on initial traffic can be obtained from field measurements. from field measurements.

The initial daily traffic is in two directions over all traffic lanes and must be multiplied by the directional and lane distribution factors to obtain the initial traffic on the design lane.

4

Future Traffic estimationFuture Traffic estimation

A -is the number of vehicles per day for design;

P - Is the number of vehicles per day at the last

nrPA )1( +=

P - Is the number of vehicles per day at the last

census;

r Annual rate of increase in traffic and may be

taken as 0.05;

n Number of years between last census and

years of consideration for widening.

Traffic Engineering 5

Vehicle damage FactorsVehicle damage Factors

Lane distribution factorLane distribution factor Single lane roads: Traffic tends to be more channelized on single

roads than two lane roads and to allow for this concentration of

wheel load repetitions, the design should be based on total number

of commercial vehicles in both directions.

Two-lane single carriageway roads: The design should be based on

75 % of the commercial vehicles in both directions.

Four-lane single carriageway roads: The design should be based on Four-lane single carriageway roads: The design should be based on

40 % of the total number of commercial vehicles in both directions.

Dual carriageway roads: For the design of dual two-lane

carriageway roads should be based on 75 % of the number of

commercial vehicles in each direction. For dual three-lane

carriageway and dual four-lane carriageway the distribution factor

will be 60 % and 45 % respectively.

Calculate cumulative standard axle Calculate cumulative standard axle Two lane carriage way

Initial traffic in the year of completion of construction = 400 CVPD

(sum of both directions)

Growth rate: 5%

Design life = 10 years

Vehicle damage factor based on axle load survey = 2.5 standard axle

per commercial vehicleper commercial vehicle

Period of construction 2 years