Highway Engineering

The 16-hour flow is converted to an AADT value by applying the M-factor.

These valuations vary depending on the month in which the traffic count

was taken and by seasonality index. In the absence of robust long-term

and locally derived traffic data, default values of the M-factor for different

values of SI for each of the neutral months are calculated using the following

formula:

(4.26)

Values of the parameters a and b for all five neutral months together with

the M-factor values for differing values of seasonality index are given in Table

4.21.

Ma b=+ ¥()SI

100 Highway Engineering

Network classification E-factor

Motorway 1.15

Built-up trunk roads 1.15

Built-up principal roads 1.15

Non-built-up trunk roads 1.15

Non-built-up principal roads 1.15

Table 4.20Default E-

factor values (in the

absence of local

information) (DoT,

1996)

Parameter M-factor

Month a b SI =1.0 SI =1.25 SI =1.5

April 287 73 360 378 397

May 316 33 349 357 367

June 408 - 57 351 337 323

September 445 - 102 343 318 292

October 297 61 358 373 389

Table 4.21M-factor

scores for different

values of SI (DoT,

1996)

Table 4.22 shows the M-factor values for the five neutral months for the

five road classifications, given their typical SI values as indicated in Table

4.19.

M-factor

TBU/PBU MWY TNB/PNB

Month SI =1.0 SI =1.06 SI =1.10

April 360 364 367

May 349 351 352

June 351 348 345

September 343 337 333

October 358 362 364

Table 4.22M-factor

scores for motorways,

trunk roads (built-up

and non-built-up) and

principal roads (built-up

and non-built-up) for

the five neutral months