Module 2 : Traffic Measurement Procedures

Lecture 05 : Measurement at a Point

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

	Method based on relative delay The 1965 HCM used relative speed reduction to define PCUs for two lane highways and quantified this by the relative number of passing known as the Walker method. For multi-lane highways, PCUs were based on the relative delay due to trucks. PCUs for multi-lane highways based on relative delay may be found as $$E_t = \frac{D_{ij}-D_b}{D_b}$$ (1) where $D_{ij}$ is the delay to passenger cars due to vehicle type i under condition j and $D_b$ is the base delay to standard passenger cars due to slower passenger cars. PCUs in the 1965 HCM were reported for grades of specific length and percent, proportion of trucks, and LOS grouped as A through C or D and E. As expected, the highest PCU was reported for the longest and steepest grade with the highest proportion of trucks and the lowest LOS. However, in many cases the PCU for a given grade and LOS decreased with increasing proportion of trucks. PCUs in the 1965 HCM were reported for grades of specific length and percent, proportion of trucks, and LOS grouped as A through C or D and E. As expected, the highest PCU was reported for the longest and steepest grade with the highest proportion of trucks and the lowest LOS. However, in many cases the PCU for a given grade and LOS decreased with increasing proportion of trucks.