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Terrain definition

Gustavo Riente de Andrade
TECTRAN - T├ęcnicos em Transportes ltda
Terrain definition was posted on August 2nd, 2011 at 3:59 PM EDT
regarding Chapter 4: Traffic Flow and Capacity Concepts

I was wondering which objective criteria do you use to classify the section general terrain as level or rolling, as the definition given by HCM is not totally conclusive and refers to the heavy vehicle performance.

Does that also implies that terrain classification could difer from region to region depending on the performance of the truck fleet?

Joseph Fazio
RE: Terrain definition was posted on January 9th, 2012 at 3:03 PM EST

Average truck population operational characteristics change through time and by location. For instance for average truck weight to horse power ratio between 125 and 150 lbs/hp:

                        Level       Rolling      Mountainous

1985 HCM Et 1.7 4.0 8.0 2011 HCM Et 1.5 2.5 4.5

In my opinion, if the designer or analyst have reason to believe that the truck population would be different from what normally occurs, use the specific grade Et. The 1985 HCM had separate PCU tables for trucks by 100 lb/hp, 200 lb/hp, and 300 lb/hp weight to horsepower ratios.

Gustavo Riente de Andrade
TECTRAN - T├ęcnicos em Transportes ltda
RE: Terrain definition was posted on March 15th, 2012 at 8:34 PM EDT

I agree. I our analysis, we've been prefering to segment the studied corridors in separate grades. Because this approach generates to many relatively short subsections, we usually agregate the individual results later with the use of the TT15 factor, presented in the two-lane highway chapter, unless a critical grade is found (LOS E or F).

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