Introducing Rodel Entry Capacity Calibration Arrival Turning Flows Traffic Flows Flow Modifiers Average Daily Traffic Time-sliced Profile Geometric Parameters Approach Geometry Entry Geometry Circulating Geometry Circulating Width C Circulating Lanes nc Exit Geometry Capacity Modifiers Calibration Bypass Geometry Bypass Approach Bypass Entry Bypass Exit Accidents Accident Models Accident Geometry Economics |
Geometry > Circulating Geometry > Diameter D ## Diameter DThe diameter D is the outer diameter or Inscribed Circle Diameter. HCM does not use the D. The relationship between capacity and D is more complicated than other parameters. For a given circulating flow the increase in capacity, shown below, is moderate. However, increasing D gives greater increases in capacity the larger the circulating flow as shown below. Capacity is a small when opposing flows are large, so having a geometric parameter that increases capacity most when capacity is least is very useful. However, moderately increasing D increases the ROW disproportionately. On the contrary, moderately reducing the D can release enough land to widen entries and increase flare lengths sufficiently to achieve a large net gain in capacity. The effect of varying D should be checked with the accident models. © Rodel Software Ltd |