Introducing Rodel Entry Capacity Calibration Arrival Turning Flows Traffic Flows Flow Modifiers Average Daily Traffic Time-sliced Profile Geometric Parameters Approach Geometry Entry Geometry Entry Width E Number of Entry Lanes ne Entry Radius R Entry Angle Phi (Ф) Circulating Geometry Exit Geometry Capacity Modifiers Calibration Bypass Geometry Bypass Approach Bypass Entry Bypass Exit Accidents Accident Models Accident Geometry Economics |
Geometry > Entry Geometry > Flare Length L' ## Flare Length L’Flare length is the distance from the entry to the halfway point in the approach. HCM does not use the flare length L'. When V > E then L' = 0. When E is greater than V, increasing L' will increase capacity. The increase in width from V to E should be at a uniform rate. The increase in capacity is proportional to the area (E-V) multiplied by L'/2. Consequently if E-V is very small, even a large L' will produce only a small increase in capacity. Even widening V to match the slightly larger E only increases capacity a little. When E is significantly greater than V, increasing L' produces large increases in capacity that level out at about 300 ft. With L' = ~312 ft (100 m) the capacity is 95% of the capacity achieved by widening V to match E.
If there is a parallel approach E wide for a distance d back from the yield line followed by a taper back to the approach width V then L' is measured from the back of the parallel section to the width (E+V)/2 as normal. However, L' is then increased by adding d. This is a good way of increasing capacity when a long L' from the yield cannot be achieved due to ROW constraints as d + a short L' can give the same capacity increase a longer L' with no parallel section. All the above depends on both E and V being effective. L' should also be effective with no parked cars etc. © Rodel Software Ltd |