ROUNDABOUT at In and OUT
3 min 15 second cycle!!! That's 195 seconds!! Horrible! 80 second delay is LOS F. How is 195?? Counting just the left turns and thru moves in during one signal cycle the following DEMAND vehicles must go through, All right turns can do a bypass lane. Left and Thru IN: about 250 vehicles in 3 minutes 15 seconds. This translates linearly to an hourly volume of: 4,615 vph. This is NOT including the right turns, which could be using a Bypass lane at each corner. The left turns (circulatory traffic) was 84 vehicles in 3.25 min, or about 1,550 vph. From FHWA https://www.fhwa.dot.gov/publications/research/safety/00067/000674.pdf on page 88 below, it shows a chart for a double lane roundabout. "The capacity forecast shown in the chart is valid for double-lane roundabouts with inscribed circle diameters of 40 m to 60 m (130 ft to 200 ft)." This calculates to a maximum flow entry of 1,320. This means the entry volume of the roundabout is 4 x 1,320, or about 5,280, so it looks like a 2 lane roundabout would work here, and that the V/C ratio would be 4,615/5,280 or about 0.87 or a high LOS D. Not the greatest. So we could have 3 lane entries instead and let Nees THRU traffic go thru easier, same with Blackstone traffic, give them 3 lanes too. This would probably result in LOS C or LOS B. |
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