Breezy Point, East New York: SimCity 4 tips and tricks (NAM36)

Discussion on Traffic Capacity – NWM Highway over Avenue Roundabout Two-Level Interchange

While the NWM Highway over Avenue Roundabout prefab interchange can be used as a simple two-level interchange highway stack, by using 1x2 AVE-4 stubs to do an inline transition to RHW-4, it suffers terribly from three major capacity issues:

1. The central AVE-4 roundabout has only 20% of the capacity of dual tile RHW-4, and 40% the capacity of single tile MIS.
2. The central AVE-4 roundabout handles 100% of non-turning traffic on two of the RHW-4 approaches.
3. The central AVE-4 roundabout handles 100% of left-turning traffic on all four of the RHW-4 approaches.  While right-turning traffic can be diverted using MIS slip roads, left-turning traffic is forced to go through the roundabout.

Furthermore, if you track capacity at the "corners" of the AVE-4 roundabout, the roundabout delivers a THREE TIMES traffic multiplying effect, with three "corners" of the AVE-4 roundabout being traversed by each left-turning path through the interchange.  Assuming 100% capacity on the RHW-4 approaches, and 33% right turning traffic, my calculations follow ...

On NAM High Traffic Simulator setting:

• 100% traffic capacity on all four RHW-4 approaches adds up to 60,000 vehicles per day.
• With 33% of that traffic turning left through the roundabout, that's 20,000 vehicles per day.
• Left-turning traffic has a THREE TIMES traffic multiplying effect through the roundabout, so that's 60,000 vehicles per day on the roundabout "corners".
• With 33% of two RHW-4 approaches proceeding straight through the roundabout, that's 10,000 vehicles per day.
• Straight traffic has a TWO TIMES traffic multiplying effect through the roundabout , so that's 20,000 vehicles per day on the roundabout "corners".
• In this 100% RHW-4 traffic capacity case, the AVE-4 roundabout "corners" would be faced with 80,000 vehicles per day, while the AVE-4 traffic capacity at 100% is merely 6,000, putting it at a crazy 1333% of capacity!  

That's assuming there are four MIS slip roads to bypass the roundabout for right-turning traffic.

Discussion on Traffic Capacity – This MHW x RHW-4 Three-Level Interchange

By comparison, the four central signalled OWR-2 x OWR-2 intersections are 50% higher capacity than the AVE-4.  Just as importantly, the straight traffic, assuming 33% of the RHW-4 approaches are proceeding directly through the interchange at L1 and L2, results in a 20,000 vehicles per day reduction of OWR-2 intersection traffic load.

The OWR-2 remains a weak point in the interchange, but for left-turning traffic only.  Here's my calculations on NAM High Traffic Simulator setting:

• With 33% of traffic turning left through the OWR-2 signalled intersections, that's 20,000 vehicles per day.
• Left-turning traffic has a THREE TIMES traffic multiplying effect through the OWR-2 signalled intersections, so that's 60,000 vehicles per day on the OWR-2 x OWR-2 intersections.
• In this same 100% RHW-4 traffic capacity case, the OWR-2 signalled intersections would be faced with 60,000 vehicles per day, while the OWR-2 traffic capacity at 100% is merely 9,000, putting it at 666% of capacity!

The OWR-2 is still a weak point in the interchange, but reasonable for moderate highway traffic cases.  In a 50% traffic case on all four RHW-4 approaches, with 33% left-turning traffic, the OWR-2 signalled intersections would be at 333% of capacity.