General Road and Highway Discussion

[danbrotherston]

I have mocked out a few different options (I just used preview on mac) to try and guess what you are saying.

[....]

But all of these lead to a really big point, what problem exactly are we trying to solve here? Why are we creating turns different from simple tight narrow turns?  The original reason for the ped island and slip ramps was to increase vehicle speeds in turns, I see this as an anti-goal, I don't really understand why we wouldn't just aim to go back to a traditional tighter corner with lower speeds all throughout.

I just took a look on Google Maps. The 3 that exist at Westmount and University are pretty much I’m looking for, except I would probably try to go for a smaller radius where each lane ends and less forgiving curbs (keeping in mind that large trucks do still need to be able to make the turns).

https://goo.gl/maps/DrSjQDPGTX6PXG15A

The problem we are solving is making it better for everybody, especially pedestrians. I would much rather cross Westmount and University, even with the fairly broad radii currently in place, than a comparable intersection without separated turn lanes. Crossing a single lane of one-way traffic is almost always easy, even if it is moving fairly quickly. Then, with that out of the way, the radius at the main intersection is effectively zero, minimizing the crossing distance. And if I’m crossing both ways, I don’t interact with the right-turning traffic at all when I’m ending one crossing and beginning the other.

I don’t like the islands at Weber and University; they are too small, and the lanes are just smooth curves. Also traffic isn’t forced to choose where it’s going until rather close to the intersection so the ease of crossing what I called a single lane above is reduced — really I need to watch other lanes for people pulling late maneuvers. By contrast at Westmount the islands have lots of space and traffic pretty much has to choose where it’s going some distance back from the crossing.

Some numbers crossing Weber at University:

North side (islands): 18.1m
South side (no islands): 23.7m

I don’t like the existing islands there, but rebuild that intersection with the same islands as at Westmount and University and I’ll take them any day.

Of course another approach, which is, um, a little hard to retrofit into existing roads but would actually be perfectly practical if adopted as a design approach for an entire new area of a city, would be to put the sidewalks about 100m away from the roads. Then put a pedestrian refuge and pedestrian crossings where the sidewalk crosses the roads. No turning traffic or other complexities and only need to cross 2 lanes at a time no matter how many turn lanes there are at the intersection. Put parking lots immediately next to the road, and buildings either on both sides of the sidewalk or only on the non-road side, depending on how much parking is needed.

I see.  So what you are describing are what the region refers to as something like "enhanced, delayed decision point slip lane" (because drivers must slow down and nearly stop at the corner instead of being able to turn at speed) and they are preferred by regional engineers in new construction.

Yes, they are not as bad as traditional turn islands. But I disagree that these are better for peds than no slip lanes, yes, they do reduce the crossing distance, but I still don't believe drivers are looking for peds while making turns, the main goal is still to benefit drivers, why not just have a tighter turn with no slip lane.  The value here is only that drivers can turn faster.  Large trucks can easily make these turns, even far tighter turns. They're only "better" when prioritizing cars is the assumed condition.