General Road and Highway Discussion

[danbrotherston]

ijmorlan pid='74392' dateline='1572284748']

I'm not quite sure what you are suggesting for the separated right turn lane can you draw it out? Are you suggesting something like the right turn leg of this roundabout: https://www.google.ca/maps/@43.4268258,-...a=!3m1!1e3 (which I cannot comprehend the reason for anyway, there seems to be no justification for this lane). It sounds like it would take a lot of space...I'm still sure how it makes the crossing easier, it would still depend on the turn radii at the right turn.

A bit like that in shape, but more like the ones at University and Westmount or University and Weber in terms of size (sorry, I don’t have a convenient way of sketching something quickly right now, although really I should just put something together for that). Also I’m talking about non-roundabout intersections; I’m not entirely clear on why they add those to roundabouts. I think in principle it is supposed to reduce the amount of traffic using the actual circle itself but I have an idea that the right turn lane tends to jam up, leading people to use the circle, further increasing the incentive to avoid the right turn lane.

So as to shape, the one you pointed out starts by separating from the road, and it looks like maybe it will form an almost highway-like ramp to the other road; but then it curves back and meets the road with a curb radius like an ordinary intersection. My idea is to do that much on a much smaller scale. So if you imagine implementing the shape from the Google Maps aerial photo but on the size of one of the intersections I mentioned, that’s what I’m imagining.

As a pedestrian, I cross a single lane of traffic to get to the island. Right now, many people worry about the speed of cars making the right turn; but my idea is to have them slow as they reach the new street to turn a small-radius corner. Once I’m on the lane, I only have to cross the straight-through and left-turn lanes; and the corner can have a radius of 0 (well, OK, maybe 10cm because that is more reasonable to build out of concrete). If I’m crossing diagonally (both ways), I don’t interact with right-turning traffic at all while I’m changing from crossing one street to crossing the other.

Of course, there are still locations where having separate turn lanes doesn’t work at all due to space constraints, but I’m talking about a modification to the separated turn lane designs to make vehicle speeds more appropriate, so I’m only talking about locations where separated turn lanes already exist or are considered.

I hope that’s a bit more clear.

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

The bottom left is what it sounds like you are saying, a lane diverges from the road, and makes a gentle S towards the other road, where it makes a 90 degree turn. This would seem to take a considerable amount of space and resources, and would still leave pedestrians crossing high speed traffic at an oblique angle on one leg, otherwise, peds would have to walk very far out of their way to cross on the other leg (this is already the case for roundabouts).

There are a few other designs I thought were worth highlighting, the right has two sharp angles, it also requires a lot of space, but has low speed turns at both ends, this is probably only useful in places with a unique context which makes a right turn at the intersection impossible, otherwise drivers would ignore it, and make the easier turn at the intersection.  I wanted the region to use this on Victoria actually.

The upper left is a traditional regional death island, you'll note it matches exactly the wide and generous turn on actual Weber St.  The top right is something new the region is doing, where they change the geometry of the turn to make the decision point much later, in theory drivers are forced to slow down more and make it safer.

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.

As for the roundabout, I really have no idea, that turn ramp makes absolutely no sense to me at all, it isn't even the busiest leg of the roundabout....but that whole project leaves plenty to be desired anyway.