Casey Overpass

clayville said:
I thought that closing image for the presentation on Wednesday was really misleading and unfortunate. In February this year, DCR held two large meetings and smaller charettes with stakeholders and the Toole Design Group concerning a plan to improve access and facilities on the Arborway between Jamaica Pond and Forest Hills. I wrote up the following about the presentation of their Starter Idea after those meetings:
Arborway Facilities

The traffic engineers who floated that spaghetti bowl above this week were not part of the February meetings and are not, I don't believe, part of next week's meeting either. Because of all that, I don't think this image should be considered either a preview of next week or an outcome of the work that has already been done.
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From the project map it looks like both Beta Group AND Toole are on-tap to provide a Murray Circle design?

The Toole sketch in your blog post certainly looks much more bike-friendly, and given what we've all seen at Alewife less likely to lock up with car traffic. I guess we get to see Toole's more developed version next week.
 
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Wow, that image above looks like it was created by someone who sells traffic signals! I seems truly bizarre that anyone would propose a six-way signalized intersection in this day and age.

The Toole Design Group sketch of a double roundabout configuration for this intersection seems much more reasonable; fewer conflict points, no light to cause backups, lots of pedestrian crossings, and off-street bike paths:
Murray.jpg

(Image snagged from Clayville's web site)

Toole is the same company that did the new Cambridge Bicycle Plan, Boston Complete Streets manual, Portsmouth's Bicycle Master Plan, and the forthcoming MassDOT bicycle design guidelines. They really get "complete streets" and multimodal design for all users.
 
The DCR meeting last Wednesday also proposed (as one option) a two lane rotary to help make the Walter/Centre Street intersection safer. Of course, the designers described is as a roundabout... I will give them a bit of leeway here; it is smaller than an official MDC rotary; after all we are talking about the DfCR (All credit to Bikeyface for that one: Department of fast Car Recreation)
Beta was, at least, better prepared at this meeting to actually discuss turning volumes and lane widths. It would have been very helpful if they had shown cross sections with property lines and current R.O.W. to help evaluate the proposed/suggested improvements. Also, A diagram of pedestrian desire lines, especially for the Emerald Necklace would have been most useful. The presentation can be found here: www.mass.gov/eea/docs/dcr/news/public-meetings/materials/projects/dcr-centrestreet-20151007.pdf
I am looking forward to Toole's presentation next week.
 
elemenoh said:
Wow, that image above looks like it was created by someone who sells traffic signals! I seems truly bizarre that anyone would propose a six-way signalized intersection in this day and age.

The Toole Design Group sketch of a double roundabout configuration for this intersection seems much more reasonable; fewer conflict points, no light to cause backups, lots of pedestrian crossings, and off-street bike paths:
Murray.jpg

(Image snagged from Clayville's web site)

Toole is the same company that did the new Cambridge Bicycle Plan, Boston Complete Streets manual, Portsmouth's Bicycle Master Plan, and the forthcoming MassDOT bicycle design guidelines. They really get "complete streets" and multimodal design for all users.
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I have driven some new double and even triple roundabouts in Wisconsin recently. They do seem to work for both traffic flow and traffic calming. But I would be very concerned about navigation confusion -- particularly the poor way we do signage around here.
 
Seeing the word 'roundabout' more and more. We are going to lose the word 'rotary' aren't we?
 
Really? I did not know that. How so?

Edit: Hmm, according to this, a lot of what we in New England call (and are labeled -i.e. West Roxbury Parkway ) 'rotaries' are technically now considered to be 'roundabouts'.

So, in a way, my point still stands. The local, traditional labeling is being eroded in favor of the modern, 'official' terminology.

Such is life.
 
An actual traffic engineer would have a better explanation than I can provide, but the Arborway rotaries (Murray Circle at Centre St, the doomed Shea Circle at Morton St) were designed solely to ease motor vehicle passage in the 1930s rather than provide any sort of "traffic calming" - they're large diameter free-for-alls designed when traffic volumes were much lower (and long after Olmsted). The article you found, and almost every one I've found, uses the phrase "modern roundabout" to indicate a multi-modal intent and typically describes and recommends much smaller diameters for safety, with other design features that make for safer use by pedestrians and bikes.

Here's some even more exhaustive detail about the varieties of Dutch roundabouts:
Looooong article about roundabouts
 
Right, the roundabouts I was referring to in Wisconsin are the tight diameter types, with very specific lanes and directed traffic flows. Nothing like our old free-for-all rotaries.
 
Some of the most interesting notions in Toole's February presentation on roundabouts - to me at least, who had never thought about them in depth - concerned the various elements that contribute to traffic calming and safety. Reduced sightlines for cars causes them to slow down. Tighter radiuses and negative cambers (roadway slopes that lean away from the center rather than into it) discomfort drivers at speed and slow them down. Lanes that deflect vehicles within and exiting the roundabouts increase safety for all.

It will be interesting to see in next week's presentation of the evolved plans just how far DCR is willing to go towards their admirable ideal that "A parkway is not a road. It is a park with a road in it" (from their Historic Parkways of Massachusetts Initiative). Somehow I reckon the raised crosswalks initially proposed throughout will get more than a little blowback if they're still in the plan... Murray Circle is shaping up to be an epic Cars vs. Everything Else battle imho, with current traffic issues frustrating to all.
 
Well, as a resident traffic engineer, I can say that rotaries (extremely large diameter ones) are being phased out and roundabouts are working their way back in to our design toolboxes. And the CAD programs that are available to us for design purposes make the layouts so much easier these days.

But the one major issue that can screw up even the most well designed roundabout is when one of the departure streets backs up into the circle due to downstream queuing. Once a roundabout gets backed up, everything goes to hell in a hurry. That's the one case where a signalized intersection, particularly a coordinated one, can effectively mete traffic so as to avoid a jam at peak periods.
 
Yeah, that's why it's best to keep roundabouts away from traffic signals. One keeps the flow going, one keeps stopping it.
 
North Shore said:
But the one major issue that can screw up even the most well designed roundabout is when one of the departure streets backs up into the circle due to downstream queuing. Once a roundabout gets backed up, everything goes to hell in a hurry. That's the one case where a signalized intersection, particularly a coordinated one, can effectively mete traffic so as to avoid a jam at peak periods.
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We can attest to that in Worcester. Washington Square ALWAYS backs up due to the light at Foster St, as well as the on-ramp to 290 westbound.
 
Meh. The gridlock makes it easier for peds leaving Union Station.
 
I really like the idea of this double roundabout. It's so...different. I also think that reversing the travel directions of the carriage ways is a great way to discourage the cut through traffic on them. This is going to be one of those plans that the public will just have to '"trust" the designer on. I bet everyone who shows up to the meetings will just say "no way" just because it's so new to them.

It looks like the conceptual striping though doesn't allow the City portion of Centre St proper access though. I think they need some dashed lines.
 
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