New designs were published for the Hwy 91 and Nordel interchange. And some were lamenting the old designs. However, the design honestly hasn't changed that much in terms of the "how" it works. The only real big difference is that the old design did not have a WB Nordel to SB Hwy 91 direction whereas the new one does. The unique thing about this design is that the light for NB Hwy 91 to WB Nordel retains the benefit of only stopping EB Nordel traffic and not also stopping SB Hwy 91 to EB Nordel traffic. (This light was in the old design). The new light in the design is for WB Nordel to SB Hwy 91 traffic and it interrupts that same EB Nordel traffic as the other light and also the EB Nordel to NB Hwy 91. The lights will almost certainly be timed with each other, acting as a "single" traffic light so to speak.
If you take away that WB Nordel to SB Hwy 91 in the new design, you basically end up with exactly the same functionality as the previous design.
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| New Design with two traffic lights |
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| Old design with one traffic light. |
Comments:
moosejaw: Could the NB Hwy 91 to Nordel WB be a parclo to eliminate a traffic light?
You could actually get rid of the first traffic light by allowing the onramp to Nordel Westbound to continue underneath Nordel into a parclo to the other side and it would make it free flowing leaving the remaing light to be the left turn lane going onto 91SB.
waves: Yes however, it would cause crossing conflict point on the highway which could be worse.
The problem with such a solution is that you would create a crossing conflict point on the Highway between those getting onto the bridge and those getting off before the bridge. If the truck volumes are high for either then its very possible that crossing conflict point could cause worse traffic congestion than the light they propose.
Illustration showing the crossing point conflict created by a parclo of NB Hwy 91 to WB Nordel.
c041v: That parclo would be an aggressive weave. There are also challenging utility restrictions and ground conditions.
The pier location of the existing structure and east abutment location of the new structure don't support this. It's an aggressive weave, and the parclo, as correctly surmised by another user is a substandard solution that does not work from a geometric perspective in that space. The Hwy 91 NB to Nordel Way EB movement is relatively low volume.
As for the complaints about the "additional" signals , the signal at Hwy 91C / 91 does halt the 91C EB through traffic to allow for Nordel Way WB to Hwy 91 SB, which is a very low (30 vph) movement, meaning the EB traffic will see a lot of green time in the cycle. It's a movement the contractor fought to eliminate, but was ultimately required by the Province to provide "all possible movements" at the interchange.
In response to, "No matter where road infrastructure gets built in BC, there is always an excuse about terrain", there's 8m+ peat layers for much of this project. Easy enough to solve from an engineering standpoint, less so from an economic perspective. Substantial ground improvements are required for most of the elements of the project, adding a few more bridges would have astronomically increased costs. BC is one of the most challenging jurisdictions to build any roads due to seismic design criteria and a dearth of flat land.
The Nordel interchange looks the way it does as most of the traffic volumes are on Nordel Way EB from Highway 91 and 17, not WB.
What nobody appreciates about the Highway 91C "choke point" location is that there are underground two FortisBC transmission lines, and an Overhead BC Hydro Transmission line that offered virtually no options outside of what is shown in this location due to utility envelope restrictions and settlement considerations.
If you think the price was high now, consider what it would have cost to alter the location of either of these utilities.
waves: Why wasn't a double trupet interchange considered?
They are so close to it with their current design. It would make the intersection free-flowing and with no conflict points. The only extra engineering different from the original new design would be a culvert for the EB Nordel on-ramp to the AF
SFPR#86. 2020-05-24.
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| Highway 91 and Nordel Interchange as a Double Trumpet |
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| Example Double Trumpet (yin yang interchange) in Myrtle Beach, South Carolina Source |
c041v: Lane numbers and widths of ramps may be a barrier to the design.
The left hand exits for Nordel EB to Hwy 91 NB and Nordel WB to Hwy 91 SB are a non-starter from a geometric perspective. Obviously a lot of other options open up elsewhere were this condition allowed.
Additional issues with this design:
The Highway 91 SB to Nordel Way EB ramp is currently two lanes, and needs to stay that way as it is a very high volume movement. The proposed Nordel Way Way to Hwy 91 SB laning is conveniently wedged between what is a very tight area. Interchange ramp lane widths vary between 3.7-4.8 m for tracking, which just won't fit in this space. You are also dropping a WB lane immediately after crossing the structure, which means you only have one Nordel Way WB through lane, which is less than the current design in terms of capacity. Sure, you could widen the existing structure to 5 lanes, but this comes with a huge cost increase as the existing structure is not being replaced with this design.
The Nordel Way EB to Hwy 91 NB ramp cuts under the existing embankment east of the current structure, necessitating an all new structure to accommodate this. Staging-wise, it would be very complicated to split or halve traffic on this abutment to build the structure, and schedule-wise (were you to build the bottom structure first) it won't work either.
The double trumpet could have worked if there was more space in this area, but there isn't - you need to work within the Right of Way limits shown on the drawings. Combined with the geometric preferences of the Province, not much else that could have been done here. Also, the green Nordel Way EB movement only has one intersection for traffic heading to AFB. All of the movements cited for full free flow interchange under a double trumpet design are relatively low-volume when compared to the high priority movements under the current design that are free flow. Essentially, high cost for little gain in performance.
waves: Can you clarify what exactly you mean by "geometric preferences of the Province"?
Also, just a note that the lines in the sketch were only intended to represent a geometric idea, rather than to show the specific lane configurations. I can see your concern with the limited of space in the south-west corner.
c041v: The level of comfort with innovative design solutions varies from jurisdiction to jurisdiction.
I simply meant that achieving the desired number of movements, lane & shoulder widths, curve radii and other considerations (such as no left hand exits) can act as significant constraints in developing a viable design.
The level of comfort with innovative design solutions varies a great deal across Municipal and Provincial jurisdictions, some are willing to try something progressive or unconventional to solve a problem, while others are incredibly rigid in their desires, no matter how short-sighted it may seem.
makr3trkr: Left hand exits exist around Metro Van. Should they really be a deal-breaker?
I would think any left hand exits in a potential double trumpet interchange to be more like a split Y junction than a true exit per se. The Queensborough bridge has two lanes exit right and one lane "continue" left for example. Not to mention numerous HOV left exits in the region plus I'm sure other examples ... I don't think it really should be considered a deal breaker. There's a similar wye/shared exit southbound on Knight to exit to 91 westbound to Richmond or to 91 eastbound to Delta.
Northbound on the Queensborough Bridge.
Northbound Highway 1 near Lougheed Mall
c041v: Fair points, but the rule book is pretty clear;
"DESIGN-BUILD AGREEMENT
Schedule 4: DESIGN AND CONSTRUCTION
Part 2: Design & Construction Requirement
ARTICLE 1 LANING AND GEOMETRICS DESIGN CRITERIA
1.2.3 Interchanges
(d) The use of left side exit and entrance ramps shall not be permitted."
Design-Build Agreement
The Queensborough wye dates back nearly 60 years, a lot has changed since then. The 91 SB exit off Knight street is not a true left hand exit, it is a two lane right hand exit that then wyes off after. Again, something from a different era.
Mininari: What if it was a right hand exit to Nordel Way?
Well there's an easy 'hack' to make it not a left-exit. Just sign / stripe the Eastbound-to-Northbound left turn movement as the PRIMARY movement, and make the split to Nordel Way the 'exit' -- it would thus be a right-hand exit, and not 'merge' with the 91 exit traffic if each of the 'exit-to-Nordel-Way-EB' traffic movements had its own dedicated lane up the hill.
waves: This is clever, however, how is the primary movement defined and what are the volumes?
I imagine that the primary movement is defined by the movement that has the highest volume and you can't simply pick it - If the numbers are close, or, are potentially inhibited by the current design (latent demand) then you may be able to make the argument that future expected movements should dictate the design. Does someone have the volume movements for the interchange and can share those numbers?
To speculate, just looking at the design proposed by the province for the green movement however, the through volume has two-intersections and the northbound on-ramp only has one. That might indicate to me that the primary movement is the northbound on-ramp. However, it is difficult to decipher intention from unintended consequence without the volume counts.
