R300 North Phase 1, Cape Town

[jackal]

In another thread Peter asks:

Are there still plans to complete the stack and extend R300 northwards from there?

There are indeed, with a consultation between 14 November and 14 December 2023.

The plan is to extend the R300 as a mostly six-lane freeway up to the "urban edge" north of Durbanville. Here's a general overview:

The N1 stack (in green) will be completed. The next junction along (De Bron) will be a half diamond, north-facing only. There's eight lanes from there to Legato, a diamond. The northernmost junction, Wellington, is also a diamond.

SANRAL are responsible for the green section, the Western Cape government for the blue section. The urban edge is an arbitrary administrative line, so the road would not really stop there, one hopes. The detailed plans do show the route continuing beyond there - presumably to the N7 as part of a future phase.

They plan to lower the N1 at the stack, presumably so the R300 can be inserted as a second level, between the N1 and the ramps (note the R300 runs left to right):

I guess the original plan was to run the R300 over the top as the fourth level?

The consultation docs are at gnec.co.za - go to Documents on Review then 20683_SDBAR_R300.

The main doc seems to be the second draft BAR, near the bottom of the list. High quality layouts are available through Addendum B_Site Plans

[Peter Freeman]

Thanks Jackal. Those plans look good.

I've since found more info, including about the further extensions at each end to ultimately form a large Cape Town 'ring road'. Looking on G.Maps and G.Earth, and at my ancient paper maps of CT, it's easy to trace (through grassy reserves) the route for the south-western extension to meet up with M38 at Parkwood.

The impressive plan is, I think, far in the future, considering that the existing part was there for forty years before the current extension's awakening.

(Your https://gnecza-my.sharepoint.com links don't work for me)

[jackal]

Thanks Jackal. Those plans look good.

I've since found more info, including about the further extensions at each end to ultimately form a large Cape Town 'ring road'. Looking on G.Maps and G.Earth, and at my ancient paper maps of CT, it's easy to trace (through grassy reserves) the route for the south-western extension to meet up with M38 at Parkwood.

The impressive plan is, I think, far in the future, considering that the existing part was there for forty years before the current extension's awakening.

(Your https://gnecza-my.sharepoint.com links don't work for me)

Thanks Peter. In the OP I've now given a more fiddly but hopefully functional way to reach the docs. It will still likely require some reloading.

Addendum B includes a rejected alternative with C/D lanes (yes, proper ones, with their own grade separation):

I thought even the proposed D3M was extravagant, given how sparsely populated the area north of an extended R300 would be. But apparently there's a proposal for a city of 800,000 people, called Milkwood City, north of where the R300 would meet the N7. That'd do it.

[Peter Freeman]

They plan to lower the N1 at the stack, presumably so the R300 can be inserted as a second level, between the N1 and the ramps ... I guess the original plan was to run the R300 over the top as the fourth level?

I'm sure it would have been, as that would have resulted overall in the lowest gradients for turning movements. I suppose lowering the N1 avoids some aesthetic downsides for nearby homes, by limiting the total height. Also, I suppose it requires only earthworks (excavation) and a smaller bridge, rather than a long N-S aerial viaduct.

An afterthought: wouldn't it be cheaper to leave N1 alone but build the R300 as the lowest level, with the same degree of gradient disadvantage? Still one bridge to build, and the same excavation effort, but less disruption.

[Peter Freeman]

Addendum B includes a rejected alternative with C/D lanes (yes, proper ones, with their own grade separation):
R300 alternative - Copy.JPG

For the usual valid reason I suppose - De Bron, Legato and Williams are all fairly close together. But rejected anyway, of which I approve: too extravagant!

My view (which I've expressed previously, and I know is not shared) about C/D lanes for weaving mitigation is that they're often not the best (ie. most cost-effective) solution. They introduce unnecessary build complexity, navigation confusion, signage clutter, and they waste space. I believe equal mitigation can be achieved simply by generous lane provision: instead of 2-3-3-2, build D5.

The alternative, where exit volumes are high enough, is an auxilliary lane between junctions - every junction is a lane-drop/lane-gain. The northern stretch of Melbourne's M80 is like this. Also, as you stated, R300 will use this alternative: D4 between De Bron and Legato.

Surprisingly, in Melbourne we have few C/Ds, even though a casual glance reveals several areas of >2 carriageways. Most of these are actually early-diverging or late-merging simple ramps, for reasons of fit or for braiding. Even braiding is not frequent.

Melbourne's only long (7km) stretch of genuine C/D has just been commissioned on the now-Q3 Westgate Freeway: between its M80 interchange and the Westgate Bridge it has D3 inner express lanes. When you take shoulders and hard-strips into account, this whole length at similar (or lower) cost could have been D7. I'm certain that there will be confused drivers ending up on the bridge when they really wanted the tunnel.

To get to the bottom of this arrangement, tolling, not just weaving, must be taken into account. The tunnel will be tolled, but the widened Westgate Freeway will remain free, since it always has been. However, for trucks only, the outer carriageways only WILL be tolled. The C/D arrangement facilitates this distinction. The whole project was initiated by Transurban, of course ...

A shorter stretch of genuine C/D is at the fork of M2 and M79. Outbound, a C/D diverges left to deal with the Bulla Road and English Road interchanges. It re-joins M79 after 1.5km, and M2 after 2.5km. Inbound, C/Ds diverge from M2 and M79 to deal with Bulla Road and Bell Street, rejoining M2 5km downstream.

I thought even the proposed D3M was extravagant, given how sparsely populated the area north of an extended R300 would be. But apparently there's a proposal for a city of 800,000 people, called Milkwood City, north of where the R300 would meet the N7. That'd do it.

Fascinating. I just read-up on Milkwood. However, I won't hold my breath to see that.

[jackal]

An afterthought: wouldn't it be cheaper to leave N1 alone but build the R300 as the lowest level, with the same degree of gradient disadvantage? Still one bridge to build, and the same excavation effort, but less disruption.

The report says the foundations for the existing ramps are in the way of a lowered R300.

Curiously they don't even mention the top level flyover as an alternative. I agree visual intrusion will be a major consideration given there's housing on all sides.

[booshank]

Wow I never thought I'd see this seriously considered for completion! I remember my parents had a Cape Town A-Z from the early 1980s, from memory the R300 south of the N2 was labelled "under construction" and north of the N2 "planned". South of the N2 was labelled "Cape Flats Motorway", the use of "motorway" in SA seemed slightly strange and old-fashioned. Also remember the Swartklip interchange under construction sometimes late 1980s/early 1990s.

Are we sure that the present semi-directional T is actually the incomplete four level stack that was originally planned or is it possible that it was modified when the part north of the N1 was abandoned? That could explain the need for the proposed modifications.

Sadly I think that A-Z is long gone as from memory it had other slightly fantastical dashed in "proposed" schemes like a southern extension of the M3 above Boyes Drive on the side of the mountain above Muizenberg and St James.

[Peter Freeman]

Wow I never thought I'd see this seriously considered for completion! I remember my parents had a Cape Town A-Z from the early 1980s, from memory the R300 south of the N2 was labelled "under construction" and north of the N2 "planned". South of the N2 was labelled "Cape Flats Motorway", the use of "motorway" in SA seemed slightly strange and old-fashioned. Also remember the Swartklip interchange under construction sometimes late 1980s/early 1990s.

I still have a few 1970's Capetown maps. Two of my detailed street maps were published by Mobil. They don't show any of R300 (my 'Dead Rat Parkway'), but it was drawn in by me (Crayon Time!), and labelled 'Cape Flats Freeway'. I didn't draw it southwards as far as the N2, but I drew in several other planned roads that I learnt of. I left SA in 1977.

Are we sure that the present semi-directional T is actually the incomplete four level stack that was originally planned or is it possible that it was modified when the part north of the N1 was abandoned? That could explain the need for the proposed modifications.

It could. Morals of the story: never say 'never', and don't shoot yourself in the foot.

Sadly I think that A-Z is long gone as from memory it had other slightly fantastical dashed in "proposed" schemes like a southern extension of the M3 above Boyes Drive on the side of the mountain above Muizenberg and St James.

My Mobil maps show some freeways under-construction 1974-ish, eg. the M3 southwards as far as Steenberg (which is where it still ends). They show it as planned to continue southwards as you describe, and to then sweep clean across the peninsula just north of FishHook - possibly as sub-motorway from there. That's the line of present-day M65, Kommetjie Road, whose eastern terminus was visibly built for it.

As I mentioned upthread, Cape Flats Freeway south of N2 would have continued westwards to abut present-day M38's eastern terminus, thus completing the connection to M3 and thence down the peninsula.

[jackal]

Are we sure that the present semi-directional T is actually the incomplete four level stack that was originally planned or is it possible that it was modified when the part north of the N1 was abandoned? That could explain the need for the proposed modifications.

It could. Morals of the story: never say 'never', and don't shoot yourself in the foot.

The N1eb to R300 ramp looks to be at the third level for much longer than is necessary to clear the R300 to N1eb ramp below it. GSV looking up from the N1 gives the distinct impression of a bridge over nothing. I surmise that this is future proofing so a new R300 to N1wb ramp can be inserted underneath.

Further, the drawing in the OP seems to show this new "ramp G" in this position, below the existing ramp C. This would be impossible if the interchange had been built purely as a semi-directional T.

Though the interchange looks likely to be completed to a different configuration than that originally intended - ramps on the top like Texan stacks rather than in the middle like Merstham - most of the future proofing will still be utilised, showing its value and flexibility.

[booshank]

My Mobil maps show some freeways under-construction 1974-ish, eg. the M3 southwards as far as Steenberg (which is where it still ends). They show it as planned to continue southwards as you describe, and to then sweep clean across the peninsula just north of FishHook - possibly as sub-motorway from there. That's the line of present-day M65, Kommetjie Road, whose eastern terminus was visibly built for it.

As I mentioned upthread, Cape Flats Freeway south of N2 would have continued westwards to abut present-day M38's eastern terminus, thus completing the connection to M3 and thence down the peninsula.

Interesting, it's still obvious where the R300 would continue to the west there, but I'm sure there was nothing marked there on the early 80s map so it seems to have been abandoned early. I've never seen a map of how that part might have looked, which is odd as I'd have thought it would be reasonably straightforward to build and pretty useful (the opposite of the M3 southern extension which would have been an engineering challenge and useful to rather few people). That signalised T junction at the Vanguard Drive end looks very temporary too.