City navigation 101: Black spots

This is the second part on my theories regarding city navigation. This one focuses on my theory on identifying black spots and working out how you can skip them.


There are two broad categories of bad traffic zones – really bad intersections, and convergence zones.

Really bad intersections
Some of these aren’t bad, so much as the intrinsic nature of the roads involved means that there is a high amount of traffic. Intersections of two (or more) major routes will result in this. Take the M5 and King Georges Rd (Met3). No matter what time of day it is, you will, more often than not, need to stop at this intersection. A really bad one is Epping Rd and Lane Cove Rd. Lane Cove Rd is frequently a carpark in peak hour.

Convergence Zones
I use this to refer to any formation wherein traffic is necessarily funneled into one area. This includes all types of crossings, bridges, and ‘entrances’. By entrance, consider the northern beaches. There are only 3 roads into the general region between Manly and Palm Beach – the Spit Bridge, Wakehurst Parkway, and Mona Vale Rd. Thus, anyone wanting to go to the Northern Beaches must go through one of these roads. Essentially, any road that is, practically or literally, the only way in, is in entrance. Crossings, in general, can refer to any crossing of a significant barrier to traffic. Geographical features, such as rivers and deep valleys, are the most obvious. But it also includes rail lines, motorways, and major roads with a median strip and a lot of no right turns.
Motorway entrances are special, in that they can be a horrible amalgam of both convergence zone and bad intersection. Think of the F3 entrance/Pearce’s Corner traffic zone, or the M4 entrance at Strathfield.

Navigating black spots
If to get from A to B I need to go through one of crossings C1, C2, or C3, then whatever happens, I need to work out which one of these easiest to get through, and whether the cost of taking the detour to C2 or C3 is worth the time saved going through C1. So let’s say you need to cross the harbour from the inner west. You can cross at the Harbour Bridge, Gladesville, or Meadowbank. If you’re going to Chatswood or thereabouts, both the Bridge and Gladesville are viable depending on time of day and where you’re actually starting from. But, really, there’s not much choice.
Crossing theory becomes much more useful when you realise that if you’re going straight through a bad intersection, you can treat it as a crossing. So, let’s go back to our old friend, Epping Rd and Lane Cove Rd.


Annotated Google maps image of Epping Rd and Lane Cove Rd intersection


The main intersection we can call our ‘C1′. Two other crossable intersections are marked in red. Knowing that C1 is a carpark in peak hour, I can instead try to work out whether these two – Herring Rd or Wicks Rd – is a workable alternative. Now, Wicks Rd is closer. But, to get on to it, it’s a right turn and the main intersection into this route is generally quite packed. Herring Rd, however, is one of those gems of a back road. This is because: A) the perceived distance (1km out, 1km back in) seems long, preventing people from thinking that this is a great back road. But at 50-60 kmh, this adds up to an additional travel time of 3 or so minutes off the unhindered straight through time. B) it’s a left turn that has several options in, should you realise too late that you’re heading into a carpark C) re-entering Lane Cove Rd at Waterloo is a “turn left at any time”, meaning that the cure is not worse than the disease. All up, a 20 minute stay in the carpark turns into a 5-10 minute bypass, depending on lights.

Now, for a different study: Parramatta Rd between the City Westlink and the M4 entrance.





This section of road is bad in a lot of different directions. Crossing Parramatta Rd is usually painful because the lights prefer the Parramatta Rd traffic. Going along it gets yourself stuck in the traffic leaving the city and wanting the M4 or vice versa. Thus the citizens of the inner west who have had to work their way around it have had to use on the many and various ways around.
Now, I could go at length about all the different ways I’ve used to go through, around, and behind Parramatta Rd. But there are too many different directions to work off. Instead, I will use this to illustrate a major idea about back road decision making.
There may be times when you’ve found a back road on the map, only to discover that some feature of the back road actually makes it take significantly longer. Most of these times, I’ve found, have been because of complicated navigation (which can be alleviated by practice), or because the way off onto the back road and/or the way back on to the main road are bad. Now, notice that Queens Rd becoming Gipps St runs parallel to Parramatta Rd. If one wanted to get to or past Concord Rd without the hassle of the M4 entrance/exit at Strathfield, this is certainly a viable option. However, it turns out that Gipps St into Concord Rd can be a spectacular fail in the weekend peak. This is because Concord Rd gets loaded on the weekend. Secondly, actually getting onto this road from Parramatta Rd is fraught with difficulty because of the large number of no-right-turns on Parramatta Rd. This means that the limited number of right turn points also get loaded. Typically, one needs to find another way in and out (there are some other back roads for both options).

So, to summarise:
1) most back road decisions can be reduced to working out how best to cross a particular obstacle. This involves finding other possible crossings.
2) The viability of these back roads is influenced by the ability to actually and easily get on to them and then to get back on to the main route.

Comments are closed.