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How not to design a flyover

July 5, 2006

The problems with Bangalore's infrastructure are well-known. Everybody knows we have pathetic pot-holed roads, more traffic than the roads can handle, and an administration that talks through the wrong orifice about fixing things. Heck, we can boast that we are possibly the only city in the country, and perhaps the world, that has a traffic light on a flyover, thanks to the wonderful administration's short-sightedness.

But apart from the "oh my gawd, we didn't foresee the hordes of people moving in" excuse, there are certain problems with the way infrastructure, is  designed, that makes you wonder if we might indeed have better luck entrusting the planning work to a large group of chimpanzees, banging away at AutoCAD. For instance, at some places, you will find bus stops right after a traffic light. At others, you will find them around corners. This doesn't need some genius-level IQ to figure out, for cryin' out loud. Who in their right minds can't see that erecting a bus stop right after a damn traffic light is a sure way to cause a traffic block? Couldn't they move it, say, 200 metres ahead?

Another thing that the planners don't seem to understand is the concept of a "bottleneck". You simply have to look at Old Madras Road, where the 4 lane road is being widened to 8 lanes. Oh, that's a good thing, you think. Except that it's being widened only up to the point of a busy intersection, so all that happens is that the bottleneck shifts to another point instead.

Let me illustrate this in some detail with the example of the Airport Road-Koramangala flyover that's being constructed. This fine piece of work (I almost choked while writing that) was started in February 2003 and was supposed to be finished the same year, but of course, all kinds of bureaucratic problems (methinks somebody didn't get a big enough share of the "incidental expenses" pie) led to numerous delays and the first phase is apparently ready for opening in a fortnight - 3 years later.

The purpose of the flyover is to alleviate the congestion on Airport Road because the intersection of Koramangala Ring Road, Indiranagar 100 ft Road, and Airport Road is where three major streams of traffic meet. And anything that can ease traffic jams is good, right? Flyovers are supposed to help the smooth flow of vehicles without the problems of having a traffic light, aren't they? (Unless you're using the aforementioned Richmond Road flyover, of course.)

Well... not if you build them like the city of Bangalore does. When a layperson like me stands in front of the flyover construction site, it's glaringly obvious that all the flyover will do is to shift the bottleneck to another spot: the Indiranagar 100 ft Road.

Take a look at the diagram below. I have colour-coded the different streams. Vehicles coming from Koramangala are green, the ones coming from Domlur are red, and the ones going to Koramangala are purple.

 

Diagram 1

 

The Indiranagar 100 ft Road is a 3-lane road both ways (and barely one at that.) The flyover looks like it will have two lanes both ways. This wouldn't be so bad, except for the small problem that a bypass from the Domlur side of Airport Road (marked by "Domlur turn" also ends at pretty much the same spot. Airport Road is already a busy road, so traffic from there to the Indiranagar side via the bypass will not be insignificant.

The result: you have four streams of traffic leading into a road that's only capable of handling three.

Well, what do you expect when this kind of situation occurs? Some stream will get blocked. The diagram below shows exactly where traffic will rapidly get choked (shown in grey.)

Diagram 2

 

Hmmm, that's not good at all. Vehicles that are supposed to move fast over the flyover will slow down considerably, thanks to the choke at the end of it.

 

 

But wait, wait! There's more. Observant readers may have noticed that just 30 freakin' metres away from the termination of the flyover, there's a right turn. So you have vehicles coming from the Indiranagar side, wanting to turn right, and trying to negotiate their way into the right turn, not through speeding vehicles from the flyover, but through the traffic jam I described above. Take a look at the new scenario below. Vehicles turning right have been coloured blue.

Diagram 3

 

If this is what happens, and keeping in mind the legendary Bangalorean driver's consideration for other drivers (cough, cough), the jam will go from bad to worse (see the expanding grey.)

Ironic, isn't it, that a flyover designed to make traffic flow faster will do nothing of the sort? All because some dolts didn't realise that making four-lane traffic flow into three lanes creates a choke point.

 

Let's take a look at some of the possible options to work around this problem and figure out how viable they will be.

Option 1) Put a traffic light at the right turn so the blue vehicles can turn without running into an existing jam. Unfortunately, this is what will happen:

Diagram 4

Yes, if you make flyover traffic wait even 30 seconds for a green light, you'll have traffic piling up on the darn flyover itself. Oh, and on the Domlur bypass too. What fun, eh?

 

Option 2) Seal off the right turn so the congestion is eased. This may help a bit, but at peak time, say 6-7 PM, when traffic doubles or triples, you will see the heightened effect of four lanes flowing into three. Here's what you'll get:

Diagram 5

You now get two congestion zones instead of one. Worse, you risk the Domlur bypass pile-up to propagate on to the main airport road itself, and that just puts us back at square zero.

Lastly, after all this, I guess I should point out that the numerous traffic light stops and intersections on 100 ft. Road will make it difficult for fast streams of traffic to progress, with the result that the entire 2 Km stretch will be perpetually jammed like Cunningham Road currently is. That is the domino effect, amigos.

Suddenly those chimpanzees using AutoCAD seem like a better proposition, don't they?

 

I am no road planner, but as someone who's done a wee bit of programming in the past, I have some understanding of bottlenecks and scalability. The Koramangala-Indiranagar flyover looks like a disaster waiting to happen when it's thrown open to the public on July 15. It's a pity that spending millions of rupees wasn't enough to get someone half-sensible to design the darn thing well.

 

(I hope to start a small series soon on how traffic jams are caused in Bangalore. This will hopefully bring me out of my blog drought, caused by life giving me a hard time from all corners lately.)

Update: It seems the stupid politicans have already started damaging the flyover


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