Hosur Road : 4 lanes better than 6
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Written By srkulhalli - 29 August, 2009
Traffic
Bangalore
Hosur Road
Road Works
lanes
suggestion
Road design
Transportation
Infrastructure
[Admin's note: These are the sort of posts that need to be highlighted on Praja - Aggregated or Original analytical work to talk specifics about the problems or solutions.]
This is a sister blog to my previous blog
http://praja.in/en/blog/srkulhalli/2009/08/05/redesign-hosur-road-model-road-footpath-and-cycle-tracks
This blog deals only with the vehicle part (as against footpath/cycle track which please comment solely on the other blog)
Current plan is to have 6 lanes, including median this is around 22m. I am cut pasting IDS comment here -
"This way you get a well engineered 4 lane road with ample ped+cycle infrastructure with trees parking and all. WIth 6 lanes you dont get turn lane, parking, trees and end up with squeezed ped path. If 30 meters not available cut down the parking in those streches, you will get 3+ meters. If still running short cut center lane you will get another 3+ meters. You will still get uninterrupted 4 lanes+ped+cycle.
If turn lanes are required only at the junctions that space during the rest of the strech can be allocated for a wider median with trees on it or for parking on the other side or for a wider sidewalk or even for bus bays. But it is important to have consistent lanes all through"
This has been developed more in the attachment.
Bus bays have been seperately provided for - pls leave that from this discussion for now.
Not that BBMP engineers don't know this. I have heard them only say, that throughput of a long channel depends on the width of the narrowest sections. In fact, a channel with changing widths (4-6-4-6 lanes) would actually produce less throughput than a consistent narrow channel (4 lanes all through) because the merges and de-merges would produce unwanted "collisions" at the points where width would change.
It is better to have 4 lanes consistently, and use the extra width for road side and traffic management amenities like "protected turns", "holding" lanes (on top of ped/biking space as needed).
Since most readers are not likely to open and read the attachment in this post, let me pull out two pictures from the PDF Suhas has shared above.
Here is the picture showing holding lane to segregate right-turn awaiting traffic from the flow. This is pretty obvious stuff to implment, it's time follow these for corridor improvement projects.
One more picture from Suhas's PDF. This one shows waiting lane to hold traffic turning left.
The extra road width can similarly be used to provide merging lane for traffic that would come in to the corridor via "free left turns".
Suhas,
Very right - 4 continuous express lanes with additional turn lane/s (at intersections) will result in much smoother & higher throughputs than 6 lanes with no provision for turn lanes.
During the previous discussion, you mentioned about 4 magic boxes that are being included on this stretch. Provision has to be made for turning traffic in way of these magic boxes too. I doubt if they are planning substantial land acquisition at /adjacent intersections to provide 8 lanes at these spots. If so, then, uniform 6 express lanes may be possible.
If there cant be land acquisition for 8 lanes at the magic boxes then considering 1 lane for exit/entry ramps the magic box is probably carrying 4 lanes only as throughfare. It then becomes imperative not to have 6 lanes all the way and then squeeze the through traffic to 4 at the magic boxes. The merge problems will haunt again. Buffer/holding lanes work best when they open up at junctions in addition to existing carriage way like in suhas illustration. That way cars in the flow pull away into spare holding space freeing up the space for through traffic. Not that one cant dedicate the third lane for exiting traffic all the way with attendant merge problems, but that the space can be used for other features like parking/ped/greenery etc while being able to maintain smooth flow.
One can always try these with markings and bollards
I dont see how we can plan a well designed road with turn lanes, etc.
But this is all the more reason to keep it to 4 and not 6 lanes. The point of the whole exercise is to emphasise fixing the geometry of the roads is more important than adding lanes.
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