asj - 23 January, 2009 | Traffic | Junctions | Police | Pune | indian | Pune | Congress | Cops | Analysis | Road | PMC | signals

Here is how data is mis-interpreted and mis-used to suit one's belief systems:

Below is a letter I wrote to the journalist who did this TOI feature -

I am writing with regards to your feature 'Cops look at solutions to smoothen traffic flow' published in Time of India on 18 jan 09 http://timesofindia.indiatimes.com/Cities/Pune/Cops_look_at_solutions_to_smoothen_traffic_flow/articleshow/3995212.cms.
 
I trust that TOI will publish a counter argument to proposals suggested by DCP Patil as the solutions considered by his office are contrary to scientific reasoning. 
 
The two points I would like to contest are pertain to -

1. Using Mumbai's goegraphic size and number of traffic signals as a bench mark for deciding the number of traffic signals in Pune
2. Suggestion that allowing vehicles to ply at higher speeds increases 'road space' i.e. capacity.

Counter-arguments to point 1: 
 
The article says that Pimpri-Chinchwad put together have as many as 235 traffic signals in an area of around 410 sq km, which is two more than the number in Mumbai, which covers an area of 603 sq km. Further this becomes a justification to removal of traffic lights - a policy that has been implemented increasingly in recent months. This logic has many faults elaborated below -

1. Mumbai may well have 603 sq km, but 20-25% of this is consumed by the Sanjay Gandhi Borivali National Park.
2. Mumbai has many more open spaces than Pune (parks and playgrounds like Azad Maidan, Cross Maidan, Shivaji Park, etc). Add to this Asia's largest slums (Dharavi alone is 175 hectares) as well as several textile mill land and another 10-15% of 603 sq km will be taken out of equation.
3. Above points in itself demonstrate the faulty logic of Pune police - as Mumbai does not actually have more space. In all probability the area of Mumbai and Pune is similar and it makes perfect sense that the two cities have more or less similar number of traffic lights.
4. Being a costal city - a significant number of roads have virtually no junctions. Examples abound but a few worth mentioning are - Marine Drive, Haji-Ali, Worli sea face, Road along Mahalaxmi Race course, roads along Azad maidan, Cross Maidan, Shivaji park - the list is endless. This is another reason why Mumbai is likely to have less signals.
5. More importantly, road layouts, number of junctions along with the vehicular (and pedestrian) density at each junction and accident history should inform whether there is a need for traffic signals or not. Indian Road Congress has published clear norms in this matter (I have published this elsewhere on Praja).
6. Given that the IRC norms demand consideration to vehicular densities in determining where signals are placed, Mumbai is also better placed by virtue of the fact that 88% of Mumbai citizens use buses and trains. In contrast, 80% of Pune citizens are forced to use personal vehicles due a complete lack of proficient public transport system. If 60% of Pune could use public transport, the number of vehicles on roads will go down dramatically and many junctions won't meet the IRC criteria for implementation of traffic signals. On other hand, if 80% of Mumbai 60 million were to use personal vehicles, perhaps the number of traffic lights in Mumbai may double!!
7. Where vehicle density is high, conflict at junctions' causes delays and increases risk of accidents and traffic lights helps solve both these issues. This is the fundamental reason for using signals. Signals are not used to hinder traffic flow, instead by evening out gaps in traffic - safety and flow both improve.

Counter-arguments to point 2:

The logic that allowing higher speed increases road capacity and allows more people to complete their journey in less time is incorrect. In fact the exact opposite is true for congested roads. This is because vehicles do not come to a halt instantly and a safe gap needs to be kept between two vehicles when in motion. It takes 40 feet before a vehicle stops when traveling at 32 km per hour. It takes 120 feet at 64 km per hour. Thus when vehicles trvel faster they have to be separated by wider distances to avoid accidents. Simple caluculation thus can prove that a 1 km long road with speed limit of 32km has capacity to carry 82 vehicles while at double the speed it will carry only 27 vehicles. By allowing more vehicles at more speeds travel becomes less reliable and accidents increase - this leads to more delays than at lower speeds. It is for this reason that worldwide, variable speed limits are in use on modern roads (when number of vehicles on a road increases, speed limit is more restrictive).
 
In conclusion, Traffic Police in principle should prioritise safety of citizens (pedestrians and drivers both) first. Safety and enforcement of law (rules of the road) is their prime responsibility rather than getting preoccupied with improving speed of travel (how exactly does this become a policing responsibility as this is a job of traffic planners in PMC). 

ASJ

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