There are 127 entry points into Delhi from the three neighbouring states of Haryana, Rajasthan and Uttar Pradesh. Anything between 22,000 and 38,000 trucks use these entry points every night - the lower being the official figure. The consequence of a penalty being levied on these vehicles on traffic conditions can be imagined. Given that internal combustion engines emit considerably more when idling in traffic than otherwise, it is far from clear how much of a net positive for the air the collection of this tax by contractors would be. It is unfortunate that clear studies on this question were neither worked on nor apparently presented to the NGT and the Supreme Court.
It is worthwhile to remember that, even if trucks are the major contributor to Delhi's air pollution, then those that transit through the city do so because they have no option. The government of Delhi and those of the neighbouring states have been extremely dilatory when it comes to completing the much-needed road bypass network. That will ease the nightly pressure on Delhi's ring road system. A basic economic fact is elasticity: if trucks have only one way to traverse from the south of Delhi to the east, or down from the north, then they will be forced to take it, even if they have to pay the mandated penalty. In other words, there is an inelastic demand for transit through Delhi, and imposing a tax on this would merely raise overall costs without changing the behaviour of the trucks. The only social utility, therefore, would come from the use that the Delhi government puts to the additional revenue it receives from the trucks and light commercial vehicles. Given that the Delhi government does not exactly face a funds crunch - it is very comfortably off - any public transport failure that the city faces is a product not of the paucity of funds but of imagination and planning. The priority should be to complete the road bypass network in a timely manner; the new tax is unlikely to solve the problem.