This sounds a lot like the opening couple of pages from Ben Elton's "Gridlock" - more of a comedy/satire than sci-fi. By way of an introduction it supposes a race of hyper intelligent aliens who have been watching humanity and have figured out all their most intractable problems (the middle east conflict, the rules of cricket) with ease but find themselves utterly perplexed by traffic.
Obligatory Wikipedia summary:
The novel depicts a near-future London in which traffic congestion has reached almost critical levels, such that accidents in a few key places could bring the entire city's traffic network to a halt. The government is aware of the problem and plans a major new road-building program to relieve the pressure. The alternative, heavy investment in public mass transport systems such as railways, is ignored because it clashes with the government's ideology. The author argues that this is a highly misguided policy since, in his view, more roads have historically tended to simply generate more traffic and so create an even bigger problem in the long run.
The climax of the book sees shadowy, possibly government-backed forces deliberately instigate the necessary simultaneous accidents which do indeed bring the whole of London to a standstill for several days. The resulting chaos is used as an excuse to press ahead with the road-building scheme.
See also this capture from Google Books.
