It would be a waste of time and money to take an Uber to get from one end of Trafalgar Square to the other. But if your destination is several miles away and yo

It would be a waste of time and money to take an Uber to get from one end of Trafalgar Square to the other. But if your destination is several miles away and your route just happens to take you through a busy block, driving will still be faster than walking because the car can reach higher speeds in less congested parts of the route. Many people who drive around in urban centers aren't really trying to get from one part of the urban center to another; they just happen to be in the same car they just drove in from the suburbs. That trip as a whole tends to be much faster than walking, and it takes quite a bit of time to park somewhere other than your destination. So if you're optimizing for speed, it can still be rational to drive all the way to your destination.