4.76 Suppose the roads of a city form a $(n-1) \times(n-1)$ grid. The city plans to open several bus routes, with the requirement that each bus route turns at most once, and that from any of the $n^{2}$ intersections, one can reach any other intersection with at most one transfer. How many routes does the city need to set up at a minimum?
[Solution] Since each bus route turns at most once, each route can pass through at most one east-west street and one north-south street. According to the given information, the city has $n$ east-west streets and $n$ north-south streets, with each street having exactly $n$ intersections. If each east-west street has at least one route, then there must be at least $n$ routes. If a certain east-west street has no route passing through it, then since each route that runs north-south through this east-west street only passes through one intersection on this street, at least $n$ routes are still needed to cover all $n$ intersections on this east-west street. Therefore, there must be at least $n$ routes.

On the other hand, $n$ routes can be set up as follows: let the $i$-th route bus travel from north to south along the $i$-th north-south street, turn west at the southernmost east-west street, and continue along this east-west street to the southwest corner. It is easy to verify that these $n$ routes meet the requirements of the problem.
In summary, the minimum number of routes that need to be set up is $n$.