When you first look at it, a old petitioner (old bag) asks you to give her shuttle service to help her get her groceries. You think “Walk, Lady.” Well, when building a city, you can increase the distance a person can travel from transport by one square by enacting this expensive ordinance. This means that if you are using the 14x14 method of building (See 14x14 blocking) you do not need to worry about sims not being to travel all the way through commercial zones. It also helps you save the maintenance costs of rail and subway stations, and saves money in the long run.
Shuttle Service will increase the distances sims can travel by the following:
Residential: 3-4
Commercial: 4-5
Industrial: 5-6
For a more complete explanation of how far sims will travel, see How Close Tiles Must Be to Transport.
