My personal experience is that a lot of books and brochures are placed with the carts. In our territory we use two locations for the carts. One is near a high school and university the other one is on a busy open-air citymarket.
people approach the carts and decide themselves if they would like to take some literature. If they take something it is because they really want it.
Young people often take the Young People ask books and brochures on creation. At the market it is more bible teach books that are taken.
If i compare two hours door to door work with two hours with a cart i must say from my own experience that the two hours with a cart yield better results. When going door to door most people that are visited are not interested. But every time i am with a cart i have spoken with a number of people that show interest and approached me instead of the other way around and decided to take some literature.
In the back of the cart we keep a notebook and write down all experiences and placements and so i can see that others have the same experience when using the cart