How do contact and non-contact forces affect the design of different modes of transportation?

Contact and non contact forces are big factors to consider in designing of different modes of transportation because this factors are resistances for the mode of transportation. These contact and non - contact forces should be minimized in order for the energy requirement to be also minimum. But not the extent of risking the safety, for example a non contact force is the wieght, the should be optimum, safety of the design should not be compromised just to reduce weight, just like by removing essential parts, support just to remove weight is not good.