The Capabilities And Efficient Operation Of Several Types OfTransportation Systems Are Studied. For Highway Traffic The Main Emphasis Is OnCongestion And Its Consequences. Queuing Models Are Used To DetermineFluctuations In Waiting Time For Two Cases, The Flow Of Cars Through AnIntersection And The Passing Of Slower Cars By Faster Cars On A Two-LaneHighway. The Results Of These Studies Are Incorporated Into A Non-Linear ModelOf Highway Traffic Behavior On A Road Network. The Capacities Are Expressed ByThe Relationship Between Traffic Flows On All Routes And The Costs EncounteredOn Each As A Result Of These Flows. Highway Traffic Demands Are The Result Of AGreat Many Individual Decisions About Destination, Routes, And PreferredSpeeds. The Analogy Between Highway Traffic Equilibrium And The Market ResponseModels Used By Economists Is Given. If The Individually Incurred Cost OfTransportation Is Regarded As The "Price" In The Transportation"Market," The Economist's Demand Curve Becomes Applicable. For ASingle Road It Gives The Flow Of Traffic Demanded For Any Given CostEncountered On That Road. Generally, The Higher The Cost, The Smaller The Flow.Considering A Road Network The Demand Function Gives The Flows On Each Route InResponse To A Set Of Transportation Costs Along These Routes. EquilibriumExists If The Flows On All Roads Resulting From These Costs Are The Same As TheFlows That Produce These Same Costs. This Concept Is Applied To A Study OfTraffic Equilibrium And Use Of The Analysis In The Prediction Of Traffic FlowsIs Discussed. The Analysis Of Demand And Of Equilibrium Recognizes That FreedomOf Choice Is Part Of The Service Rendered By The Road Network. Tolls From TheUsers Of Congested Roads At Rates That Would Measure The Cost To Others CausedBy The Average Road User Would Encourage Better Use Of The Highway System.There Are Observations On How Closely Maximum Efficiency Can Be Approached ByProper Choice Of Rates On Present Toll Roads And By Other Ways Of PenalizingAdditions To Traffic Congestion. Because Of The Nonlinear Relationship BetweenUse And Cost, Such Pricing Does Not Necessarily Produce Revenues Equal To TheTotal Cost Of Operating And Financing The Individual Facility. SomeObservations On The Question Of Criteria For Extensions Or Improvements Of TheNetwork To Relieve Congestion Are Given.