Why travel?
Work, school, freight, service?
Transport demand begins with spatially separated activities.
Side 68
Transportation
Systems
A study of how people and goods move through constrained networks. Transportation systems connect demand, infrastructure, capacity, scheduling and behavior to travel time, accessibility, cost and reliability.
demand→network→capacity→flow→service
06system lenses
05congestion ideas
05accessibility questions
68Side
Transport demand is derived from activities.
Trips happen because people and firms need to reach work, services, customers, suppliers and destinations.
Where does movement begin and end?
Spatial pattern.
Land use and economic geography shape trip distribution.
Which transport option?
Walk, car, rail, bus, bike, air?
Cost, time, reliability and access influence mode choice.
When does demand occur?
Peak or distributed?
Temporal concentration creates capacity pressure.
How does behavior adapt?
Route, departure time, destination?
Travel demand changes when prices, congestion or infrastructure change.
Transportation is a spatial network problem.
Nodes, links and transfer points determine reach, redundancy and route choice.
Intersection, station, terminal, port.
Nodes connect routes and often concentrate transfer delays.
Road, track, lane or corridor.
Links carry finite flows at specific speeds and capacities.
Sequence through the network.
Travelers choose among paths based on generalized cost.
Change vehicle or mode.
Transfers add walking, waiting and uncertainty beyond in-vehicle time.
Alternative paths preserve movement.
Network resilience improves when critical flows have substitutes.
Local streets to trunk corridors.
Different links serve access versus movement functions.
Congestion is a nonlinear capacity phenomenon.
As flow approaches practical capacity, small demand increases can produce large delay.
Capacity
Maximum sustainable flow.
Geometry, control, vehicle mix and incidents all affect practical capacity.
Density
Vehicles per unit distance.
Higher density eventually reduces speed and flow.
Queue
Demand exceeds discharge rate.
Queues store delayed travelers in space and time.
Bottleneck
One constrained segment governs flow.
Expanding capacity elsewhere may not improve end-to-end performance.
Induced demand
Capacity changes behavior.
Lower travel cost can attract new trips, routes, destinations or development patterns.
Transit trades fixed service structure for shared capacity.
Frequency, reliability, stop spacing and network integration determine how useful service feels to riders.
| Variable | Question | Trade-off |
|---|---|---|
| Frequency | How often does service arrive? | Operating cost vs waiting time |
| Stop spacing | How often does the vehicle stop? | Access vs speed |
| Capacity | How many passengers can move? | Vehicle size/frequency vs cost |
| Reliability | Does service arrive predictably? | Recovery time vs utilization |
| Transfer design | How easily do routes connect? | Network breadth vs directness |
Freight systems move value through time and space.
Mode choice depends on shipment size, value density, urgency, reliability and terminal access.
Flexible network reach.
Strong for door-to-door movement and shorter or variable routes.
Efficient heavy corridor movement.
Best where large volumes justify fixed network access.
Low unit cost at massive scale.
Slow transit and port dependence favor less time-sensitive cargo.
Speed for high-value goods.
Cost and capacity constrain use.
Combine mode strengths.
Containers reduce handling cost across ship, rail and truck.
Transfers can dominate delay.
Ports, yards and warehouses are nodes where congestion and synchronization matter.
Mobility is not the same as accessibility.
A fast network is useful only insofar as it connects people and goods to valued destinations.
Opportunity
Count jobs, services or destinations reachable within a time/cost budget.
Travel time
Measure door-to-door time rather than vehicle speed alone.
Reliability
Uncertain arrival can be more costly than slightly longer predictable travel.
Affordability
Financial cost constrains effective access.
Coverage
Network reach determines who can use the system at all.
Transportation Engineeringtraffic and infrastructure foundations
Urban Transportation Networksnetwork assignment and flow
Public Transportation Systemstransit operations
Transport Economicsdemand, pricing and externalities