Traffic Flow Analysis
Definition
Traffic flow analysis studies how vehicles move through networks—speeds, volumes, densities, and queuing—using sensors, floating-car data, and models. It quantifies level of service, identifies bottlenecks, and tests interventions like signal timing, ramp metering, and lane additions. GIS integrates spatial context—land use, access points, and street hierarchy—to interpret causes and impacts.
Application
Cities tune signal coordination, transit priority, and bike lanes; freight planners schedule deliveries; event managers plan ingress/egress; and safety teams evaluate conflict points.
FAQ
How do fundamental diagrams relate speed, flow, and density?
They show that as density rises, flow increases to a point and then collapses; understanding this guides strategies like ramp metering and variable speed limits.
What is the value of probe data versus fixed sensors?
Probes provide broad coverage and travel times; fixed sensors deliver precise counts and lane-level detail. Combining both yields robust insights.
How should signal timing projects be evaluated?
Before–after studies with control corridors, travel time surveys, and queue length observations demonstrate real improvements beyond model predictions.
When does induced demand complicate capacity expansions?
Added lanes can attract new trips, eroding benefits; scenario analyses should include land-use feedback and mode shifts.