Traffic Flow Patterns - Analytics
Overview
Section titled “Overview”Modelling Congestion and Volume-Capacity Ratios
Section titled “Modelling Congestion and Volume-Capacity Ratios”The primary use of traffic flow patterns is to estimate hourly traffic flow levels from Annual Average Daily Traffic (AADT) data to perform congestion analysis.
- Flow Calculation (Qp): HDM5 calculates the traffic flow in Passenger Car Space Equivalents (PCSE) per hour for each period.
- Volume-Capacity Ratio (VCRp): For each flow period, the system determines a volume-capacity ratio, which is the ratio of that period’s traffic flow to the road’s ultimate capacity.
- High-Flow Focus: Particular attention is usually paid to highest-flow hours (peak periods) by dividing them into shorter periods, as congestion delays and costs are greatest during these times.
Impact on Road User Effects (RUE)
Section titled “Impact on Road User Effects (RUE)”HDM5 performs technical analyses for every vehicle type (k) under the specific conditions of each traffic flow period (p):
- Congested Speeds: The VCRp for each period is used to calculate steady-state congested speeds and vehicle operating speeds (SSkp).
- Acceleration Noise: Traffic interactions in each period are modeled using “acceleration noise,” a measure of speed change severity. This combined noise (natural plus traffic-induced) is used to calculate additional resource consumption.
- Resource Consumption: Quantities for fuel, oil, tyres, and parts are calculated for each vehicle type within each specific flow period before being aggregated.
- Emissions and Energy: Quantities of exhaust emissions and energy consumption are also computed separately for each vehicle type and traffic flow period.
Annual Aggregation
Section titled “Annual Aggregation”After calculating the effects for each period, HDM5 aggregates the results into annual totals or weighted averages for each vehicle type using the following general logic:
- The system multiplies the results from each period (e.g., speed or fuel use) by the proportion of annual traffic (HVp)and the number of hours (HRYRp) that period exists, then sums them up.
- This results in annual average operating speeds and total annual road user costs.