Analyze Person Delay Instead of Vehicle Delay

In Highway Capacity Manual (HCM) traffic analysis, “person delay” is defined as the total time required to move individuals, as opposed to their vehicles, through a particular lane of an intersection. This approach to analyzing traffic through intersections is more transit- (and pedestrian-) friendly than measuring vehicle delay.

  • Calculate person delay by multiplying the highway capacity software-derived volumes for each vehicle type by vehicle occupancy (e.g., bus passengers), and then by the intersection-based average vehicle delay in each lane group
  • In the absence of bus-lane delay calculation in Highway Capacity Software, measure delay from the right-turn lane, since right turns originate from the bus lane in a typical configuration
  • Multiply person delay for people traveling in cars using the average vehicle occupancy of cars in that corridor; work trips are about 1.1 or 1.2 people per vehicle while other trip types are closer to 2.0
  • Helps give people an alternative to cars for personal travel
  • Captures the overall impact of a project and its mitigation strategies on travelers, regardless of their mode of travel
  • Creates an evaluation method that better recognizes the efficiencies of transit, potentially allowing a bus lane to be a mitigation for the traffic impacts of a proposed development
  • Helps justify transportation improvements toward transit-friendly designs
  • Calculating person-delay is not traditionally done in HCM traffic-analysis procedures, and isn’t calculated automatically by Highway Capacity Software
Where to Use It
  • The environmental-review process for proposed actions that might change the roadway capacity for surface transit (buses):
    • Any proposed action, or its mitigation, that might increase surface transit capacity (e.g., a bus-rapid-transit project that might dedicate a traffic lane exclusively to buses)
    • Any proposed mitigation that might reduce traffic capacity on a street accommodating bus service
Professional Consensus
  • The 2010 Best Practices in the Use of Micro Simulation Models report prepared by AECOM for AASHTO highlighted calculation of person delay as a desired feature of micro-simulation models
  • The 2008 NCHRP Report 618, Cost-Effective Performance Measures for Travel Time Delay, Variation, and Reliability, recommends mobility and reliability measures that include factors “using units such as persons”
  • Volume IV of the 2007 FHWA Traffic Analysis Toolbox, Guidelines for Applying CORSIM Microsimulation Modeling Software, lists person delay within its selection of potential measures of effectiveness for project analysis

This material is the product of a partnership between America Walks and Sam Schwartz Engineering. Visit here for more information on the partnership.