12.3 Other Modes
While roundabout analysis is mostly limited to the vehicular methodology, there are some considerations available for roundabout analysis of pedestrians and bicycles. These methodologies are generally described in this section and are described in detail in the HCM, NCHRP 616, NCHRP 834, and Mineta Transportation Institute Report 11-19. For more information on multimodal analysis, see
Chapter 14
.12.3.1 Pedestrian
High volumes of pedestrians at a roundabout may warrant the need for a LOS analysis, which may be conducted using the guidance found in HCM 7th Edition, Chapter 22, or NCHRP 616, Chapter 8. The methodology in NCHRP 834, Chapter 7 may also be used as an alternative method of analyzing pedestrian crossing needs, (e.g., need for PHBs at a roundabout). Even in situations where high volumes of pedestrians are not consistent at a roundabout, it is common for a few pedestrians or groups of pedestrians to sporadically interrupt vehicular traffic. Junctions (ARCADY: Assessment of Roundabout Capacity and Delay) or Microsimulation (microscopic) analysis may be used to model the interactions in this scenario. Microsimulation can provide valuable visual and numerical insights on how pedestrians interact with and impact the operations of a roundabout.
An alternative method of multimodal analysis is based on bicycle level of traffic stress (BLTS) and may be applied to pedestrian analysis at a roundabout. The pedestrian level of traffic stress (PLTS) methodology classifies the roundabout into one of four walkability categories. Each of these categories is based on perceived safety issues near the roundabout rather than pedestrian LOS. Characteristics that affect level of traffic stress are sidewalk existence, condition and widths, buffer between the sidewalk and the road, and roadway speed. A level of traffic stress score of 1 indicates that the roundabout is suitable for most pedestrians; a level of traffic stress score of 4 indicates that only able-bodied pedestrians may attempt to cross the roundabout. This methodology is based on the Mineta Transportation Institute, Report 11-19. See
Chapter 14
of this manual for more information. Additional analysis methods can be found in NCHRP Research Report 992: Guide to Pedestrian Analysis. It presents a state-of-the-art guide to conducting pedestrian traffic analysis on the basis of volume, safety, operations, and quality of service.12.3.2 Bicycle
Bicyclists can either use the vehicular travel lanes or the pedestrian sidewalk to traverse the roundabout. In instances where large volumes of bicycles are anticipated to use the sidewalk to traverse the roundabout, slip ramps can be integrated into the roundabout to accommodate the transition from road to sidewalk. When bicycles traverse the roundabout on the road, they are analyzed for capacity similarly to other vehicular traffic. Conversely, when they traverse the roundabout on the sidewalk, they are analyzed as pedestrians. The volume of bicycles that enter the roundabout on the road are included in the vehicular volumes when analyzing roundabouts with the motorized vehicle methodology.
For bicycle LOS analysis, refer to HCM 7th Edition, Chapter 22, or NCHRP 616, Chapter 7.