Evaluation of Heavy Vehicles on Capacity Analysis for Roundabout Design

Roundabouts are growing in popularity across the United States. They are advantageous in intersection design for several reasons, the most compelling of which is their improved level of safety at intersections. As they become more common, it is important to be able to design a roundabout to the projected demands of an intersection and have it perform as expected. This requires not only a reliable system of calculations to determine flow rates from the roundabout’s physical parameters, but also substantial statistical data to show the effects of parameters such as driver behavior characteristics and vehicle type (Isebrands and Retting). Heavy vehicles have a much larger effect on the flow of a roundabout than a passenger car, and therefore they must be accounted for in the design (Transportation Research Board). Very few studies have looked at the effect of heavy vehicles on the flow of a roundabout. In Chapter 21 of the Highway Capacity Manual 2010, roundabouts are addressed and a passenger car equivalent (PCE) factor of 2.0 is suggested for all heavy vehicles (Transportation Research Board). The purpose of this research is to study the passenger car equivalent factor for heavy vehicles. Experience suggests that heavy vehicles, particularly semi-trucks, have a greater impact on a roundabout than two passenger cars in urban areas. It is expected that the impact of heavy vehicles on the functionality of the roundabout will vary with demand. The objective of this research is to provide support for the current 2.0 PCE or determine new heavy vehicle equivalence for the design of roundabouts. The data supported the hypothesis that the 2.0 PCE might be too low and a weighted average passenger car equivalent of 3.37 was calculated for the roundabout. This value is considerably (69%) higher than the given value of 2.0 in the current design manual.


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Tables;
  • Pagination: 6p

Subject/Index Terms

Filing Info

  • Accession Number: 01628891
  • Record Type: Publication
  • Report/Paper Numbers: NEXTRANS Project No. 180TUY2.2
  • Contract Numbers: DTRT12-G-UTC05
  • Created Date: Jan 25 2017 4:51PM