Date of Award


Publication Type

Master Thesis

Degree Name



Civil and Environmental Engineering

First Advisor

Lee, Chris (Civil and Environmental Engineering)


Civil engineering.



Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.


This study examines the effect of heavy vehicles (trucks) on entry capacity of roundabouts. The movements of vehicles were observed at 11 roundabouts in Vermont, Ontario and Wisconsin. Gap-acceptance parameters were estimated for cars and trucks separately; consistent with previous studies, it was found that critical headway and follow-up time were longer for trucks than cars. Follow-up times for truck-involved vehicle-following cases were found to be associated with central island diameter and entry angle. Gap-acceptance parameters for all entering vehicles were adjusted to a volume-weighted average of the gap-acceptance parameters for cars and trucks. Entry capacity was estimated using existing capacity models with the adjusted gap-acceptance parameters, and compared with the observed capacity at three roundabouts. The capacity models with adjusted gap-acceptance parameters estimated capacity more accurately than the models with unadjusted parameters. Microscopic traffic simulation model was also effective in representing truck characteristics and their impact on roundabout operation.