On-Road Evaluation of Emission Impacts of Roundabouts

Abstract

Reduced emissions and improved air quality are typically attributed to the use of roundabouts rather than traditional stop or signal control. Roundabouts are expected to reduce emissions as a result of reduced delays and stops. However, roundabouts slow all vehicles to speeds at which emissions may be higher, while signals stop and delay only a portion of vehicles. Roundabouts may also increase the amount of acceleration and deceleration for all vehicles. Because emissions are correlated to these modal events, their impacts should be considered in the evaluation of roundabouts. An on-road assessment of the emission impacts of two roundabouts compared with other types of traffic control was conducted with a vehicle instrumented with a portable emissions monitor. Emissions were measured along two corridors in Woodbury, Minnesota, with two drivers. The corridor at Bailey Road had two four-way stop-controlled intersections, one roundabout, and one signal. The corridor at Lake Road had one four-way stop, one roundabout, and one signal. Intersection spacing and traffic parameters were similar along each corridor. Emissions were compared for sections 750 ft upstream and 750 ft downstream of each intersection. Traffic conditions during data collection along both corridors were uncongested. Average emission rate by driver was compared for the three types of traffic control. Results suggested that emissions were highly dependent on driver behavior. The roundabouts did not necessarily have lower emissions than traditional stop or signal control.

Before-and-After Field Investigation of the Effects on Pollutant Emissions of Replacing a Signal-Controlled Road Intersection with a Roundabout

“…Considering NO (Figure 4), it is seen that signal control appears to produce always lower emissions than the roundabout. This is consistent with the findings of previous work reported in the literature; see, for example, [8,[12][13][14]. Opposite results are obtained for CO 2 (Figure 2), while for CO the roundabout is seen to be less polluting only in three out of six trip conditions (Figure 3).…”

“…Hallmark et al [14] used a vehicle instrumented with a Portable Emission Measurement System (PEMS) to collect on-road pollution data and compared the air quality impacts of different types of intersections (signal-controlled, fourway stop, and roundabout). Based on the analysis of CO 2 , CO, NO , and HC emissions, the authors concluded that roundabouts do not necessarily perform better than the other forms of intersection control.…”

“…Two data collection campaigns were conducted along Viale Mazzini, an urban corridor located in the city of Vicenza, Italy, before (April 1-3, 2014) and after (April [14][15][16]2015) the conversion of a signalized intersection to a roundabout ( Figure 1). In both cases data were collected over three consecutive weekdays (Tuesday to Thursday).…”

Identification of emission hotspots in roundabouts corridors

“…Research in the field of transportation emissions has dealt with the environmental impacts of single-lane and multi-lane roundabouts installed at isolated intersections as well as in signalized corridors Guo and Zhang, 2014;Kwak et al, 2012;Xia et al, 2012) and mixed traffic lights/roundabout corridors (Coelho et al, 2009a;Hallmark et al, 2010Hallmark et al, , 2011. Little research has been documented on traffic operations on a roundabout corridor level.…”

Evaluating Operational Performance of Intersections Using SIDRA

“…Hallmark et al (2011) suggested that roundabouts might not necessarily yield lower emissions compared to the traditional stop or signal control intersection as they found emissions are highly dependent on driver behaviour [9]. Esawey and Sayed (2013) presented an indepth literature review of existing methods to analyse the operational and the safety performance of unconventional intersection designs [10].…”