Waheed Uddin, PhD., P.E.Professor and Director, CAIT

Center for Advanced Infrastructure Technology Department of Civil Engineering

The University of Mississippihttp://www.olemiss.edu/projects/cait/Index.html

Performance Evaluation of Roundabouts for Traffic Delay and

Crash Reductions in Oxford

M I S S I S S I P P I D E PA RT M E N T O F T R A N S P O RTAT I O N

S TAT E S T U D Y 2 1 3

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Task 1 ─ Collect and Review Pre-roundabout Data Historical traffic and historical crash data – Provided by MDOT Prior studies –Traffic and Planning Studies (Completed by Neel-Schaffer on behalf of MDOT) Plans - (Provided by MDOT)

Task 2 ─ Collect and Analyze Post-roundabout Data Current available traffic and crash data – Provided by MDOT On-site traffic data collection – completed by engineering students Traffic analysis of current traffic data – completed by Graduate student

Task 3 ─ Conduct Road Users’ and Public Survey Anonymous on-site and telephone surveys

Task 4 ─ Submit and Present Interim Report Task 5 ─ Finalize Data Collection, Complete Analysis, and Evaluate Results Task 6 ─ Final Report

Project Overview

The overall goal of this study is to assess the performance of a double roundabout interchange at the South Lamer Boulevard Exit on Highway 6 with respect to traffic

flow, capacity, safety improvements, benefit/cost, and public opinion.

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Highway 6 and South Lamar Avenue Interchange

Prior to the roundabout construction the interchange experienced extreme delay, was a safety concern, and was projected to exceed capacity limitation by 2016.

Planned roundabouts on South Lamar Blvd.

(courtesy of James Sullivan, MDOT)

Current roundabout on South Lamar Blvd.(Google Earth)

The signalized and stop controlled intersections were replaced with a double

roundabout interchange, a full roundabout on one side and a teardrop shape on the other.

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Total VPH North Bound

Total VPH South Bound

Total VPH

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Traffic DataIntersection of Hwy 6

Ramps and South Lamar Avenue

Collected by The University of Mississippi Engineering Students

Dates of Collection: October 12 – 17, 2009

Collection time: 7:00 AM to 7:00 PM

Collection intervals: 15 minute

Vehicle Class Distribution: Motorcycle, Truck, Bus, Passenger Car

Delay and Speed Results Queuing Results

Traffic Analysis Resultsfrom microsimulation software

Environmental Impacts of Roundabouts Decrease in vehicular

emissions and fuel consumption by reducing idling time at intersection

Vehicles stopping at traffic signals and stop signs emit more CO2 when compared to vehicles at roundabouts as the delay and queuing are greater

When vehicles are idle in a queue they emit about 7 times as much CO as vehicles traveling at 10 mph. The emissions from a stopped vehicle are about 4.5 times greater than a vehicle moving at 5 mph [environmental impacts of modern roundabouts]

Air Pollutant Stop - Controlled Intersection Roundabout IntersectionVOC emissions (g/hr) 6,030 1,399CO emissions (g/hr) 89,535 20,779

NOx emissions (g/hr) 4,484 1,041PM10 emissions (g/hr) 439 101

Air Pollutant Emissions For Pre- and Post - Roundabout*

* Emission values based on traffic data and speeds from Microsimulation Software.

g/veh/miEmission Rates by Speed and LOS for Light-Duty Vehicles and Trucks

25 Contact Points 7 Contact Points

What Makes Roundabouts Safer?

Stop Controlled Intersection

Roundabout

• Less Contact Points• Lower Travel Speeds• Geometry

• Calmer Drive

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Crash Data for the Highway 6 and South Lamar Intersection

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AM and PM Crash DataCrash Reduction Pre- and Post- Roundabout

Crash data for Highway 6 and South Lamar Interchange

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Average Number of Crashes per Half a Year Pre- and Post- Roundabout

JH_Oxford_Crash_Data_SL.xls Jessica Headrick_9.11.09

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Post- Roundabout

The t-test concludes that the installment of the roundabouts do have a significant effect on the number of crashes reduced.

Daytime crashes were significantly reduced in the first year of the roundabout opening to traffic.

Public Opinion Survey

Locations of collection: On-site at two convenience

stores adjacent to the roundabouts

Random telephone and e-mail surveys

Factors: Age

Familiarity

Favorability

Results showed overwhelming approval of the roundabouts and support construction of more roundabouts.

Respondents commented…to install improved signage including flashing lights and additional pavement markings, especially at the south roundabout.

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Performance Analysis of Roundabouts

Since the replacement of the signal controlled interchange with the roundabout interchange:

Driver delay has reduced by 24%. Driver idling time has reduced by 77%. Driver fuel wastage has reduced by 56%. Travel time through the interchange has

increased by 67%, saving drivers approximately $806,018 annually*.

Crashes and crash related injuries have been significantly reduced savings an annual comprehensive cost of $86,008 U.S. dollars.

Drivers favor the roundabouts over the signalized intersections at this location.

*Annual total of all vehicles through the interchange.