Archive Issue

April / May 2010

Transportation Issue
I-20 CD lane perspective looking east toward Wesley Chapel Road with the I-20/I-285 interchange in the foreground and the planned barrier-separated CD lanes on the right side of the I-20 general purpose lanes.

The metro Atlanta region has experienced sustained growth in the last decade and is the fastest-growing of all 361 metro areas in the nation, according to the Atlanta Regional Commission (ARC). Regional population forecasts anticipate an additional 2.3 million residents in the next 25 years, which will only further strain a transportation system that is often challenged, and sometimes beaten.
     Atlanta's trouble spots are scattered across the metro area's U.S. highways and state routes, but an area of particular concern for the Georgia Department of Transportation (DOT) is eastbound I-20 on the eastern side of the city between I-285 and Wesley Chapel Road. Because of conflicting traffic movements, a high amount of weaving, and resulting operational insufficiencies, the stretch of I-20 eastbound from I-285 to the I-20/Wesley Chapel Road interchange operates at a failing Level of Service of F in the evening rush hour, frustrating many commuters and simply denying entry to others.
    What's the main culprit of this frustration? High weaving caused by conflicting movements between vehicles trying to exit I-20 at Wesley Chapel Road and I-285 traffic trying to merge onto I-20 for destinations east of Wesley Chapel Road. This weaving more than doubles travel time from the I-285 south ramp to the Wesley Chapel Road eastbound off-ramp between the non-peak and peak periods. It also causes a significant reduction (approximately 51 percent) in vehicle throughput, leaving extensive queues and many vehicles denied entry into the system. More importantly, 75 percent of accidents in this segment are sideswipe and rear-end accidents, which are typical of areas with high weaving and heavy stop-and-go conditions. Both injury rates and sideswipe and rear-end accident rates for this section are substantially higher than state rates for comparable sections.
    To provide users of this transportation system with a more efficient, safer traveling experience, Georgia DOT identified the need for a short-term operational improvement project to address the growing problem. The project was intended to be something that could be implemented quickly with as few environmental impacts as possible to not delay environmental and federal approval. The result was a collector-distributor (CD) lane concept developed by ARCADIS for implementation by Georgia DOT on a fast-track schedule leading to a design-build contract.
    The concept calls for the addition of CD lanes, modification of general-purpose lanes, and ramp improvements to separate conflicting traffic and eliminate the problematic weaving behavior in the eastbound direction of I-20. The CD lanes, which are planned between I-285 and Wesley Chapel Road, will be separated from the general purpose lanes by a barrier system. A new deceleration lane will begin just west of the I-285 bridges over I-20, and a new slip ramp located just east of the I-285 interchange bridges will transition eastbound travelers from the I-20 general-purpose lanes to Wesley Chapel Road. Travelers on I-285 desiring to go east on I-20 will first connect to the new CD lanes before merging with I-20 just east of Wesley Chapel Road. The transition of the new CD lanes to existing general-purpose lanes will occur between the Wesley Chapel and Panola Road interchanges with I-20. In addition, the on ramp from Wesley Chapel Road to I-20 eastbound will be improved to provide a longer lane for merging.
    Additionally, engineers designed the entire CD lane concept to be constructed inside existing right-of-way using advanced retaining wall technology to reduce environmental noise impacts. Because no new right-of-way would be required, no existing commercial or residential properties would be displaced. ARCADIS' ecology department streamlined the Nationwide Permit application process with the NEPA process, and the project is anticipated to be approved by the Federal Highway Administration (FHWA) as a Categorical Exclusion with no right-of-way or significant environmental impacts.
    With the addition of this CD lane, conflicting and weaving vehicle movements will be significantly reduced. The segment of I-20 from I-285 to Wesley Chapel Road will experience a 93 percent increase in vehicle throughput, and the segment of I-20 from Wesley Chapel Road to Panola Road will experience an 84 percent increase in throughput. Over the whole section, vehicle hours of delay will be reduced 60 percent from 1,630 hours to an estimated 635 hours of delay. More importantly, the need for weaving will be essentially halved, leading to more efficient traveling conditions, higher speeds, fewer accidents, and less delay; for commuters and freight traffic who travel this corridor daily, that equates to safer conditions, less time spent in stop-and-go traffic, more consistent commute times, and an overall higher quality of life.
    The goal of this project is not to completely fix the operational deficiencies of this interchange, but to renew and extend the operational life of a critical segment of Georgia's interstate system. By implementing a design-build strategy to effectively and efficiently manage resource allocations and schedule, and by streamlining the nationwide permit application process with the NEPA process, the Georgia DOT, FHWA, and ARCADIS teams plan to capitalize on an early implementation phase to solve an immediate problem while keeping an eye on the future. This CD lane concept was developed not only to deal with an emerging safety and operations issue, but also to be easily incorporated into long-term solutions as planned in ARC's Regional Transportation Plan.
    Funding and a lack of resources have pushed many major transportation system overhauls into the far future, but projects such as this fast-track CD lane concept show that in a world of shrinking funding and limited resources, timely, short-term fixes are not impossible. All it takes is a little strategic innovation.