Baltimore-Washington Parkway Widening Feasibility Study

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Baltimore-Washington Parkway Widening Feasibility StudyAlternatives DefinitionAlternative 4: Combination of Inside and Outside Widening of the MainlineThis alternative was initially identified to address concerns about insufficient room for widening to theinside or outside, particularly at bridge overpasses and along those sections of the B-W Parkway withnarrow medians or the absence of medians. The thought was to shift the alignment to the inside oroutside to best fit the existing total Parkway cross section creating a hybrid alternative.After some discussion, it was agreed that narrow shoulders might be allowed at locations where theAASHTO/SHA options discussed above would not fit in lieu of shifting the alignment to either side. Thiswould, however, require obtaining a design exception which is routinely granted for this type ofcondition.The team identified a limited number of areas where there is no existing median space due to thepresence of a barrier wall or bridge abutment. In these cases, any roadway widening would have to beto the outside, thus eliminating the need to evaluate a combined inside and outside wideningalternative. This generic alternative concept was thus eliminated from further consideration during thefeasibility study.Alternative 5: Use of Existing Inside and Outside Shoulders for the Third LaneThis option would convert the existing 8-foot outside shoulder in the NPS-owned portion of the Parkwayinto the third travel lane. The idea is to only add enough pavement to provide a total of threeappropriately sized travel lanes in each direction. This concept would create a curb-to-curb width of 40feet. This would only be about 5 feet wider than the existing NPS cross section.The key concern with this alternative was the elimination of shoulders. The team felt that removal ofshoulders could become a potential safety hazard on a high-speed facility such as the B-W Parkway, withvarying degrees of curvature. Therefore, this concept was dropped from further consideration duringthe feasibility study.3.3.3AlternativesSelectedforFurtherStudyandAnalysisIn summary, two alternative widening concepts were carried forward for further analysis andevaluation. They are, respectively, widening of the B-W Parkway mainline to the inside right-of-way andwidening of the B-W Parkway mainline to the outside right-of-way.For the purposes of this feasibility study, all-new pavement was assumed to be full-depth asphaltpavement to facilitate constructability and accommodate maintenance of traffic during construction aswell as minimize long term maintenance issues that have been observed in other similar facilities thathave thinner pavement sections in the shoulders. Existing shoulder pavement is assumed to be thinnerthan the existing travel lanes and will be removed and reconstructed with full-depth pavement whenadjacent to areas of pavement widening. Additional assumptions are:32 November 2012
Baltimore-Washington Parkway Widening Feasibility StudyAlternatives DefinitionIn some cases, additional pavement width beyond that shown in the typical sections was addedfor acceleration, deceleration, or auxiliary lanes. The cross slopes of the existing travel lanes willbe maintained and extended to set the finished grade of the adjacent new lane.For purposes of setting conservative limits of disturbance widened roadside ditch sections weregraded on each side of the existing Parkway, and where possible, an additional 25 feet wasadded to account for stormwater management, using environmental site design, to meet thenew Maryland Department of the Environment (MDE) guidelines on erosion and sedimentcontrol. Figures 3.1 and 3.2 illustrate the general dimensions of the resulting stormwatermanagement/MDE designs for a typical cut or fill section of mainline roadway.Figure 3.1. Roadside Grading Typical Section (Cut Slope with Ditch)Figure 3.2. Roadside Grading Typical Section (Fill Slope with Ditch)3.2WideningOptionsThe following options were developed from the two widening alternatives evaluated: NPS Outside Widening Option. AASHTO/SHA Outside Widening Option. NPS Inside Widening Option. AASHTO/SHA Inside Widening Option.33 November 2012
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Baltimore-Washington Parkway Widening Feasibility Study

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