Concrete side barriers on the shoulders can become a sight obstruction if the roadway curvature is tight and the barrier is not offset away from the travel lane to see past it. To ensure that sight distance is achieved, the roadway geometry can be evaluated for Horizontal Sight Offset (HSO). The HSO calculation utilizes the curvature of the roadway, speed design, and stopping sight distance to establish a minimum value for the distance an object should be from the travel way for sight distance to be achieved. A screening of the geometry from the 1980’s plans was performed and determined that a curve in the northbound lanes between the Courtland Street/Ralph McGill Boulevard bridge and the Peachtree Street bridge does not achieve sufficient HSO. Based on the HSO calculations, the shoulder needs to be 11 feet wide to achieve HSO; as such, the current existing condition at this curve may not achieve sufficient sight distance. In some cases, it is possible to achieve sight distance without meeting HSO. If the curve is short enough that a driver can see beyond the curve to the tangent sections of roadway on either side of the curve, sight distance can be achieved while not meeting the HSO screening criteria. Survey data and a preliminary level of design will be required before this type of assessment can be made. As the concept design is developed, this location will need to be evaluated to determine how best to accommodate sufficient sight distance. Bent construction that avoids reducing inside shoulder width on the northbound lanes and modified alignment geometry for the northbound lanes may be needed to achieve minimum sight distance requirements. This may include shifting the center bridge bent location to the shoulder of the southbound lanes and adjustments to the northbound alignment to achieve sight distance. It is very unlikely that a design exception will be approved at this location if sight distance cannot be met. Even if the proposed project retained the existing inside shoulder width, an approved design exception will still be necessary as the existing condition does not meet current standards and construction of the cap will be a constraint to the ability to correct the issue with future projects. Demonstrating that sufficient sight distance around this curve is achieved will be critical to getting an approved design exception for reduced width inside shoulders. HORIZONTAL CLEARANCE - OUTSIDE SHOULDERS Like the inside shoulders, the outside shoulders were originally designed to dimensions that meet current design standards. The 14-foot outside shoulder depicted in the 1980’s construction plans is consistent with current GDOT design standards; however, at some point between the widening of the Downtown Connector in the late 1980’s and the early 2000’s, an additional lane in each direction was added. The addition of these lanes required reduction of the inside and outside shoulders and removal of the buffer area between the HOV and general-purpose lanes. Plans from the restriping project haven’t been located, however measurements from aerial mapping indicate the existing outside shoulder withs are approximately ten feet, which does not meet current standards. Retaining reduced width shoulders or proposing construction that will further reduce outside shoulder widths to accommodate bridge abutments to support the Stitch bridge cap will require
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