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Report: Current design would lengthen travel time through bypass interchange
Sean Tubbs | Saturday, March 09, 2013 at 5:22 p.m.

Traveling through the interchange on the southern end of the proposed Western Bypass would take motorists almost three times longer under the current design compared with the original, according to an internal report on the project.

Using an elevated ramp -- a so-called flyover, part of a 1997 design -- a truck traveling 45 mph would cover the interchange in an average of 58.3 seconds, compared with two minutes and 47 seconds using an off-ramp and intersections with signals at Leonard Sandridge Road, according to the report.
 
The latter option was proposed by the joint venture of Virginia Beach-based Skanska-Branch, which submitted the low bid for the project at $136 million and was awarded a contract in June. A $192-million bid submitted by Zachry/TranSystems of San Antonio included a flyover ramp consistent with the '97 design.
 
“As would be expected, the flyover is the best from a traffic operations perspective,” Parsons Brinckerhoff engineer Mike Fendrick wrote in a November draft memo to the Virginia Department of Transportation.
 
The Federal Highway Administration requires what's known as an “interchange justification report” when VDOT plans new interchanges in the federal highway system. 
 
That is separate from the environmental assessment VDOT is conducting to receive federal approval to proceed with final design and construction of the 6.2-mile, four-lane bypass.
 
The highway administration can either approve construction or require additional environmental study. No timetable for a decision has been made available.
 
Skanska-Branch's bid was the lowest among the seven firms that responded to a request for proposals to design and build the Western Bypass.
 
To justify the interchange design, VDOT must evaluate alternate configurations of the southern terminus, as well as the northern end at Ashwood Boulevard.
 
Two preliminary reports developed by Parsons calculated the travel times for both cars and trucks through the southern terminus from Old Ivy Road heading north onto the bypass. The findings were almost identical.
 
In the Skanska-Branch design, motorists would almost immediately exit U.S. 29-250 via a ramp to Leonard Sandridge Road. After a left turn, motorists would head north, crossing over U.S. 29-250 on a bridge with an 11-percent grade.
 
Other alternatives configured as part of the interchange analysis include a “diverging diamond” and a partial cloverleaf.
 
Travel times in each of the alternatives would be faster than in the Skanska-Branch design, according to the data from Parsons Brinckerhoff.
 
The highway administration weighs in on interchange designs in order to address potential traffic congestion known as "weaving."
 
”Weaving is a conflict that occurs when traffic streams on a highway cross at high speeds due to one traffic stream trying to get off the highway at an interchange while another is trying to get on,” said Stephen Williams, executive director of the Thomas Jefferson Planning District Commission.
 
Williams said a project known as the "Best Buy ramp" will reduce an existing congestion point on the U.S. 29-250 Bypass between Emmet Street and the Barracks Road interchange. In his analysis, Fendrick said the Skanska-Branch design might worsen existing conditions.
 
“There is an operational issue on the US 29/250 freeway between Ivy Road and the proposed interchange,” Fendrick wrote. “Due to restrictions at the Old Ivy Road bridge, railroad bridge and Ivy Road bridge, the merge lane cannot be lengthened.”
 
American Infrastructure, a Pennsylvania-based contractor that submitted a $139-million proposal, filed a protest in June claiming the Skanska-Branch design did not meet VDOT’s requirements to address weaving.
 
“We maintain that a more comprehensive interchange configuration at the southern terminus of the proposed bypass is required,” wrote J. David Nardon of American Infrastructure in a June 13 letter to VDOT after the agency denied the protest.
 
Highway administration officials reviewing the Skanska-Branch design will consider several factors, including "overall benefits, overall system-network performance and possible mitigation strategies,” said Doug Hecox, a spokesman for the agency.
 
The highway administration's review of the interchanges won’t begin until the environmental evaluation is completed.
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