There have been some rumors that there was no serious attempt for a Western Bypass, neither an outer Beltway. Here are some links to the lobbying group which is pushing for the outer beltway.
It starts with the Tri-County Parkway , which is shown as two alternatives in the map below. If the parkway was build as option D, then the extension is BRR as outlined in the paragraph below as part of the Western Transportation Corridor WTC.
The Western Transportation Corridor is the first step toward an outer beltway.
Please see the section "Most Immediate Need". In case political climate changes in Maryland, the outer Beltway could become reality and it would go right through Ashburn. It could be very likely Belmont Ridge Road. It is also very surprising that BRR is on the CTP map as 150 feet wide, very wide for just a 6 lane road. Certainly if the political climate changes in Loudoun and all these 6 lane roads are a line on the map, all of sudden the roads are getting closer to reality.
Here are the 10 reasons why the Western Corridor should be on Loudoun's CTP. Some people believe that route 15 would be part of the outer beltway, please see section 3. which states that route 15 to be preserved as a historic road. It clearly states that the WTC would become the de facto outer beltway as shown in section 8.
Below are some build alternatives as envisioned by the lobbying group, which prefers the Western Bypass to be Belmont Ridge Road or Loudoun County Parkway: