Below is information from the VDOT Project Website. As one of the many sitting in traffic, I find this to be (1) on the technical side - pretty neat and (2) on the commuter side - long overdue and way too long to wait 
What's being done
Route 29/Linton Hall Interchange Improvement Project is one of the largest construction projects in Virginia. The current total estimated project cost is approximately $181.4M.
The purpose of the Phase IV - I-66/Route 29/Linton Hall Road Interchange project is to construct a grade separated interchange at the existing Route 29/Linton Hall Road intersection, creating a fully limited access facility on Route 29 between Virginia Oaks Drive and Heatcote Boulevard. The interchange will be a single point urban diamond interchange (SPUI), with a braided ramp configuration along southbound Route 29 between I-66, Linton Hall Road and Gallerher Road.
The interchange will include 4 bridges:B632 - Route 29 and Ramp K over Norfolk Southern Railroad
B633 - Linton Hall Road over Route 29
B634 - Route 55 over Norfolk Southern Railroad, and
B635 - Ramp G over Ramp K.
Also associated with this project are the removal of at-grade railroad crossings (Norfolk Southern Railroad at Gallerher Road, Route 29 northbound and southbound) and two traffic signals along Route 29. Following completion, Route 29 will be a 6-lane divided facility between I-66 and Virginia Oaks Drive and will operate without signals or obstructions within this same area.
Phase IV Plan Roll in PDF Format
Proposed Construction Phasing - Maintenance of Traffic
There are three main phases of construction - Phase 1 is broken into two parts that can be completed mostly at the same time.
Below is the preliminary breakdown of various construction phases with a rough estimated construction cost at this time:
Phase 1A - Detour Construction - $10 million - includes Route 29 & Linton Hall detour construction and temporary railroad signal crossings. Estimate construction time for this phase is 6 months.
Phase 1B - Interchange Construction - $50 million - includes Linton Hall Road bridges over 29 and NS Railroad NB 29 Bridge over NS Railroad ultimate grades of NB 29 and portions of interchange ramps, and access roads. Estimate construction time for this phase is 24 months.
Phase 2 - Interchange Construction - $30 million - includes SB 29 bridge over NS Railroad Ramp G bridge over Ramp K ultimate SB 29 grading and portions of braided ramps. Estimate construction time for this phase is 12 months.
Phase 3 - Interchange Construction - $5 million - includes final portions of Ramps I and J and minor detours to facilitate final construction. Estimated construction time for this phase is 6 months.
Estimated Total Construction Time: 4 Years
What's being done
Summary of other I-66 Projects
Phase I (UPC 63724) - University Boulevard - new alignment Construct a four-lane divided roadway with a bridge over I-66 from Wellington Road to Rte 29.
Status: Construction completed and opened to traffic on August 06.
Phase II (UPC 69113) - I-66 HOV widening from Rte 234 Business to the Rte 234 Bypass. Add one HOV and one SOV lane to EB and WB converting the existing four lane divided interstate to eight lanes divided.
Status: Construction completed and opened to traffic in November 2006.
Phase III (UPC 70043) - I-66 HOV widening from Rte Bypass to Rte 29. Add one HOV and one SOV lane to EB and WB converting the existing four lane divided interstate to eight lanes divided.
Status: Construction started on December 2006 with a completion date of August 2010.
Based on traffic counts, Route 29 carried 46000 vehicles per day (ADT - average daily traffic) in 2005, and is anticipated to increase to 63,000 ADT by 2035. Linton Hall Road's count in 1998 was at 9000 ADT, and by 2005 that number had increased to 15,500 ADT. By 2035 it is anticipated to grow to 42,000 ADT on Linton Hall Road.