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Traffic models flag PM pressure on Monument Drive and other corridors; staff point to signal tweaks and a possible Government Center–mall crossing
Summary
Fairfax County staff presented travel-demand modeling showing volume-to-capacity increases in PM peaks on Monument Drive, Post Forest Drive and parts of Fairlakes Parkway; staff said intersection-level analysis and signal timing changes are first mitigation options, and a costly Government Center extension across I‑66 could help disperse trips.
Fairfax County transportation staff reported to the task force on April 6 that future land-use scenarios increase volume-to-capacity (V/C) ratios in several Fairfax Center corridors, particularly during the evening (PM) peak.
"A volume-to-capacity ratio approaching 1.0 means you're approaching congested conditions," said Thomas Burke, who presented travel-demand model results comparing existing conditions, baseline adopted land uses and the task force's preferred land-use scenario.
Burke said existing conditions show some PM peak congestion on Monument Drive and Waples Mill Road where segments are approaching capacity; under both the baseline and the task force's preferred scenario, PM peak conditions worsen in the core area with Monument Drive showing prominent red/yellow segments in the model output. Post Forest Drive and a short stretch of Legato in front of the county office also appeared to approach or exceed desired V/C thresholds in modeled scenarios.
Staff stressed they will next analyze intersections (Synchro or similar) to calculate delays and to identify targeted mitigations. "We're going to have to look at intersection operations and see where some of these issues could be mitigated," Burke said, noting that signal-timing adjustments and small operational fixes often can improve throughput without adding lanes.
Task force members cautioned about trade-offs: speeding traffic is harmful to pedestrians, and signal timings that prioritize vehicle throughput can shorten pedestrian crossing windows. Burke said staff will include pedestrian impacts in signal-timing analyses and report recommended green-time splits at the next meeting.
A recurring mitigation idea raised by staff and members is a Government Center Parkway extension across I‑66 to the mall ring road to provide an alternative north–south connection and spread traffic off Monument Drive. Participants noted such crossings are costly and may require major reconfiguration of express-lane ramps; staff said the crossing remains a possible long-term option to explore but would require further engineering and funding analysis.
Burke emphasized a cautious approach to mitigation: the FCA area was "overplanned" with wide roads in past decades, and staff do not want to "overmitigate" by adding lanes that would undermine pedestrian and cycling goals. Instead, staff will attempt to identify modest interventions and intersection fixes that achieve desired multimodal outcomes.
Next: staff will present intersection-level results and potential signal/small-scale mitigation options at the April 27 task force meeting.
