An updated plan for improving the intersection of Chain Bridge Road and Eaton Place was presented to the Fairfax City Council on Feb. 7, 2023.

1. City Council Work Session
February 7, 2023

2.  Project Introduction
 Key Metric Definitions
 Existing Conditions Summary
 Project History Review
 Community Engagement Summary
 Current Alternatives Analysis
 Recommendations & Next Steps
2

3. 3
Chain Bridge Road – Rte. 123
N
Existing Traffic Signal
Proposed Traffic Signal
by VDOT I-66 Project
To I-66
To Rte. 50

4. 4

5.  Major Intersections
◦ Traffic volume measured as Annual Average Daily Traffic (AADT)
 Safety
◦ Conflict points
◦ Crash history
 Operations
◦ Level of Service
◦ Delay
◦ Queues
 Access Management
◦ Intersection spacing – Why does it matter?
5

6. 6
Evaluating Conflict Points & Safety
 Intersections are planned points of conflict
 A conflict point is any location where the paths
of road users coincide (diverge, merge, cross)
 Reducing conflict points increases safety
 Angle (merging/crossing) conflict points
generally lead to angle crashes
Image: Typical 4-way intersection
has 32 conflict points (FHWA)

7. 7
Angle Crashes are Most Frequent Nationwide
 Result in more fatalities and injuries than other crash types
 Are most frequent at the Rte. 123 – Eaton Pl. intersection
 Focus of analysis & evaluation of options
Crash Type
Fatal Injury PDO
Angle 46% 39% 28%
Rear End 18% 44% 46%
Sideswipe 7% 10% 21%
Head On 28% 7% 2%
Other/Unknown 1% 1% 2%
Crash Severity
Crash Type
2019 NHTSA Traffic Safety Facts Annual Report
Vehicle vs. Vehicle Crashes Only (Nationwide)

8. 8
N
A metric (letter grade) to grade operations
 Abbreviated “LOS”
 Measured in seconds of delay per vehicle
 A through F (including E)
 Typically, LOS D or better is acceptable in urban setting
 Queues are measure of vehicular backup (distance)
 Presentation provides comparison of average
intersection LOS and queue
A ≤ 10 A 0 to 10
B > 10 to ≤ 20 B > 10 to ≤ 15
C > 20 to ≤ 35 C > 15 to ≤ 25
D > 35 to ≤ 55 D > 25 to ≤ 35
E > 55 to ≤ 80 E > 35 to ≤ 50
F > 80 F > 50
Source: Exhibit 16-2 and Exhibit 17-2 from
TRB's "Highway Capacity Manual 2000"
Signalized Intersections
Level of
Service
Level of
Service
Control Delay per
Vehicle (sec/veh)
Unsignalized Intersections
Average Control
Delay (sec/veh)
SOURCE: "A Policy on Design of Design of Urban Highways and Arterial
Streets" - AASHTO, 1973 based upon material published in "Highway
Capacity Manual", National Academy of Sciences, 1965.
Visual
Representation of
Level of Service

9. 9
N
Sets Spacing (Distance) Standards Between Intersections
 Reduces conflict points by increasing distance
 Allows more reaction time
 Reduces crashes
 Increases intersection efficiency

10. 10
66 Intersection
Conflict Points
63 Crashes, 2
Fatal Since 2017
50 Sec Avg. Veh
Delay (2019)
No Neighborhood
Sidewalks
Chain Bridge Road – Rte. 123
To Oak
Place
3 Bus Stops in 500’
Increasing Backups
N
Inadequate
Intersection Spacing
Vegetated Buffer
Maintenance
Recommended

11. 11
Chain Bridge Road – Rte. 123
N
Existing (2019) Traffic Operations
 7-Leg Intersection, 6 Signal Phases
 Level of Service: D in both peaks
 Average Delay: 50-55 seconds
Existing (2019) Traffic Volumes
 Chain Bridge Road (Route 123)
◦ 39,000 VPD; 2,200 in peak hour
 Eaton Place
◦ 12,000 VPD; 1,200 in peak hour
 Chain Bridge Service Road (W)
◦ 3,000 VPD; 290 in peak hour
 Chain Bridge Service Road (E)
◦ 4,800 VPD; 480 in peak hour
2040 No-Build Operations
 Level of Service: F
 Average Delay: 91.4 seconds

12. 12
Chain Bridge – Rte. 123
Cobbs
Grove
N
East Service Road
 Existing intersection does not meet City or State
access management requirements for intersection
spacing
 Assembly Drive too close to Rte. 123
◦ Min. 225’ required; 32’ current spacing
 East Service Road(s) too close to Rte. 123
◦ Min. 225’ required, 45’ current spacing
 Safety risk at Eaton/East service roads is reduced
by signalization
 Combination of Assembly Drive access and two-
way traffic along the service road is unsafe
 Any improvement to this National Highway System
(NHS) intersection is required to meet access
management standards
West Service Road

13. 13
Cobbs
Grove
 Existing Intersection Summary
◦ 66 Total conflict points
◦ 49 of 66 are angle conflict points
◦ 6 Conflict points attributed to substandard Assembly
Drive / West Service Road intersection
 3 of 6 are angle conflict points
◦ 22 Conflict points attributed to substandard East
Service Road(s) intersection
 13 of 22 are angle conflict points
 East Service Road(s) intersection at Eaton Place
currently signalized, mitigating conflict risk

14. 14
Looking at reported crash
location “dot” is not adequate,
must consider movement/
direction of each vehicle involved

15. 15
 Existing Crash Type Summary
◦ 63 total crashes October 2017 – October 2022
◦ 37 of 63 crashes (59%) are angle crashes
◦ 10 of 13 injury or fatal crashes (77%) are angle crashes
◦ 49 of 66 conflict points (74%) are angle conflicts
Crashes at Rte. 123 – Eaton Place by Crash Type

16. Red Boxes Indicate Crash
Trends Associated with Traffic
To/From West Side of Rte.
123 ( Assembly / Cobbdale)
16

17. 17
Chain Bridge Road – Rte. 123
Assembly Stop
Location & End
of Sidewalk
Cobbs Grove
Stop Location
Up to 3 Buses Stop at
Each Location In Morning
and Afternoon
Total of 9 Potential Stops
within 500’
Norman
Stop Location
Cobbs
Grove
Ln.
N

18.  Located within VDOT Right of Way
 Features natural berm
 Approx. 0.8 Acres
 Variety of Trees, Shrubs, Vines
18

19.  264 total trees inventoried, 3” & larger*
◦ 105 “Good” condition (40%)
◦ 105 “Fair” condition (40%)
◦ 25 “Poor” condition (9%)
◦ 29 “Dead” condition (11%)
 Primarily deciduous species (not evergreen)
 Southern half of buffer is widest, most effective
◦ Primarily south of Norman Ave
◦ More vegetation and visual buffer than northern half
 Visual buffer enhanced by tangle of vines
◦ Vines may contribute to declining tree health
◦ 39 of 105 “Good” trees, 67 of 105 “Fair” trees have vines
* Tree condition assessment completed by Wetland Studies and
Solutions, Inc., August-September 2022 19

20. 20
 2019
◦ Council Resolution for funding request – Priority 1
 2020 – 2021
◦ City awarded $10.7M NVTA funding
◦ Reevaluate corridor conditions
◦ Concept development
◦ Alternatives analysis
 2022
◦ Continued concept development
◦ Extensive public engagement
◦ Concept adjustments & enhancements

21. 21

22. 22

23. 23

24. 24
Six stakeholder meetings held January – October 2022
Summary of most common requests:
1. Enhance pedestrian and multi-modal facilities
2. Condense and improve school bus stop(s)
3. Eliminate mini-roundabout at Norman Ave
4. Provide dedicated right turn lane at the new signal
5. Keep two-way traffic between Assembly & Norman Ave
6. Complete eastern improvements only, eliminate work
west of Route 123
7. Minimize or eliminate impacts to green buffer between
Route 123 & the Chain Bridge service road
8. Prioritize safety-driven improvements







25. 25
Provide more pedestrian and multi-modal
facility options for neighborhood


26. 26
Condense Bus Stops, Provide Safe
Waiting Area & Sidewalks

Combined Stop
Location
3 Buses Stop at Single
Location In Morning and
Afternoon
Total of 3 Stops

27. 27
Roundabout replaced with traditional 3-
way, stop-controlled intersection

Mini-Roundabout initially proposed to provide
conflict reduction, traffic calming & speed
control, improve off-peak traffic flow
Community feedback, sidewalk connectivity and
additional right turn lane support option for 3-
way stop configuration
Previous Design
Proposed Design

28. 28
Provide a dedicated right turn lane at the new signal
Eastbound Approach Delay from Assembly / Cobbdale
No Build - 104 seconds/vehicle (Existing @ Eaton)
Build – 94 seconds/vehicle to North 123 (10% reduction)
Build - 69 seconds/vehicle to South 123 (34% reduction)


29. 29
N
 One-Way Conversion is Critical to Project-Wide Improvements
◦ Address access management and properly mitigate safety risk
◦ Reduce 7 leg intersection to 4 legs, 4 signal phases
◦ Eliminate 30 conflict points
◦ Reduce 91.4 second/vehicle delay to 38.8 second/vehicle delay
◦ Provide space for sidewalk, path and vegetated buffer strip preservation
◦ Allow opportunity to preserve private landscaping west of service road (boxwoods, etc.)
◦ Address school bus stop safety, supported by FCPS Office of Transportation & Office of Safety & Security

30. 30
N
 One-way traffic configuration on Service Road
 Southbound Chain Bridge Rd dedicated right turn lane
 Neighborhood sidewalk on west side of Service Road
 Shared-use path along Chain Bridge Road
 Existing boxwoods & trees along west side of Service Road

31. 31
 Arborist’s Recommendations for Overall Health & Enhanced Buffer
◦ Forest thinning – primarily targeting dead and poor condition trees
◦ Management program – removal of vines & invasive species
◦ Supplemental planting – evergreen screening plants in thin areas and along path
 Base Scenario – No Shared-Use Path or Right Turn Lane
◦ Eliminate shared-use path & right turn lane to preserve buffer
◦ Remainder of project constructed (i.e. one-way traffic, sidewalk, new signal/intersection)
◦ 94 live trees and 29 dead trees to be removed (of 264 total inventoried)
 Recommended Build Scenario
◦ Includes shared-use path, excludes right turn lane, shifts one-way service road to west
◦ 111 live trees and 29 dead trees to be removed (of 264 total inventoried)
◦ 17 additional trees removal relative to “base scenario” to allow for regional trail facilities along
Rte. 123 corridor to George Snyder Trail, I-66 and beyond, recommend supplemental plantings
Minimize impacts to vegetated buffer


32. 32
N

33.  No-Build
◦ Includes new signal by VDOT
◦ Conflict Points: 66
◦ Delay: 91.4 seconds, Level of Service F (2040)
 Build – Alternate Concept
◦ Provide dedicated signal(s) for Assembly Drive & West Service Road
◦ Eliminate all other improvements west of Rte. 123
◦ Conflict Points: 44
◦ Delay: 75.9 seconds, Level of Service E (2040)
 Build – Recommended Concept
◦ Conflict Points: 36
◦ Delay: 38.8 seconds, Level of Service D (2040)
33

34. 34

35. 35

36. 36
N
3 Southbound Thru-
Lanes, Consistent
from I-66 to Rte. 50
2 Protected
Southbound Left Turn
Lanes to Eaton Place
 Three through lanes provide adequate & consistent capacity from I-66 southbound to Rte. 50
 Protected left turn lane(s) required to address safety issue resulting in two fatalities
◦ Approx. 20% of traffic turning left to Eaton continues to Willow Crescent/North Service Road
◦ Typical single left turn lane can only accommodate approx. 300 lefts in an hour
◦ With new signal, approx. 435 – 505 southbound lefts to Eaton in design year peak hour
◦ Two left turn lanes required to maintain acceptable operations, prevent queue from backing into
southbound through traffic, address intersection safety

37. 37
N
16 Trees Located in
Median to Be Removed
 All trees are in fair to poor condition most with terminal decline
 Terminal decline means the entire tree is progressively deteriorating.
Chain Bridge Road –
Rte. 123
N

38. 38
Conflict
Points
2040
Intersection
Delay
(Sec/Veh)
2040
Intersection
Level
of
Service
2040
Eastbound
Approach
Delay
(Sec/Veh)
Access
Management
Addressed
West
Side
Shared-
Use
Path
Neighborhood
Sidewalk
Bus
Stop
Safety
Buffer
Preserved
Total
Budget
(Millions)
Recommend
No-Build 66 91.4 F 139.4 X X X X  $0.0 X
Recommended Build 36 38.8 D 89.2      $11.4* 
Alternate Build
(Not Recommended)
44 75.9 E 105.1  X X X  $5.0 X
* NVTA funding
available

39. Summary of Primary Benefits
 57% Reduction in Overall Delay
◦ 62% Reduction SB-123
◦ 74% Reduction NB-123
 45% Reduction in Conflict Points
 18% - 75% Reduction in Queue Length
 Enhanced School Bus Stop Safety
 Regional & Local Bike/Ped. Facilities
Summary of Concept
 Removes two east side service road signals
 Converts west side service road to one-way, inbound
 Redirects traffic exiting Cobbdale to new VDOT signal
 Provides protected dual left turn lanes from Rte. 123 39

40. 40
 Improvements primarily constructed within existing right of way
 Limited utility impacts anticipated
 New traffic signal north of Eaton Place constructed by VDOT (I-66)
 City has $10,750,000 in NVTA 70% funding available
◦ Funding subject to rescoring by NVTA for Congestion Reduction Relative to Cost (CRRC)
◦ Anticipated to meet or exceed CRRC rating from original roundabout concept
◦ City may seek additional funds at later date as required
 Estimated Project Budget (Recommended-Build Option)
◦ Engineering & Development: $ 750,000
◦ Right of Way & Utilities: $ 1,200,000
◦ Construction & Oversight: $ 9,450,000*
Total Budget: $11,400,000*
* Includes 30% Construction Contingency & 11% Inflation Factor

41. 41
◦ February 22, 2023: Open house public information session, Sherwood Community Center
◦ March 2023: Seek Council endorsement of recommended design
◦ Spring 2023: Construction of interim safety improvements (SB-123 dual left turn lanes)
◦ Summer 2023: NVTA evaluation of updated concept
◦ Fall 2023: Complete field survey and begin detailed project design
◦ 2024 – 2025: Right of way acquisition and utility relocations
◦ 2025 - 2026: Construct Project

42. 42
 Recommended Design
◦ Shared-Use Path
◦ Sidewalk
◦ Retaining Wall
◦ Buffer Maintained with
Enhanced Landscaping

43. 43
 Recommended Design
◦ Shared-Use Path
◦ Sidewalk
◦ Retaining Wall
◦ Buffer Maintained with
Enhanced Landscaping

44. 44