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

4.
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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?
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6.
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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)

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

10.
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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

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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.
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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.
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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

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

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 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)
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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
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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.
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 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

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23.
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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







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

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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

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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

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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)


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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

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 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.
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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)
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35.
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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

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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

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 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

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◦ 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

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

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

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