NC Local User Group Meeting, July 2016
Designing for Progression and
Smooth Flow
Joe Hummer, Staff Engineer, M&S
Wide Range of Opportunities
• Arterials
• Grade-Separated Intersections
• Interchanges
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Transportation
NC Local User Group Meeting, July 2016
It’s All About Bandwidth:
Kramer-Style Synchronized Streets
Joe Hummer, Staff Engineer, M&S
Kramer’s
Arterial Theory
Kramer’s Arterial
Theory
• Installing a synchronized street at every intersection
along an arterial is difficult
• Instead, only install where needed to maintain perfect
two-way progression
• Steps:
1.
2.
3.
4.
Decide on speed and cycle length
Start at large intersection which is to remain conventional
Compute “half-cycle distance” and plot points
Signals that fall within a few hundred feet of a half-cycle point
can remain conventional; may restrict band slightly or may
need to use lead/lag lefts
5. Signals not near a half-cycle point must be converted to
synch. street
6. Can repeat with different speed, cycle length, and/or starting
point to find better solution
Transportation
Example: Gardiner Boulevard,
ExampleDowntown Toronto
Proposed 8-lane divided street, 3000+ vph WB,
1500+ vph EB, heavy pedestrian crossing demand
Conventional v/c
0.96
0.91
1.00
1600’
0.64
1300’
1400’
1000’
0.59
Demands, vph
EB left
480
120
60
WB left
120
60
110
NB left & th
210
310
140
SB left & th
70
90
100
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Transportation
No Progression Eastbound
120-sec cycle, 30 mph progression speed
Time,
sec
90
60
30
0
0
800
1600
2400
3200
4000
4800
Distance, ft
6
Transportation
Proposed
Solution
Proposed
Solution
Synch street at second and fourth intersections, others remain conventional
Proposed v/c
0.96
0.91
0.78
1600’
1000’
0.54
1400’
0.59
1300’
Crossovers
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Transportation
Good Progression Both Directions
Same cycle and progression speed
Time,
sec
90
60
30
0
0
800
1600
2400
3200
4000
4800
Distance, ft
8
Transportation
NC Local User Group Meeting, July 2016
Lane Continuity
Problems and Opportunities
Joe Hummer, Staff Engineer, M&S
Definition
• “Drivers should not have to change lanes to follow a certain main
interstate route.”
• “Helps meet driver expectations, avoid driver confusion, and ultimately
eliminate collisions.”
• Handbook of Transportation Engineering, 2nd ed., 2011
• Applies to other routes as well, although perhaps not with same intensity
as interstates
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Transportation
Related Concepts
• Route continuity is a subset of lane continuity
• Main route is through route at interchange regardless of orientation
• Also related to basic number of lanes and lane balance
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Transportation
Guidance
• AASHTO Green Book does not mention “lane
continuity,” but
• “Consistency should be maintained in the number of
lanes provided along any route of arterial character.”
(p. 10-72)
• ITE Traffic Engineering Handbook, p. 297: “The
principles of route continuity, lane continuity, lane
balance, and maintaining the basic number of lanes
must be considered collectively.”
• Geometric Design Guide for Canadian Roads, 1999,
page 2.1.7.1
• Definition
• Several paragraphs
• Several examples
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Transportation
Examples
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Transportation
Crashes
• Lane changes lead to sideswipe crashes
• Lane change crashes are about 4% of total (200,00/yr in US)
• 10% of all crash-caused delay
• Over 50% of lane change crashes on roads with speed limit of 45
mph or lower
• 26% of lane change crashes attributed to driver distraction in 2002
• Higher now?
• Providing lane continuity at a freeway diverge reduces crashes
• By 68% at one-lane ramp
• By 32% at two-lane ramp
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Transportation
Delay--Guess Where the Lane Discontinuity Is on I-540
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Transportation
Extent of Problem in NC
• Based on request in early June to RTEs, circulated to some DTEs and
design engineers
Thank You!
• 30 verified cases submitted
• Asheville to Wilmington
• Urban and suburban roadways
• By route:
•
•
•
•
•
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12 interstate
5 US
1 US Alternate
3 NC
9 secondary
Transportation
Types of Discontinuities
• 11 add right then drop left
• 7 add left then drop right
• 3 drop right then add left
• 2 drop left then add right
• 1 drop right then add right
• 5 left lane drop
• 1 multiple
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Transportation
Distances
• 24 cases of add then drop or
drop then add
• Average distance = 1.86
miles
• Range 0 to 12 miles
• Shortest forced lane change
is 0.08 miles (400 feet)
• 14 cases with distance under
2/3 mile
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Transportation
Number of Lanes
• 10 with 1 through
lane
• Mostly SR
cases, but one
interstate
• 17 with 2 through
lanes
• 2 with 3 through
lanes
• 1 with 4 through
lanes
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Transportation
How Did They Happen?
• 9 TIP projects
• 3 fixed before opening
• 2 fixed shortly after
opening
• 4 not yet fixed
• 6 development
• 5 new route numbering
• 4 widening expected
someday
• 3 City involvement
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Transportation
What Can We Do
• Stay vigilant
• DOT projects
• City projects
• Developers
• Don’t assume
next project will
get done
• Be skeptical of
the forecast
• Watch work
zones
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Transportation
What Can We Do to Fix Existing Sites
• 25 sites not yet fixed
• 10 could be restriped with few
apparent issues
• 7 could be restriped but there
would be negative impacts
• 4 lose capacity
• 2 make entering more
difficult
• 1 narrower lanes
• 3 upcoming TIP project
• 3 need widening
• 2 no apparent solution
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Transportation
My Action Items
• Develop policy
• Write paper
• Make more presentations
• Sponsor research on developing a model to
predict crashes due to lane changes
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Transportation
NC Local User Group Meeting, July 2016
Grade Separated Intersections
Joe Hummer, Staff Engineer, M&S
Definition
• Intersections with at least one bridge
• Neither intersecting route is a freeway
• Both streets can have signals
• Higher cost than at-grade
• Higher capacity that at-grade
• Is it fair to compare to at-grade?
• How is funding usually allocated?
Transportation
What is Wrong with This Design in This Spot?
Dawson/McDowell at Western/ML King
Transportation
What is Wrong with This Design in This Spot?
Dawson/McDowell at Western/ML King
High speed
Peds
No metering
Progression
Too much ROW
Transportation
Unique Designs
Single Quadrant, Jackson, OH
Transportation
New Designs
Echelon Interchange
Transportation
New Designs
Center Turn Overpass
Arterial or collector
Arterial
Transportation
Two-Level Signalized
• Invented in Korea
by Lee
http://www.intersec
tionsystem.com/e
ng/product01.html
• Patented in US
and elsewhere
• None built so far
• Published several
times
Transportation
Single-Point and Superstreet
From Dennis Eyler, SRF Consulting, Minneapolis, MN, 2011
Transportation
Contraflow Left Intersection
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Scoring the Designs
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Design
Progression
(of 5)
Good aspects
Poor aspects
Total score
(of 60)
Diamond
0
Distance traveled,
unusual maneuvers
Capacity, peds
32
Parclo A
1
Capacity, conflict points
Distance traveled,
peds
31
Cloverleaf
5
Capacity,
wrong way potential
Distance traveled,
cost, peds
23
Single
quadrant
3
Metering, cost, peds
Efficiency,
unusual maneuvers
40
Echelon
5
Everything except…
Bridge cost, peds
47
Center turn
4
Everything except…
Bridge cost
46
Two level
5
Everything except…
Bridge cost
49
Half-half
5
Everything
Nothing
49
Contraflow
5
Everything
Nothing
49
Transportation
Recommendations
• Recognize that grade separated intersections
are not interchanges
• Use an appropriate design
• Analyze all contenders
• Consider all users
• Someone needs to investigate patent situation
of echelon and two-level
Transportation
NC Local User Group Meeting, July 2016
Use Better Parclo B’s Instead of
Awful Parclo A’s
Joe Hummer, Staff Engineer, M&S
Why Build an Awful Parclo A
When You Can Build a Better Parclo B?
Parclo A
37
Parclo B
Transportation
Why Parclo B is Better
38
Aspect
Parclo A
Parclo B
Progression
Two full signals at 1200foot spacing = no chance
for two-way progression
All signals only affect one
direction = perfect twoway progression
Lane utilization
All turning traffic
stacked in right lane
Left turn traffic in left
lane, right turn traffic in
right lane
Unusual
maneuvers
Left turn traffic
has to turn right
Left turn traffic stays left,
right turn traffic stays
right
Pedestrians
Each pedestrian must cross
two free-flowing ramps
All ramp crossings are
signal-controlled
Transportation
In All Other Important Respects
Parclo A and Parclo B are Equal
• Capacity
• Distance traveled
• Conflict points
• Wrong way potential
• Bridge size
• Right of way
• Extent along freeway
• Extent along arterial
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Parclo B !
Transportation
Recommendations
• Build parclo B’s instead
of parclo A’s
• Convert parclo A’s into
parclo B’s
• Convert parclo A’s into
parclo AB’s
• Convert parclo A’s into
something better
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Transportation