Post on 06-Jan-2018
description
MULTIMODAL ACCESSBILITY
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1 PHYSICS OF CITIES – SCIENCE OF ACCESSIBILITY
2 A NEW ACCESSIBILITY FRAMEWORK
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PRESENTATION OVERVIEW
ACCESSIBILITY APPLICATIONS
1 THE PHYSICS OF CITIES
Yes Virginia, there is a science behind this
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In the natural world, gravity warps the space-time continuum Gravity compresses (slows) time
In cities, density (urban gravity) warps the distance-time continuum
Time stays constant and limited Distance between places varies
Density compresses distance Speed decompresses distance
THE PHYSICS OF CITIES
ACCESSIBILITY SCIENCE
High gravityCompressed space-time
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Number of needed and preferred opportunities (city design elements) within a reasonable amount of time (design target)
Travel to work Long commutes impact quality of life
Commute time to work averages around 20 to 25 minutes Long commutes impact economic development
Employers locate where needed employees are within reasonable commute times
Non-work travel Nearby retail and services impact neighborhood quality
Wegmens, food desert phenomena Retailers live and die by accessibility to roof-tops
I.e., groceries require around 3,000 rooftops within 10 minutes
ACCESSIBILITY MEASURES DENSITY (URBAN GRAVITY)
ACCESSIBILITY SCIENCE
“I was dealing with at least two hours a day of stress.”
Two weeks ago, Greene took a new job about 10 minutes from home.
“It’s liberating,” she says. “I can make dinner plans. I am so much happier.”Miami Herald, May 5, 2015
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Where:
OPPORTUNITIES = Number of Jobs (HBW) or Number of Retail/Service Establishments (HBNW)
TRAVEL TIME = Time to reach opportunity over actual network (Network Analyst)
DECAY* = Factor reflecting decrease in value of opportunities that are farther away
MEASURING ACCESSIBILITY
ACCESSIBILITY SCIENCE
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ACCESSIBILITY – REASONABLE TIME (TIME DECAY)
ACCESSIBILITY SCIENCE
Opportunities further away have less value
The value, or decay, is consistent and strong (results from WashCOG travel survey)
Decay varies by: Trip purpose Travel mode
DECAY CURVES
0 10 20 30 40 50 60 700
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20
30
40
50
60
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80
90
100
f(x) = 100 exp( − 0.0701381566112441 x )R² = 0.981330531243287
Travel Time Decay – Walking for Work Trips
Minutes
Perc
ent o
f Trip
s whi
ch a
re L
onge
r Tha
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Trips requiring 15 min-utes have only 37% of the value of trips < I minute
0 10 20 30 40 50 60 700
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20
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90
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f(x) = 100 exp( − 0.0968935999994943 x )R² = 0.994208715309704
Travel Time Decay -- Walking for Non-Work
Minutes
Perc
ent o
f Trip
s Whi
ch A
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r Tha
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Trips requiring 15 min-utes have only 23% of the value of trips < I minute
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ACCESSIBILITY – TRAVEL TIME & DISTANCE AND SPEED
Average Commute
Distance (mi) Speed (mph)1 32 63 94 125 156 187 218 249 27
10 3011 3312 3613 3914 4215 4516 4817 5118 5419 5720 60
Reasonable commute time = 20 minutes
A destination one mile away requires an average speed of 3 mile per hour
A destination 10 miles away requires 30 mph
A destination 20 miles away requires 60 mph
TIME TARGET
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
10
20
30
40
50
60
70
Distance
Spee
d
ACCESSIBILITY SCIENCE
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
20000
40000
60000
80000
100000
120000
140000
160000
180000
CBDFringe
Distance
Acce
ssib
ility
Sco
reACCESSIBILITY – NEEDED AND PREFERRED OPPORTUNITIES
Assume average accessibility target of 10,000
CBD location meets target in 1 mile
Fringe location meets target in 12 miles
Speed is needed to overcome low densities
ACCESSIBILITY TARGET
High density
Low density10,000 score
ACCESSIBILITY SCIENCE
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ACCESSIBILITY DESIGN STRATEGIES
ACCESSIBILITY SCIENCE
Strategies to meet travel time target
Both examples assume 25 minute travel time target
Mobility example requires 31 mph speed to cover 13 miles
Proximity example requires 20 mph to cover 8 miles
MOBILITY vs PROXIMITY
Mobility model(lower densities, higher speeds)
Facility Rate (mph) Time (min) Distance (mi)Local 15 2 0.5Collector 20 1.5 0.5Arterial 25 14.4 6Expway 50 7.2 6
31 25.1 13
Local CollectorArterial
Expressway
Home
Work
Same times but different speeds and distances
Facility Rate (mph) Time (min) Distance (mi.)Local 15 1.2 0.3Collector 20 24 8Arterial 25 0 0Expway 50 0 0
20 25.2 8.3
Proximity model (higher densities, lower speeds)
Home
Work
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ACCESSIBILITY DESIGN STRATEGIES
ACCESSIBILITY SCIENCE
Walk the slowest mode, hence requiring the highest density
Auto the fastest mode, hence providing density trade-off
Auto speed heavily influenced by network design (later)
ALTERNATIVE TRAVEL MODES
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DISTANCE, SPEED AND MODE
Average Commute
Distance (mi) Speed (mph)1 32 63 94 125 156 187 218 249 27
10 3011 3312 3613 3914 4215 4516 4817 5118 5419 5720 60
Reasonable commute time = 20 minutes
Walk speed requires opportunities within 1 mile
Bike speed 5 miles Transit speed 8 miles Auto speed 14 miles+
DISTANCE AND SPEED IMPACT MODE
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
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20
30
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50
60
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Distance
Spee
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çWalk
Bike
Premium transit
Auto
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çWalk
Bike
Premium transit
Auto
ACCESSIBILITY, SPEED AND MODE
ACCESSIBILITY SCIENCE
CBD has enough opportunities to make walking viable
Walk, bike and transit modes don’t provide enough speed to reach target opportunities from fringe location
TRAVEL MODE VIABILITY
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
20000
40000
60000
80000
100000
120000
140000
160000
180000
CBDFringe
Distance
Acce
ssib
ility
Sco
re
10,000 score
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THE SCIENCE PLAYS OUT EVEN IN TODAY’S AUTO ORIENTED WORLD
ACCESSIBILITY SCIENCE
Very few in Manhattan own a car
Yet incomes are among the highest in the country
Density provides enough access to make walking viable
Cars take up space, reducing density
HOUSEHOLDS WITHOUT A CAR
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A NEW FRAMEWORK
Expanding the focus beyond transportation facility levels of service
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CITY DESIGN FOCUSES ON SPEED
ACCESSIBILITY FRAMEWORK
• Roadway level of service measures the impact of congestion on speed
• Key assumption is: as speed drops, so does accessibility
• Given the influence of density, is that always true?
ROADWAY LEVEL OF SERVICE (LOS)
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DESIGNING FOR SPEED
Red indicates severe congestion
Lightest green indicates moderate to no congestion
Most roads congested, focusing attention on added capacity
Focus drains limited funding
But will those improvements really help?
ROADWAY LEVEL OF SERVICE
• Most congestion along I-270 and I-95 corridors
• Heavy congestion on and around the beltway
ACCESSIBILITY FRAMEWORK
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DESIGNING FOR ACCESS
Auto accessibility is baseline for establishing levels of service
Average weighted access score is LOS C
LOS A and B is better than average
LOS D, E and F worse than average
UNCONGESTED ACCESSIBILITY
• Access rings around DC urban gravity (density)
• Speed provides access along I-270 and I-95
• Lower order magnitude gravity rings around Frederick
A
B
C
DE
ACCESSIBILITY FRAMEWORK
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DESIGNING FOR SPEED
Accessibility scores rerun with congested versus uncongested speeds
Results indicate biggest impacts away from urban gravity (density)
CONGESTED ACCESSIBILITY
• LOS A ring near DC doesn’t change much except along I-270 and I-95
• LOS B area pulls in dramatically around DC (reflecting the weight of density over speed)
• Frederick drops from D to E (economic impacts?)
A
B
C
DE
ACCESSIBILITY FRAMEWORK
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DESIGNING FOR SPEED
Focus on roadways suggests area along beltway is highly congested, yet accessibility remains A
Without accessibility context, agencies focus on fixing congested roads, regardless of location
Focus leads to wrong projects and funding priorities
ACCESSIBILITY VS ROADWAY LOS
• Roadway congestion highest in A accessibility area
• Congestion along I-270 and I-95 causing drop along those corridors
A
B
C
DE
ACCESSIBILITY FRAMEWORK
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DESIGNING FOR SPEED
Transit accessibility LOS on same scale as auto LOS accessibility
Improving transit LOS a heavy funding lift
Most of corridor has extremely poor transit accessibility
Several locations close to DC and along Metro rail have LOS A
TRANSIT ACCESSIBILITY
• Transit access LOS A only in areas with premium transit and transit oriented development
• Areas with LOS A also have non-auto mode shares greater than 50%
A
B
C
DE
ACCESSIBILITY FRAMEWORK
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APPLYING ACCESSIBILITY
What we’ve learned so far
SHIRLINGTON WALK DEMAND – NCHRP 770 APPLICATION
ACCESSIBILITY APPLICATIONS
New link results in 500 new walk trips
ASHEVILLE ACCESSIBILITY FOR LOW INCOME NEIGHBORHOODS
ACCESSIBILITY APPLICATIONS
Problem: limited access to food stores for southern portion of study area
Best solution: provide new food market! Existing markets too far for walking
DC ACCESSBILITY BASED LOCATIONS FOR LOW INCOME HOUSING
ACCESSIBILITY APPLICATIONS
MDOT MODE SHARE ESTIMATION
ACCESSIBILITY APPLICATIONS
77.7%
6.9%
11.1%
4.2%
67.8%
5.4%
12.1%
6.8%
73.8%
6.9%
8.7%
5.0%
45.9%
2.1%
35.6%
10.7%
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WASHCOG GHG MODELING
ACCESSIBILITY APPLICATIONS
MULTIMODAL ACCESSBILITY
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Interplay between travel time and cost
Accessibility has valueMore access, creates more opportunities
Access trade off with land values and rentsSteady drop from metro center (concentric ring theory)
Metro equilibrium curveSome value time, others value space“Drive till you qualify”
High speed, high capacity transportation modifies access contoursRadial corridors stretch access from metro center (sector theory)Circumferential corridors (belt routes) intersecting with radial routes create high access centers (edge cities) (multiple nuclei theory)
Modified access contours create consistent metropolitan patternsCircus tent (central place theory)
ACCESSIBILITY SHAPES METRO AREAS
ACCESSIBILITY PLANNING
Show Houston / Beijing patterns or Washington circus tent
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As an element changes, others respond
Accessibility has valueMore access, creates more opportunities
Access trade off with land values and rentsSteady drop from metro center (concentric ring theory)
Metro equilibrium curveSom“Drive till you qualify”
High speed, high capacity transportation modifies access contoursRadial corridors stretch access from metro center (sector theory)Circumferential corridors (belt routes) intersecting with radial routes create high access centers (edge cities) (multiple nuclei theory)
Modified access contours create consistent metropolitan patternsCircus tent (central place theory)
METRO AREAS SEEK EQUILIBRIUM
ACCESSIBILITY PLANNING
Show patters
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Access to an opportunity is the product of mobility (travel speed) and proximity (land use)
ACCESSIBILITY INTEGRATES TRANSPORTATION AND LAND USE
MOBILITY(NETWORK)
PROXIMITY(LAND USE)
ACCESSIBILITY(OPPORTUNITY)
&
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ACCESSIBILITY IS INFLUENCED BY TRANSPORTATION AND LAND USE
• Closer destinations allow slower speeds to attain reasonable travel time
• At slower speeds (around 25 mph), all of the network is in play
• Further destinations require higher speeds,
• At higher speeds (over 35 mph) only high speed facilities are in play
Mobility and proximity are accessibility strategies
Mobility model(lower densities, higher speeds)
Facility Rate (mph) Time (min) Distance (mi)Local 15 2 0.5Collector 20 1.5 0.5Arterial 25 14.4 6Expway 50 7.2 6
31 25.1 13
Local CollectorArterial
Expressway
Home
Work
Same times but different speeds and distances
Facility Rate (mph) Time (min) Distance (mi.)Local 15 1.2 0.3Collector 20 24 8Arterial 25 0 0Expway 50 0 0
20 25.2 8.3
Proximity model (higher densities, lower speeds)
Home
Work