multimodal accessbility. 1 2 3 1 physics of cities – science of accessibility 2 2 a new...

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)


“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


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ACCESSIBILITY – REASONABLE TIME (TIME DECAY)


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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f(x) = 100 exp( − 0.0701381566112441 x )R² = 0.981330531243287

Travel Time Decay – Walking for Work Trips

Minutes

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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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f(x) = 100 exp( − 0.0968935999994943 x )R² = 0.994208715309704

Travel Time Decay -- Walking for Non-Work

Minutes

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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

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Distance

Spee

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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

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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


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ACCESSIBILITY DESIGN STRATEGIES


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


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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Distance

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çWalk

Bike

Premium transit

Auto

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çWalk

Bike

Premium transit

Auto

ACCESSIBILITY, SPEED AND MODE


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

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CBDFringe

Distance

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10,000 score

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THE SCIENCE PLAYS OUT EVEN IN TODAY’S AUTO ORIENTED WORLD


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


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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


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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


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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


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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%

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B

C

DE


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APPLYING ACCESSIBILITY

What we’ve learned so far

SHIRLINGTON WALK DEMAND – NCHRP 770 APPLICATION


New link results in 500 new walk trips

ASHEVILLE ACCESSIBILITY FOR LOW INCOME NEIGHBORHOODS


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


MDOT MODE SHARE ESTIMATION


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


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

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