Riordan Frost, PhD Candidate
Department of Public Administration & Policy, American University
The role of state smart growth policies in transportation
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What affects how we get around?
•The cost of each mode: driving alone decreases when fuel costs rise, and sustainable modes all decrease
when fuel costs fall (Ferguson 1997; DeLoach & Tiemann 2012)
•Income: low-income commuters carpool and take public transportation more, due to the lower user cost
(Ferguson 1997; Glaeser et al. 2008)
•Environmentalism: environmental views and sustainable mode choices are positively correlated on the
community-level (Kahn & Morris 2009)
What is the role of state smart growth policies?
•State policies succeed in the areas states prioritize (Ingram et al. 2009)
•Maryland prioritizes environmental protection, Oregon prioritizes transportation, New Jersey
prioritizes affordable housing
•The Oregon planning law establishing the Portland urban growth boundary was not found to affect rates
of driving alone (Jun 2008)
•States with growth management policies appear to experience lower density declines (Anthony 2004)
Do state smart growth policies positively affect sustainable transportation rates?
Sustainable transportation: public transit, carpooling, bicycling, and walking
•Using difference-in-differences analysis to compare sustainable transportation rates in Colorado and
Maryland before and several years after the 2009 and 2010 Maryland smart growth policies
•This method compensates for non-random treatment and attempts to determine causal effects
•To ensure there is no bias from pre-existing trends, event study analysis is conducted (see Fig. 4)
•Two approaches: differencing and logistic regression
•(Sustainable transportation)it = ƛ(β0 + β1(sg)ij + β2(year)jt + β3(yearjt*sgij) + β4(education)ijt + β5(ln(income)ijt)
+ β6(gender)ijt + β7(race)ijt + β8(rent/own)ijt)
•Driving alone is the most widely used, but least efficient mode of personal transportation
•Driving contributes to congestion, local air pollution, and infrastructure burden — and
greenhouse gas emissions (see Fig. 1 & 2)
•‘Alternative’ modes are encouraged by government and business programs for their societal
benefits and company benefits (e.g. less parking demand)
•Here, these modes — public transit, walking, bicycling, and carpooling — are combined
into a new variable: ‘sustainable transportation’
•There are only 11 states with comprehensive smart growth policies
What is smart growth?
•“Building urban, suburban and rural communities with
housing and transportation choices near jobs, shops and
schools” (Smart Growth America 2015)
•A bundle of principles including mixing land uses, creating a
range of housing opportunities, providing a variety of
transportation choices, and preserving open space (EPA 2014)
•Finding: there is approximately a 2 percentage point difference between the sustainable transportation rates in
Baltimore and Denver, attributable to the state smart growth policies of Maryland
•A two percentage point difference is a 10% increase in current sustainable transportation rates
•This change results in substantial GHG mitigation (see Fig. 1 & 2)
•Limitations: more than one policy passed in Maryland; no uniform policy across states for comparison; !
no non-commuting data available
•Next steps: look at other metropolitan areas; examine other smart growth goals (e.g. mixed uses, affordable
housing, and open space); use synthetic controls instead of difference-in-differences
Figure 4: Event study analysis
Baltimore MSA Denver MSA
Figure 2: Cars and light-duty trucks’ share of
transportation GHGs in 2011 (Source: EPA 2013)
Passenger Cars &
Ships & Boats
Figure 1: Transportation’s share of US GHGs
in 2011 (Source: EPA 2013)
Figure 3: 2013 commuting by mode in the US (excluding work-at-home and misc.)
(Source: US Census Bureau 2014; own work)
How do we get to work?
Table 2: Difference-in-differences
•American Community Survey data from the Integrated Public Use Microdata Series (IPUMS-USA)
•Denver and Baltimore metropolitan areas chosen due to similar demographics and the fact that
Maryland has state smart growth policies and Colorado does not
•Metropolitan areas chosen to include the transportation behaviors of urban and suburban residents
•Pooled cross-sectional sample: N = 47,000
Median HH Income (2012)
% College Educated (2012)
Table 1: Similarities between Baltimore and Denver MSAs (Source: Census Bureau 2013)
Table 3: Logistic regression DD - average partial effects
*** p<0.01, ** p<0.05, * p<0.1
Year * smart growth
Education (ref: college)
Gender (ref: female)
Race (ref: white)
Rent/own (ref: renter)