Suburban Sprawl, Road Building and Vehicle Emissions

Image via WikipediaLock-in Effects of Road Expansion on CO2 Emissions: Results from a Core-Periphery Model of Beijing ( 39 page pdf, Alex Anas and Govinda R. Timilsina, Working Papers, State University of New York at Buffalo, Jun. 9, 2010)

By applying a traffic speed model to the megacity of Beijing, today’s review article examines the relationship between the addition of urban roads to traffic speed and emissions of CO2 and to what extent public transit plays an offset role for these emissions.



Key Quotes:

“Adding urban roads alleviates congestion, speeds up traffic and lowers CO2 in the intensive

margin (per car-km). But faster traffic attracts more car-trips in the extensive margin”

“The combined effect often increases aggregate emitted CO2. How much can improving public transit offset the higher emissions caused by new roads?”

“effective antidotes to substantial road expansion in the periphery of megacities:

1. to make improvements in transit service in the periphery - drawing peripheral trips away from the car and onto transit.
2. to reduce the core’s road capacity - increasing congestion per km in the core and thus inducing trips to switch to other modes, and to the less congested periphery”

“main drivers for the lock-in condition as it applies to developing megacities:

1. Road capacity works powerfully in the extensive margin, overcoming the beneficial effects of the same capacity expansion in the intensive margin
2. The relatively low market share of car trips and the large market share of the non-motorized modes that are observed in the megacities is part of the reason for the low cross-elasticity of car choice with respect to transit travel time relative to the own elasticity of car choice with respect to the travel time by car
3. The presence of a large number of non-motorized travelers switching to bus dilutes the beneficial effects of car trips switching to transit

“Reducing roads in the core or making faster transit in the periphery draws population to the less congested periphery. While such a shift adds to urban sprawl, aggregate emissions are lowered and there is relatively less lock-in from adding peripheral road capacity”

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