Does rationing really backfire? A critical review of the literature on license-plate-based driving restrictions

Figures & data

Table 1. Summary findings of 40 papers examining the results of license-plate-based driving restrictions.

Publication	Location	Main research approach	Main findings
Studies finding license-plate-based restrictions reduced pollution or congestion
Viard and Fu (2015)	Beijing	Before and after (odd-even and one day per week) examination of daily air quality index and hourly television viewership (regression discontinuity design)	Reduced pollution and increased television viewership (assumption related to less time spent commuting)
Liu, Yan, and Dong (2016)	Beijing	Before and after (odd-even and one day per week) examination of daily air quality index and hospitalisations (regression discontinuity design)	Reduced pollution and hospital admissions
Lu (2016)	Beijing	Before and after examination of reducing policy hours and later increasing penalty for violations on air quality index (regression discontinuity design)	Strengthening the policy associated with improved air quality. Weakening the policy associated with reduced air quality
Gu et al. (2017)	Beijing	Compares household behaviour on restricted days to household behaviour on unrestricted days using travel diaries	Decreased car trips on restricted days
Liu, Huang, Guo, and Guo (2017)	Beijing	Compares daily hospital admission for respiratory issues on high-restriction and low-restriction days using #4 "death" plate (roughly 14% instead of 21% banned)	Reduced hospital admissions on days with more cars banned
Zhang et al. (2017)	Beijing	Examine unique subway card data to identify users that only use the subway on one consistent day per week, assume these switched from driving due to policy, and estimate pollution reduction from removing trip	A small shift in trips from private cars to metro (0.12%) with a corresponding decrease in CO2 emissions
Zhong et al. (2017)	Beijing	Compares daily/hourly air quality index, traffic congestion index, and daily ambulance call data using “death” plate to compare high- and low-restriction days	Lower pollution, congestion, and hospital admissions on days with more vehicles banned
Yang et al. (2018)	Beijing	Compares daily public transit use, taxi use, and congestion using “death” plate to compare high and low restriction days	Reduced congestion and increased taxi and transit use on days with more restricted vehicles
Chen, Qin, et al. (2020)	Beijing	Examines shift in traffic congestion index using “death” plate design by geography and compares to shifts in travel speeds	Finds that traffic congestion index increases by 0.5–0.7 on days with fewer cars restricted
Liu and Kong (2021)	Beijing	Compares differences in changes in air pollution index on weekdays and weekends in Beijing relative to Tianjin using a differences-in-differences approach	Finds a 3%-to-5% reduction in pollution from the license-plate policy with another 8%-to-12% reduction attributable to other policies.
Rajabov et al. (2020)	Beijing	Compares multiple particulates using “death” plate to compare high- and low-restriction days	Finds reductions in AQI, PM2.5, PM10, CO, and NO2, but no difference in O3
Yang et al. (2020)	Beijing	Examines shift in vehicle density using “death” plate design by geography and compares to shifts in travel speeds	Statistically significant increase in vehicle density and decrease in travel speeds on days when fewer cars are restricted. Effects most pronounced in central locations
Zhang, Chen, et al. (2020)	Beijing	Compares household mode choice at restricted and unrestricted hours on weekdays and weekends using travel diaries	Residents travelling at restricted hours less likely to use a car relative to differences between the same time periods on unrestricted weekends
Zhang, Shan, Wang, Pang, and Guo (2020)	Beijing, Tianjin	Before and after examination of daily air quality index (regression discontinuity design)	Modest air quality improvement in both cities
Rao et al. (2017)	Delhi	Intercept survey asking respondents about effects of restriction on current and recalled travel behaviour	Increased speeds, shorter travel times, and shift from cars to transit
Mishra et al. (2019)	Delhi	Compares PM1.0 and PM2.5 on six days during temporary odd-even restriction to three days in weeks preceding restriction on three major arterials	Particulate matter decreased by an average of 5% on arterials during restricted hours
Han, Liu, and Lu (2020)	Jinan	Compares daily CO, PM10, and mortality rates before and after temporary restrictions	Reduction in CO (46.6%), PM10 (33.1%), and morality (0.313 per million people per percent of PM10)
Liu et al. (2018)	Langfang	Before and after (every other day vs. one day per week) comparison of non-compliance, travel speed, and traffic volumes by space and time of day (regression discontinuity design)	Traffic speeds increased with more frequent restriction
Carrillo et al. (2016)	Quito	Before and after examination of hourly CO in restricted zones and times relative to unrestricted times and zones	Improved air quality at restricted times and locations
Barahona et al. (2020)	Santiago	Compares the share of high-polluting vehicles in the fleet in Santiago relative to other municipalities over time (regression discontinuity design)	Santiago has significantly fewer older cars without catalytic converters and these emit less pollution on average
Studies with negative or null findings
Wang et al. (2014)	Beijing	Compares residents’ mode choice on days when household vehicle is restricted using travel diaries	No significant change in probability of travelling by car instead of transit, bike, or foot
Xiao, Chang, Guo, Chen, and Tian (2019)	Beijing	Before and after examination of daily air quality	No evidence of improved air quality
Bonilla (2019)	Bogota	Before and after examination of two phases (peak hours only and 6am-8pm restrictions) on hourly CO (regression discontinuity design)	No evidence of improved air quality
Chen, Zheng, et al. (2020)	Chinese cities (11)	Before and after comparison of annual PM10 and car registrations in eleven cities with restrictions compared to 100 without restrictions	Air quality worsened and car registrations increased in cities with restrictions
Ye (2017)	Lanzhou	Before and after examination of hourly air quality index (regression discontinuity design)	No evidence of improved air quality. Some evidence of worsened air quality
Eskeland and Feyzioglu (1997)	Mexico City	Before and after comparison of quarterly gasoline consumption	Increased gasoline consumption
Davis (2008)	Mexico City	Before and after examination of hourly, daily, and weekly air quality (regression discontinuity design)	No evidence of improved air quality. Some evidence of worsened air quality
Davis (2017)	Mexico City	Before and after examination of policy change to include Saturday restrictions on air quality (regression discontinuity design)	No evidence of improved air quality
Guerra and Millard-Ball (2017)	Mexico City	Compares the daily vehicle travel of households with a single banned car to that of similar households with a single car that is likely exempt because of vehicle age using travel diaries	No evidence of reduced driving from households with a banned car
Studies with mixed findings
Sun et al. (2014)	Beijing	Compares peak travel speeds and daily PM10 using “death” plate to compare high and low restriction days	Traffic speeds increased on days with more restricted vehicles, but no air quality improvement
Ma and He (2016)	Beijing	Before and after examination of hourly air quality index	Air quality improved in short run but worsened in the long run
Xie et al. (2017)	Beijing	Before and after examination of daily air quality index	Air quality improved in short run but not in the long run
Zhang et al. (2017)	Bogota	Before and after examination of hourly air quality measures (regression discontinuity design)	Decrease in NO but increases in NO2, NOx, and O3
Chen, Zhang, and Chen (2021)	Chinese cities (15)	Compares change in PM2.5 over time relative to 158 control cities using a differences-in-differences approach with propensity score matching	No evidence of reduced pollution across the full sample but variation in results across regions and city types with an 11% reduction in air pollution outside of provincial capitals
Chowdhury et al. (2017)	Delhi	Compares satellite-based PM2.5 estimates during a 15-day odd-even restriction to time periods immediately before and after the restriction	Reduces PM2.5 by 4–6%, which is within the 10% uncertainty range of the satellite-based estimates and therefore a null finding
Mohan et al. (2017)	Delhi	Compares PM2.5, traffic speeds, and congestion measures immediately before, during and after implementation of two-week odd-even scheme	Car volumes decrease by 7–19% but there is an increase in exempt auto rickshaws, two-wheelers, and buses. Speeds up around 5% on average and no measurable change in pollution
Joshi et al. (2016)	Delhi	Compares PM2.5 measures immediately before and after implementation of odd-even scheme	Pollution decreased immediately after policy implementation with a subsequent increase, likely due to forest fires
Huang et al. (2017)	Lanzhou	Before and after examination of hourly air quality measures (regression discontinuity design)	Air quality improved in short run but not in the long run
Gallego et al. (2013)	Mexico City	Before and after examination of daily air quality measures (regression discontinuity design)	Air quality improved in short run but worsened within a year
de Grange and Troncoso (2011)	Santiago	Before and after examination of long-term policy and short-term emergency measures on hourly vehicle flows and daily transit ridership	Long-term policy of excluding cars with catalytic converters not associated with reduction in driving. Short-term emergency measures extending the ban to all vehicles associated with reduced driving and increased metro use

Figure 1. License-plate-based restrictions’ relationships to vehicle purchase decisions, travel behaviour, congestion, and pollution.

Figure A1. Cumulative total number of peer-reviewed publications referencing the second-car hypothesis and seminal papers from 1995 to 2020.

Figure A2. Geographical distribution of papers referencing the second-car hypothesis by focus on license-plate-based restrictions. Papers with multiple study cities are counted multiple times.

Table A1. Regression discontinuity estimates of the relationship between Hoy No Circula and annual vehicle registrations (natural log) using a fifth-order polynomial time trend.

	Parameter estimates		Standard errors
Geography	Davis (2008)	Re-Estimate	Unadjusted	Newey West^a	Bootstrapped^b
Mexico City	0.189	0.198	0.097.	0.094*	0.147
Mexico State	NA	0.220	0.225	0.233	0.986
Aguascalientes	NA	0.186	0.063**	0.050**	0.186
Puebla	NA	0.160	0.105	0.081.	0.160
Queretaro	NA	0.166	0.088.	0.078.	0.146
Country	NA	0.164	0.035***	0.076*	0.131

Notes: Significance codes “***” 0.001 “**” 0.01 “*” 0.05 “.” 0.1; ^aNewey West standard errors apply one-year lag. ^bBootstrapped standard errors estimated over 50,000 iterations.

Figure A3. Regression discontinuity plots of the relationship between Hoy No Circula and annual vehicle registrations (natural log) using a fifth-order polynomial time trend.

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