Driving Restrictions: Pollution Solution Or Not?

Driving restrictions are one of the most commonly adopted measures to curb air pollution. These restrictions are based on the last digit of a vehicle's license plate, with some cities banning a fifth of vehicles from entering. While these restrictions aim to reduce congestion and air pollution, their effectiveness is questionable. Some studies show that driving restrictions reduce local pollution and congestion, while others find no significant impact or even negative consequences, such as an increase in the number of vehicles on the road. An example is Mexico City's Hoy-No-Circula program, which led to some households purchasing older and more polluting second cars. Other alternatives, such as congestion charging schemes, aim to reduce car-use dependency and encourage the use of public transport or active travel.

Effectiveness of driving restrictions

The effectiveness of driving restrictions in reducing pollution depends on a variety of factors, including the specific design of the policy, enforcement, and local behaviours and conditions.

One of the most common types of driving restrictions is license-plate-based restrictions, which keep private vehicles off the road on certain days of the week based on the last digit of their license plate number. These types of restrictions are particularly popular in Chinese cities, with over 86 million people affected across more than 30 cities. Research on the effectiveness of these policies has yielded mixed results. Some studies have found that license-plate-based restrictions reduced local pollution and congestion, while others found no influence or mixed results, with initial short-term reductions but no long-term effects.

The literature also reveals that drivers often exhibit behavioural responses to driving restrictions that can reduce their effectiveness. For example, households may choose to drive during unrestricted hours, violate the policy, or rearrange their trips to other days. The "second-car hypothesis" suggests that license-plate-based restrictions can backfire by encouraging households to buy a second car, leading to increased local pollution. This hypothesis is supported by studies in Mexico City and Bogotá, which found that driving restrictions did not improve air quality and, in some cases, led to the purchase of older, more polluting vehicles.

However, driving restrictions can also have positive effects on reducing pollution. For example, they can increase the use of alternative transportation options such as bikeshare programs during peak commuting hours. Additionally, exemptions for low-polluting vehicles can help reduce pollution and modernise the vehicle fleet. Overall, the effectiveness of driving restrictions depends on a complex interplay of factors, and policymakers must carefully consider potential behavioural responses when designing and implementing such policies.

Low-emission vehicles and exemptions

Low-emission vehicles are those that produce fewer emissions than the average vehicle on the road. Examples of low-emission vehicles include the Honda Civic Hybrid, the Nissan Altima, the Toyota Camry, and the Prius hybrids. These vehicles are often designated as SmartWay or Low-Emission Vehicles (LEVs). LEVs are defined as vehicles that emit fewer pollutants than the average vehicle sold in a particular year.

Ultra-Low-Emission Vehicles (ULEVs) are 50% cleaner than the average new model vehicle, while Super Ultra-Low-Emission Vehicles (SULEVs) are 90% cleaner. Partial Zero-Emission Vehicles (PZEVs) have zero evaporative emissions and a 15-year/150,000-mile warranty. Advanced Technology PZEVs (AT PZEVs) are compressed natural gas or hybrid vehicles that meet SULEV standards for tailpipe emissions and include advanced technology components. Zero-Emission Vehicles (ZEVs) have zero harmful tailpipe emissions and are 98% cleaner than the average new model-year vehicle.

Exemptions for low-polluting vehicles may help reduce pollution and modernise the vehicle fleet. However, they may also result in an increase in the number of vehicles on the road, leading to added congestion. In some cases, households may choose to purchase a low-polluting vehicle that is exempt from driving restrictions. This could potentially increase local pollution if households decide to buy a second car, as has been observed in some studies.

To encourage the use of low-emission vehicles, governments and organisations have implemented various initiatives and grants. For example, the US Federal Transit Administration (FTA) announced the availability of $1.5 billion in grants for low- or zero-emission buses and supporting facilities. Additionally, the Low or No Emission Grant Program offers funding for workforce development and training related to zero-emission vehicles.

Behavioural responses to restrictions

Driving restrictions based on license plates have been implemented in various cities, including Chinese cities, Delhi, and Mexico City. These policies typically restrict vehicles from being used on certain days within cities based on the last digit of their license plates. While these policies aim to reduce pollution and congestion, they have received mixed responses, with some studies showing reductions in local pollution and congestion, while others found no significant influence or only short-term effects.

Behavioural responses to these restrictions play a crucial role in their effectiveness. Here are some of the ways in which households and drivers respond to such driving restrictions:

• Switching travel modes: Households with restricted cars may choose to drive during unrestricted hours or rearrange their trips to unrestricted days. This strategy was observed in Delhi, where around half of the affected drivers lawfully bypassed the restriction by switching to unrestricted private travel modes.
• Ignoring or violating the policy: Some households may choose to disregard the driving restrictions and continue driving on restricted days.
• Vehicle purchase decisions: Households may opt to purchase a low-polluting vehicle that is exempt from the restrictions. This can lead to the modernisation of the vehicle fleet and a reduction in pollution. However, it may also result in an increase in the total number of vehicles on the road, adding to congestion.
• Buying a second car: The so-called "second-car hypothesis" suggests that households might respond to restrictions by buying a second car with a different license plate, allowing them to drive unrestricted. This could potentially increase local pollution and counteract the intended benefits of the policy.
• Alternative travel days or times: Drivers may choose to take car trips on different days or at different times to avoid the restrictions. This behaviour can reduce the success of the policy in decreasing congestion and pollution.
• Exemptions and enforcement: Policies with exemptions for certain vehicles or areas, such as outside central city regions, can lead to increased driving on restricted days. Improving enforcement and discouraging undesired behaviours are crucial for the efficacy of these regulations.

Driving restrictions and congestion

Driving restrictions are one of the most commonly adopted measures to curb air pollution. These restrictions are based on the last digit of a vehicle's license plate and are popular in Chinese cities, with over 86 million people affected by the policy across more than 30 cities. Other cities that have implemented such restrictions include Mexico City, São Paulo, Bogotá, Santiago, San José, Quito, and Delhi.

While driving restrictions aim to reduce congestion and air pollution, their effectiveness is questionable. Research on the impact of driving restrictions on congestion and pollution has yielded mixed results. Half of the studies reviewed by Guerra and colleagues found that license-plate-based driving restrictions reduced local pollution and congestion. A quarter of the studies found that the restrictions had no influence, while the remaining quarter showed mixed outcomes, with initial short-term reductions but no long-term effects.

The literature suggests that driving restrictions can lead to behavioural changes that may reduce the success of the policy. For example, households may choose to drive during unrestricted hours, violate the policy, or rearrange their trips to unrestricted days. Some households may even opt to purchase a second car, which is often an older and more polluting vehicle, as seen in Mexico City. This "second-car" effect increases fleet size and moves the composition towards higher-emitting vehicles, resulting in more congestion and pollution over time.

Furthermore, banning a portion of vehicles from cities does not guarantee a proportional reduction in congestion or pollution. This is because private cars make up only a fraction of total traffic, and traffic pollution is just one aspect of local pollution. The effectiveness of driving restrictions is also influenced by policy design, restriction enforcement, and local behaviours and conditions.

To address the limitations of driving restrictions, some cities have introduced exemptions for low-polluting vehicles. However, this approach may lead to an increase in the total number of vehicles on the road and contribute to congestion. Congestion charging schemes have been proposed as an alternative to driving restrictions, but they are often challenging to implement and expensive to administer.

Driving restrictions and bikeshare usage

Driving restrictions based on license plates have shown mixed results in reducing pollution. While some studies show a decrease in local pollution and congestion, others indicate that such restrictions have no influence or may even lead to increased pollution due to households buying a second car or driving during unrestricted hours. To improve the effectiveness of these policies, policymakers need to address behavioural responses and enforce measures that encourage desired behaviours.

Bikeshare systems offer an alternative mode of transportation that can help reduce pollution from motor vehicles. Cities like Boston have implemented bikeshare programs like Bluebikes, which aim to provide a reliable and inexpensive way for residents to commute and contribute to greenhouse gas reduction goals. During the COVID-19 pandemic, bikeshare usage increased in cities like New York and Budapest due to government restrictions and a preference for non-motorized transportation. However, after the restrictions were lifted, bikeshare ridership declined, indicating that permanent behaviour changes were not widespread.

To promote biking as a mode of transportation, cities like Boston are collecting and analyzing data to improve bike infrastructure and safety. This includes pursuing priority routes with dedicated bike lanes and retrofitting streets to slow down traffic. By supporting bicycling and improving infrastructure, cities can enhance the convenience and safety of biking, making it a more attractive transportation option for residents.

Additionally, individuals can contribute to reducing pollution from motor vehicles by making smarter choices. This includes driving fuel-efficient vehicles, maintaining proper tire inflation, observing speed limits, and reducing unnecessary idling. These simple actions can significantly reduce air pollution and improve overall fuel efficiency.

In conclusion, driving restrictions may have varying effects on pollution levels, and to enhance their effectiveness, policymakers must address behavioural responses. Promoting bikeshare systems and improving bicycle infrastructure can provide an attractive alternative to driving, helping to reduce pollution and congestion. Individual actions, such as choosing efficient vehicles and driving responsibly, also play a crucial role in lowering pollution from motor vehicles.

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