Policy

The Ever-Bigger Car Problem: What 15 Years of Growth Will Cost Us by 2040

The increase in car size (known as car spreading or car bloat) is drawing growing attention from researchers. This study examined the impact on parking, road safety, and electricity use.

Key Takeaways

• The average length of new cars keeps increasing by 1.2 cm per year, and their average height by 0.5 cm per year.
• This study compares two scenarios for car dimensions over the period 2026 to 2040:
  • Under the prevailing ever-bigger trend (‘Current trend’), the average size of new cars continues to increase in line with trends since 2000.
  • Under a more balanced scenario (‘Right-sizing’), the average size of new cars steadily returns to 2015 levels.
• Parking: Cities are set to lose 8.5% - 14% of their end-to-end on-street parking spaces by 2040 if the current ever-bigger trend prevails.
• Without action to tackle the ever-bigger trend, the loss of parking could translate into support to convert other urban space to parking
• Safety: There are around 2,600 additional deaths of vulnerable road users by following the current ever-bigger trend, including 79 children.
  • Under current trends, 40% more children walking would be killed a year in car crashes by 2040 compared to the Right-sizing scenario
  • For vulnerable road users (pedestrians, cyclists, motorcyclists and moped riders of all age groups), current trends would bring 400 additional deaths annually by 2040 compared to a more balanced scenario
• Electricity: By 2040, the current trend would require an additional 22.5 TWh a year, comparable to 1,500 more onshore wind turbines (compared to Right-sizing), increasing annual household charging bills by €7 billion.
• Policy recommendations:
  • Cap bonnet height in new cars at 85 cm, and limit width to 192 cm.
  • Add vehicle dimensions to vehicle registration certificates
  • Ensure that regulatory advantages only go to small electric cars (not longer than 4.2 metres) in revising car CO2 law
  • Rate the vision of children from the driver’s seat of new cars (Euro NCAP), and apply a Child Vision Standard in law
  • Vary car taxes and parking charges by dimensions.

Comment

It is clearly desirable to incentivise the use of smaller cars compared to larger ones. However, the difficulty is now a political one.

If increased parking charges for larger cars had been implemented 25 years ago, it would have affected only a small proportion of the population. Today, the affected population would be much larger, creating a significant number of 'losers' and making the politics more challenging.

To reduce political controversy, it might be best to start with significantly higher prices and regulations only on the largest cars so that only a small proportion of the population is impacted immediately and expanded over time to cover more vehicles. This would, to some extent, act as a cap on the continued growth in car size.

What Next?

Do you have a policy for tackling ever bigger cars?

Policy

Four Faces of Transport Opinion

Improving the way our transportation systems work depends on community support. This research examined attitudes toward different transport policies in Germany using a survey of 1,700 respondents.

Key Takeaways

• Improvements in public transport are consistently prioritised by 41% of respondents.
• 25% of respondents ranked “Improvements in road traffic” first.
• Reductions in environmental impacts were ranked by 18% of respondents as the most important topic; however, 32% ranked it lowest, indicating polarisation.
• Four distinct preference classes are identified:

1. Public Transport Advocates (26%):

• Display a clear preference for improvements in public transport, particularly on reliability and punctuality.
• 37% of respondents within this class ranked introducing a speed limit as their top environmental measure.

2. Long-Distance Optimisers (15%):

• Respondents in this group appear to prioritise measures that enhance the efficiency of longer trips.
• They most strongly support a CO₂ levy on transport emissions but are notably critical of a general highway speed limit.

3. Car-Oriented Pragmatists (43%):

• Respondents in this class consistently favour improvements in road traffic and reject measures aimed at reducing environmental effects.
• This group supports expanding cycling infrastructure but strongly opposes implementing it at the expense of car parking.

4. Multimodal Interventionists (17%):

• Generally support measures aimed at reducing environmental effects, but 20% of respondents within the class also prioritised improvements in road infrastructure and public transport.
• This is the only group that does not favour expanding cycling infrastructure.

• A conflict line emerges between what could be described as an active–public transport–urban orientation versus a car–rural–restricted pattern.
• How people travel shapes how they perceive, prioritise, and are affected by transport measures.

Comment

These results show the challenges of changing our transport systems. Whilst there is lots of support for carrots in transport (e.g. more infrastructure), there are much more polarised views on the use of sticks.

Preferences are heavily dependent on existing travel behaviours. However, we know that public opinion can change significantly once stick policies, such as congestion charges, are successfully implemented.

For politicians, the key challenge is trying to work out where the public will be after a change has been made - will they change their minds and support the policy?

What Next?

Do you have a good understanding of current public opinion on transport policies?

Planning

Habit, Comfort, and Safety: The Psychology Behind Mode Choice Modelling

Modelling is a core part of transport decision-making. The New Zealand government has produced a report examining how the latest research can help it improve its modelling.

Key Takeaways

• Traditionally, transport mode choice models made predictions using objective factors such as demographics, trip characteristics, travel time, cost, and reliability.
• Recent research shows that psychological factors are also important in understanding people’s travel mode choices. These include attitudes, perceived behavioural control, and subjective norms.
• ‘Hybrid choice models’ combine both objective and psychological approaches.
• The researchers found that hybrid choice models can:
  • improve predictions, meaning more accurate forecasting of travellers’ mode choice
  • uncover causal relationships and give insights into travellers’ mode choices
  • capture differences in mode choice patterns between individuals and groups.
• Habit is another important factor to include for accurate modelling and prediction. Habit strongly predicts mode choice and can outweigh an individual’s intentions.
• We also need further research on innovative modelling of complex travel that includes multiple modes, ‘legs’, users, and trip purposes in a single trip.
• Traveller personas are specific and tailored to individual users, while traveller archetypes show broad transport user types. Archetypes can give a deeper understanding of the psychological factors and motivations in travellers’ mode choices.
• Key psychological factors impacting New Zealanders’ journey experience and mode choices:
  • Habit significantly influences mode selection, especially among frequent public transport users.
  • Safety perceptions heavily influence journey preferences, with cars and public transport viewed as safer than cycling or walking.
  • Perceived comfort and ease of use are vital for journey satisfaction, with cars typically offering superior comfort and control.
• Traveller group types vary in how important they find aspects of travel.

Comment

Whilst there is nothing wrong with improving our modelling, I fear the returns from better decision-making will be small.

The biggest challenges in transport are not from a lack of data or inaccurate modelling; they are almost always political - the views of the public and politicians on the transport solutions they want to see versus what good transport planning requires.

The political arena is where transport research needs to be enhanced.

What Next?

Do you have plans for improving both modelling and understanding of decision-making?

Quick Adventures in Transport Wonderland

Here is what else I came across this week:

• ​Priced Out of the Game - a blog on pricing and demand management at major events.
• ​Exploring the effect of motor traffic on street crime - an article on another unintended consequence of traffic: higher levels of crime.
• ​Netherlands bike planning - a short article on the Dutch approach to bike planning.

Tool

Institutionalizing the Safe System Approach

​This toolkit from National Academies supports institutionalising the safe system approach.

Tool

The Road and Railway Cost Calculator

​This calculator is designed to provide planners and policymakers with quick, reliable cost estimates without requiring specialist engineering expertise or a large budget.