How 30mph makes a difference

Driving at 30mph instead of 40mph rarely changes journey times, because volumes of traffic at traffic lights and junctions cause most delays.

In free-flowing traffic, driving 10mph slower adds only 10 to 30 seconds per mile, a small delay for a huge safety benefit.

Slower speeds save lives

• Speed is a factor in around 30% of fatal collisions in the UK.
• Vulnerable road users including children, older people, cyclists, and those with disabilities are most at risk.
• In 2022, fatality rates on 40mph roads in England were nearly twice as high as on 30mph roads (per mile travelled).

Research shows:

• every 1mph reduction in average speed can cut collisions by around 5%
• reducing limits from 40mph to 30mph could cut collisions by up to 50%
• a 1mph reduction on urban roads can reduce traffic deaths by around 6% (World Resources Institute)
• on some Birmingham roads, this could mean up to 60% fewer fatalities

Crash severity also drops:

• at 40mph, a pedestrian hit by a car has a 90% chance of being killed
• at 30mph, the risk falls to around 20% (Roadwise UK and THINK! campaign)

Health and wellbeing benefits

Lower speeds make streets safer, calmer, and more pleasant, especially for people choosing to travel actively by:

• walking
• wheeling
• cycling
• using public transport

The more people are able to lead more physically active lifestyles, the greater the public health benefits. Physical activity is one of the most effective ways to boost wellbeing.

Evidence shows:

• reducing speeds by 10mph can lead to a 12% increase in people choosing to walk and cycle as part of their daily routines

Additional benefits

Fuel efficiency

Driving smoothly at steady speeds saves fuel and reduces wear on vehicles.

Air quality

Lower speeds reduce emissions. Transport for London research shows nitrogen dioxide levels fell by 15 to 20% in pilot areas.

Traffic flow

Slower, consistent speeds reduce stop-start driving and congestion. Department for Transport research shows that when speeds are similar, peak-hour travel can improve.

Safer roads also encourage walking and cycling, reducing short car trips and improving public health.

Impact on businesses

Lower speed limits have little or no effect on journey times. Research by Transport for London shows:

• speed reductions do not require changes to bus timetables
• traffic signals and passenger stops affect bus travel times, not speed limits.

Impact on emergency services

Emergency service vehicles can legally exceed speed limits when responding to calls. This scheme will have no impact upon response times.

Page last updated: 19 December 2025