Summary and conclusions

Recorded collision data in Scotland shows that high severity collisions are more likely to have speed recorded as a contributory factor. Drivers of lighter vehicles such as cars and motorcycles are more likely to have been recorded as travelling an inappropriate speed when involved in collisions. Conversely the number of goods vehicles involved in speed related collisions is comparatively low. It has been identified that local authority A roads have the highest accident rates on Scotland roads in 2022. These roads are predominantly single carriageways in rural environments. This highlights that lowering posted speed limits on these routes would be consistent with the Safe System approach.

International research has identified relationships between traffic speeds and collision data. Based upon this, the Nilsson’s power law identifies that significant reductions in fatal and serious collisions can be obtained from reducing vehicle speeds.

Following on from an option generation and option sifting exercise, this report considers two options to change National Speed Limits within Scotland to work towards Scotland’s long-term vision for road safety, Vision Zero, by 2050. The options aim to reduce vehicle speeds and speed differentials between vehicles such that driver decisions are easier to make and when collisions occur the consequences are reduced.

Reflecting upon the evaluation of changes made to the National Speed Limit of goods vehicles (>7.5t) in England and Wales (see section 8.7), it is considered that option 1 presented in this report can be adjusted to include the increasing of the National Speed Limit for goods vehicles (>7.5t) without significantly impacting upon option appraisal outcomes. Accordingly, a summary of the resulting options is presented below.

Option 1

This option aims to improve road safety and reduce speed differential on single carriageways.

  • On single carriageways:
    • Cars and motorcycles would have a decreased speed limit of 50mph; and
    • Goods vehicles (>7.5t) would have an increased speed limit of 50mph.
  • On dual carriageways as follows:
    • Goods vehicles (>7.5t) would have an increased speed limit of 60mph.
  • On motorways:
    • No alterations to speed limits proposed.

Option 2

This option aims to improve road safety and reduce speed differential on Scotland’s Road network.

  • On single carriageways:
    • Cars and motorcycles would have a decreased speed limit of 50mph; and
    • Goods vehicles (>7.5t) would have an increased speed limit of 50mph.
  • On dual carriageways as follows:
    • Cars and motorcycles would have a decreased speed limit of 60mph; and
    • Goods vehicles (>7.5t) would have an increased speed limit of 60mph.
  • On motorways:
    • All vehicles limited to 60mph.

Recognising that future events and outcomes are uncertain, four future scenarios have been considered within the appraisal. These include “with policy” and “without policy” to reflect that government actively implements several aligned policies which may or not be achieved.

The other futures’ appraised considers the level of compliance with speed limits that may be achieved. This has been represented by 100% compliance future and a realistic compliance future. The realistic compliance future assumes that vehicle speeds would be reduced by 2.5mph (4kph). The level of compliance achieved is likely to be heavily influenced by education and enforcement strategies.

The options presented propose to increase HGV speed limits and reduce the speed limits of lighter vehicles with the aim of reducing speed differentials. Considering vehicle interactions and the current poor compliance with existing HGV speed limits, it is the expected that the impact on HGV journey times would be insignificant.

Although the direct benefits of road safety education programmes in terms of collision data and vehicle speeds is uncertain, it is reasonable to assume that if drivers are not educated about changes in National Speed Limits the benefits sought from changing speed limits would not be attained.

Although both options are predicted to facilitate Scotland’s journey to Vision Zero with similarly limited impact upon environmental factors. Option 2 is likely to have a significant adverse impact on the economy, whereas this is not expected for option 1.

Next Steps

To fully understand the implementation of the options considered by this report, a comprehensive stakeholder engagement exercise is recommended. This would include key stakeholders such as Police Scotland, Local Authorities and the Road Haulage Association.

To demonstrate the impacts of the options being realised it is recommended that monitoring strategy be defined and implemented. This should take cognisance of the STRIPE framework.

To obtain the maximum benefits of the options, it is recommended that a compliance strategy is defined and implemented.

Ensuring public awareness of changes in National Speed Limits is considered critical to obtain the benefits associated with the options. It is considered that implementation of the options via changes in legislation combined with appropriate publicity would achieve maximum driver awareness.

Guidance documents are used to inform the setting and enforcement of speed limits in Scotland. This guidance will require to be identified, reviewed and updated as part of the implementation of the options.