Costs and benefits for 3 options for implementing 20mph limits in Scotland

Summary of Costs and Benefits of 3 Options for Scottish Road Speeds – The Impact of the 20mph National Default Limit

We give our best estimates of the options for rolling out 20mph limits across Scotland. The country will have the benefit of learning from the success of other country 20mph/30kmh implementations, especially England where 25% of the population lives in local authorities who are or have already implemented 20mph limits for most roads. But Scotland can follow the "English" way by implementing authority by authority subject to local political support and funding, or take a more radical and cost effective route by making a national plan for country-wide implementation.

This allows the avoidance of the need for repeater signs on 20mph roads and simplifies the whole implementation process. Local authorities will still be able to nominate roads which will remain at 30mph as exceptions.

Here we present our best estimates of the cost and benefits for each. Transport Scotland will be well placed with its access to street and road detail to produce a more accurate costing and we would be pleased to work with them on such an exercise.


Option Zero. Do Nothing. Keep 30mph limits

Option A: Scottish National Default 20mph limit for Urban Roads (assumes 15% fewer casualties)
Reduction in casualties vs Option Zero

Option B: Local Authority by Authority 20mph localism (assumes 50% of councils at 20mph & 15% fewer casualties)
Reduction in casualties/costs vs Option Zero

Casualties pa on 30mph roads (base is 2011-2015 ave)

49 deaths, 823 serious, 5,410 slight 6,282 total

Casualties saved 7 deaths, 123 serious, 812 slight, 942 total

Casualties saved 4 deaths, 62 serious, 406 slight, 471 total

Casualty £ pa

£267M cost

£56M saving

£28M saving

5 year casualty £ Saving vs Option Zero


£280M saving

£140M saving

Implementation Comment


Default sets majority of urban roads to 20mph with LAs able to raise limits on selected roads to 30mph where warranted.

Patchy risk and casualty reduction effects for ‘lucky few in a postcode lottery’ based on the history of local political support & funding for 20mph in each LA.

Inactivity Cost/ Benefits

Health costs of inactivity. This is currently estimated at £1,153M pa based on Public Health England stats for the Scottish population

Assuming a very conservative effect of reducing this by 1% over the whole population the saving is £11M pa or £55M over 5 years

Assuming a very conservative effect of reducing this by 1% over half the population the saving is £5.5M pa or £27.5M over 5 years

5 year casualty and inactivity saving




Direct Costs to Local Authorities (LAs) / Gov’t


Approx. £4.5M from Gov’t. Replace 30mph with 20mph signs on entrances to communities and 20/30 signs for any roads left at 30mph. No requirement for repeaters.  Plus National engagement and ads £0.5M.  In total approx. £1 per head of Scottish population. We ask Transport Scotland to provide accurate costing.

£8.6M for 50% of urban Scottish population outside Edinburgh (1.925M people). Implemented slowly, as funds become available, funded by LAs. (Estimated costs are based on Edinburgh where it cost £2.2M (£4.46 per head) to sign 80% of Edinburgh’s roads at 20mph).

FYRR and 5 year Benefit to cost ratio


1,100% FYRR on casualty reduction and 67:1 benefit to cost ratio over 5 years on casualty and inactivity reduction.

325% FYRR on casualty reduction and 19:1 benefit to cost ratio over 5 years on casualty and inactivity reduction.


Litigation risks from poor air quality and spiralling social care costs. Vulnerable are unprotected. This option also creates the greatest transport and health inequality.

Consistency improves compliance and casualties saved. Potentially hundreds of life years saved due to more physical activity and improved air quality.  Dominant option for active travel (heart disease and obesity), lower noise levels, greater social inclusion, greater community cohesion and local business viability. 

Benefits of reducing avoidable risks in selected places. Higher levels of activity and exercise & better quality of life, improved air quality vs Option Zero. Lower total benefits and higher total costs than Option A. Takes longer to implement than Option A.

5 yr Summary

Not recommended

Net £330M saved vs Option Zero – The dominant and recommended option

Net £159M saved vs Option Zero, but not as cost effective as Option A.

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