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What will a switch to imperial units mean for UK infrastructure projects?

06 June 2022

ICE Fellows Tim Chapman and David Hirst outline the implications that switching to the imperial system for goods could have on the UK infrastructure sector. 

What will a switch to imperial units mean for UK infrastructure projects?
The old imperial units operated on various bases – often base 12. Image credit: Pam W/Shutterstock

Since antiquity, a realm having a consistent and trusted set of weights and measures has been a key component of national governance.

These units are essential for so many aspects to enable any economy to function smoothly and efficiently.

UK law currently requires metric units to be used for all trade purposes, with very limited exceptions.

The UK government’s recent consultation on reviewing the choices available to businesses in terms how they measure goods could pave the way for greater use of imperial measurements.

The question now about whether the civil engineering and infrastructure industries should revert back to imperial units is therefore a very big deal.

Consistency is key

We now know there are seven fundamental base units (length, mass, time, electrical current, temperature, amount of substance and luminous intensity).

In turn, the internationally agreed standards system (SI) has set these on fundamental physical characteristics – used in almost every country on the globe (except one, and possibly now, two).

As an applied science, civil engineering works with these base and derived units to understand and communicate the behaviour of the materials we work with.

The old imperial units operated on various bases – often base 12, which made halving and then quartering of a length easier.

Meanwhile, the SI system is all in base 10, which makes it much easier for arithmetic calculations, such as those that civil engineers do.

Further, the units are related, so a litre of water has a mass of a kilogram – an especial boon for geotechnical engineers.

Conversely, imperial units often have very irregular conversions, so while there are 16oz in a pound, there are 14 pounds in a stone – odd relationships now remembered generally by people who have retired.

A global economy

The UK is a very international economy, trading extensively with the whole world and so consistency in those markets is vital – the realm we now operate in is global.

British designers have punched above their weight internationally for many decades, assisted by their ability to work nimbly to a range of global codes.

This has put the UK in a strong position to influence the development of global engineering standards, while the US, despite its huge economic muscle, often struggles to gain the same traction.

The British Standards Institution (BSI) as custodian for that global expertise and reputation continues to succeed.

As we enter a fresh phase of frenzied competition for the best new standards to usher in a new ecological age, it’s vital that the UK voice remains prominent and trusted.

Operating in global markets

British manufacturers operate in global markets – none more so than for infrastructure products, where everything from trains to power stations are internationalised commodities.

The UK as both an importer and productive exporter benefits from the opportunity to partake in these highly global supply chains. It reaps benefits in terms of access to the latest technologies and economies from using these international components.

As we push for more modular and manufactured content to make our constructions cheaper, better, quicker and greener, consistency of units becomes ever more important.

Safety must be paramount

Modern engineering systems are highly complex and difficult to integrate, with too many opportunities for misunderstanding and miscommunication.

This can lead to errors, potentially leading to difficult rework, additional expenses and/or delays. In particular situations, it can lead to public safety issues caused by confusion.

Making this situation worse by the introduction of a parallel system of units will lead to more project delays and cost overruns. Potentially in some situations, it could also compromise safety – possibly in quite serious ways.

A full review of the safety implications would need to be held before imperial units could be countenanced as equivalent units for engineering design.

The authors are very sympathetic to some imperial units remaining. The pint has been esteemed for millennia and nothing is quite as disappointing on a sunny day as a half-litre of fluid that somehow is never quite enough.

But a wholesale switch to imperial units for complex engineering calculations will carry costs and safety risks. Those implications must be carefully considered before any switch can take place.

  • Tim Chapman, Partner and Director at Boston Consulting Group
  • David Hirst CEng FICE, managing director at Ainsty Risk Consulting