What are the pros and cons of raising the UK national speed limit to 80mph?

Our current maximum speed limit is 70mph and has been for many years (since 1967). Cars have become increasingly more capable to safely handle speeds above this, and with new technology that can brake automatically, is it time to raise our speed limits? What are the pros and cons?

The problems with an 80mph speed limit

Fuel economy

Cars usually have the best fuel economy at around 50-55mph, above which fuel economy becomes worse (see this example). Therefore more people driving faster equals more pollution. As we have an environmental responsibility to keep fuel usage down, increasing the limit to 80mph would increase fuel consumption unnecessarily. A car uses around 10-20% more fuel travelling at 80mph than it does at 70mph. As we are reliant on fuel imports from other countries, it would not help our balance of trade.

Road design

While on the motorways, driving at 80mph is factored into the design in most places, most other roads aren’t engineered to support safe driving at that speed. It would increase the accident risk.

Accident severity

Simple physics dictates that if you have an accident at 80mph vs 60mph or 70mph you have to dissipate a lot more force, therefore the severity of accidents would increase. This would lead to more costs on the health system and a larger number of people with injuries that might be permanently debilitating.

Assuming the accident rate stays the same, we would see an increase in the number of accidents that are defined as severe. According to these figures from Department For Transport, the cost of a severe accident is almost ten times the cost of an accident with only slight injuries, at £216,203.

Vehicle failure

As it stands, a very low proportion of fatal accidents are caused by vehicle failure; the majority are driver error. For example, in 2011, 26 fatal accidents were attributed (at least in part) to having defective or under-inflated tyres out of 1663 fatal accidents according to this publication (page 75). Let’s make an assumption which may (or may not) have some truth to it: people with limited financial means tend to drive older cars with less safety features and they are more likely to be poorly maintained. Obviously this won’t be the case for everyone, but it seems a reasonable assumption to make.

Vehicles at the margin would be more likely to break down or have catastrophic tyre failure. Fines related to speed limits are an effective control to discourage people from exceeding the limits of their cars. People with fewer financial means perhaps tend to drive vehicles that would be at the margins of safety and performance, leading to a bigger risk of those vehicles failing mechanically, causing an accident. I.e. normal tyres would be at risk of overheating with prolonged driving spells of 80–90mph, especially if they are not at the correct pressure, whereas performance tyres on a more expensive vehicle should be able to handle it.

Increased congestion

Ironically, going faster causes more traffic congestion. When there’s a bigger gap between the fastest vehicles and the slowest vehicles roads clog up quicker which is why we have variable limits now: to reduce the speed of the fastest vehicles so that all vehicles are roughly going the same speed, which gives the most consistent throughput of traffic. The speed differential between lorries and cars would be increased.

Vulnerable road users

This assumes that the 80mph limit also applies on rural roads and dual carriageways. Faster speeds mean less margin of error when dealing with other road users such as cyclists and pedestrians. Faster vehicles create more of a buffeting effect when passing cyclists. Pedestrians would have less time to cross the road if vehicles were going faster and if a vehicle needs to brake hard to avoid a pedestrian or cyclist, the distance required to stop from 80mph vs 70mph is significantly longer, meaning if there’s an impact it will be at a much higher speed.

Driver capability

While newer cars have autonomous and semi-autonomous features such as automatic braking, many cars don’t, but a speed limit must apply to all cars. Poor driving skills are unfortunately rife, and tailgating is arguably the most common. Some people tailgate so closely that if the vehicle in front stopped quickly they wouldn’t even have time to hit the brake to react.

In general, the driving population’s abilities behind the wheel are not good enough to increase the speed limit. Add to the fact that most people spend the majority of their driving time crawling along at low speeds, they are not accustomed to driving at speed. This is often graphically illustrated when an overseas tourist from a high-density city tries to rent a car and drive through rural Wales, and ends up either holding everyone up because they can’t cope with the speed, or driving off the road because they don’t anticipate the road ahead.

It could be argued that much of Europe has a higher limit on its motorways but they are (generally) less congested than British motorways.

Merging

Motorway slip roads are designed to allow vehicles to get up to 70mph (if possible) to match the speed of traffic already on the motorway. If traffic is now travelling at 80mph, then there’s a speed differential of 10mph (or more, because if the limit is 80, people will push it up to 90). Authorities might find that they need to make longer slip roads which will increase construction and maintenance costs.

Conversely, exiting the motorway would see a larger speed differential where a driver must decelerate from 80mph down to 30mph and this could cause problems with speed and danger perception. It also represents increased brake wear and tear.

Are there any benefits of an 80mph speed limit?

An 80mph limit might improve productivity for some people, meaning that they can get to work or between meetings more quickly.

People might find it more fun to drive faster in certain circumstances, leading to perceived improvements in the quality of life.

It’s possible that fewer fines would be issued if people didn’t simply add 10mph to their usual driving speed. Police might not need to do so much enforcement of limits where 80mph is permissible (although this might be balanced with an increased number of accidents).

Could an 80mph limit work in limited circumstances?

If the 80mph limit was variable, it could be applied only on stretches of road suitable for 80mph and only when traffic was sufficiently light that it wouldn’t affect the total throughput. It would be applied only on sunny, dry days where there was no risk of a low sun dazzling drivers. It could be applied only in the overtaking and middle lanes, not the left-hand lane which would be reserved for slower vehicles.