The City of London Corporation is looking at implementing a 15mph speed limit in the capital’s Square Mile to help with road safety and reduce pollution.

Experts say that if anything, it will increase pollution levels due to the stop & start nature of the traffic, but road safety charity Brake is backing the plans.

Planning & Transportation Chairman for the City of London Corporation, Chris Hayward says: “90% of collisions that result in death or serious injury involve a motor vehicle. We need bold ideas to make our streets safer”.

Horse and cart

There were 54 people killed or seriously injured on the streets of the City of London last year, and despite the lower 20mph speed limits, the number of these incidents hasn’t decreased, purely because of the record numbers of pedestrians in the City.

A spokesperson for the AA said that lowering the speed limit will have little to no effect on injuries, comparing the traffic speed to that of a horse and cart, and IAM RoadSmart Director of Policy and Research agrees: “There is no real road safety benefit in enforcing a speed limit which traffic seldom reaches”.

The experts also agree that in all likelihood, it will raise pollution levels, which are currently under scrutiny, and therefore used to tax the motorist further.

Practicalities will also play a part; how would they implement the lower speed limit, particularly concerning cyclists? It’s estimated that around two people are killed or injured every week as a result of an accident with a bicycle. The conviction of Charlie Alliston for causing bodily harm through ‘wanton and furious driving’ proves that there is an issue that needs looking in to.

Better investment

Experts say that rather than enforce an unworkable solution, that will cause further problems with pollution levels, that the City of London Corporation should look into making investments in better road safety infrastructure, such as pedestrian crossings, pinch points and speed humps.

A spokesperson for Brake said: “Speed is a critical factor in many deaths on our roads, we welcome any measure that can help make our communities safer; slower speeds save lives and make our streets a more liveable environment”.

In contrary to that, Hampshire County Council stated in June that they would be no longer implementing 20mph limits, as they’d noticed no discernible reduction in road accidents, which would fit with the theory from the AA.

“Changing the limit from a 30mph zone to 20mph reduces the speed slightly, but the majority of motorists travel at 25mph, so there has been a reduction in speed, but not significant”.

Pollution levels

Putting aside the speed vs injury debate, the other argument from the City of London Corporation is that there would be a reduction in pollution levels. Clearly, with traffic taking longer to clear the area, the start/stop nature of traffic, combined with an already overloaded road system, this simply wouldn’t happen?

A study by the Edinburgh Centre for Carbon Innovation (ECCI) in 2013 found similar results; the nature of stop/start traffic at low speeds means that there is an increase in acceleration and braking, coupled with the fact that at such low speed, any motorist would likely to be in a low gear, which would further exacerbate the problem. The optimum speed for minimising vehicle pollution and emissions is actually around 40mph.

However, that’s simplifying it too much, there are further points to be aware of.

If the traffic flow is smooth, then lower speed limits will help with reducing pollution, it’s only when you introduce the stop & start of city driving that it will negate the effect of lower limits. Due to further legislation surrounding emissions, car manufacturers comply with much stricter emissions regulations, and therefore, their products are tuned to give optimum returns under the majority of use – around 45 – 50mph in top gear.

Using traffic-calming measures can work under certain circumstances, but it gets back to keeping the traffic flowing smoothly – not accelerating away from speed humps or traffic lights for example.


While it’s undoubtedly commendable to try and reduce the number of injuries in a locale, there needs to be serious thought given as to how practical this can be, or whether it’s just another publicity/money generating scheme for the local authority.

Evidence and experts say that a 15mph speed limit won’t really affect either positively – it won’t reduce accidents, nor will it help with pollution, so just what is the purpose of lowering the limit? We know the cynical answer, but surely, it can’t be that blatant?

What do you think of a 15mph speed limit? Should more cities introduce it? Should the City of London stop wasting money on schemes to hit the motorist? Let us know in the comments.

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