What Bus Depots Need to Know about Euro Emission Standards

In this blog, we’ll unpick the Euro 4 vs Euro 5 vs Euro 6 debate so your bus depot can consider some important real-world challenges before purchasing your next engine upgrade.

Euro emission standards are a set of regulations established by the European Union (EU) with the aim of reducing harmful air pollution from vehicles and improving public health. Since its inception in 1992, seven regulations (Euros 1 to 7) have had a significant impact on the market. Each step up in standard reduces allowable emissions, including:

Although the UK has left the EU, Euro emissions standards continue to be important, ensuring continuity in standards.

Keeping your fleet clean with the right engine can help minimise emissions and give your brand a stronger reputation. With this in mind, let’s weigh up some different Euro emission standards.

When selecting an engine upgrade for your fleet, consider the differences between Euro 4, 5, and 6 emission standards. Let’s break this down.

Euro 4 Emissions Standards:

Introduced in 2005, Euro 4 marked a significant reduction in NOx and PM emissions compared to Euro 3, mostly achieved through Exhaust Gas Recirculation (EGR).

Engine Pros:

Engine Cons:

Best for:

Euro 4 may be the best option for short-term fleet expansion or rural routes where emissions regulations are less stringent.

Euro 5 Emissions Standards:

Introduced in 2009, Euro 5 further tightened particulate matter (PM) limits and introduced readiness for Diesel Particulate Filters (DPFs), although not all vehicles were equipped with them.

Engine Pros:

Engine Cons:

Which is better, Euro 4 or Euro 5?

Euro 5 has stricter specifications, which can lead to reduced emissions. If you have a transitional fleet looking to upgrade incrementally or a bus depot operating in semi-urban areas, Euro 5 is a better option. Euro 6, however, takes things one step further.

Euro 6 Emissions Standards:

Introduced later than Euro 4 and 5 in 2014, Euro 6 definitely wins the Euro 4 vs Euro 5 vs Euro 6 debate, drastically reducing NOx and mandating advanced after-treatment systems such as Selective Catalytic Reduction (SCR) and DPFs. Euro 6 emissions standards help us move further away from the myth that diesels are dirty!

Engine Pros:

Engine Cons:

Is it worth buying a Euro 6 diesel?

Purchasing a newer diesel model will reduce your chances of getting penalised in cities. Euro 6 vehicles are a solid option for high-mileage fleets and depots looking to upgrade and futureproof themselves, especially those tackling urban routes through environmentally conscious cities.

Explore the table below for a comparison of Euro emissions, with the most significant change being the 68% reduction in NOx limits from Euro 4 to Euro 6.

You can check your vehicle’s Euro emissions rating on the V5C logbook document. Additionally, you can utilise a free tool available on the government website to assess your vehicle’s emissions based on its registration. This will help you uncover if you will be charged to drive in Clean Air Zones.

Taking note of Euro emissions standards is critical, especially as the government aim to ban the purchase of petrol and diesel cars by 2050 in its Road to Zero strategy. This means your fleet needs to be conscious of its emissions and adapt to the changing standards to stay ahead.

There are several factors to weigh up when investing in a new engine aside from Euro emission standards. As well as the pros and cons we’ve outlined above, take note of the following factors:

As expected, being the oldest, Euro 4 vehicles are the most affordable. Euro 6 vehicles are more expensive, armed with the newest engine technologies. Despite this higher initial cost, this may pay off in the long run, which could make all the difference for your fleet. Factor in fuel use, maintenance, and compliance costs to gain a broader perspective.

More advanced systems compliant with modern Euro 6 standards will typically retain their value longer than those compliant with Euro 4 and 5 standards. This can be important when it comes to resales.

Regions are increasingly imposing low- or zero-emission zones, which effectively limit and ban older engine types. Consider your fleet’s routes – Euro 6 emission standards are a must if you operate in or near low-emission zones.

Euro 6 vehicles typically require AdBlue and routine servicing of their emission control systems, so you need to consider whether your company can support these requirements.

Putting Euro emission standards aside, a more innovative engine will likely result in a more innovative performance. This can help your fleet stay productive, on time, and less likely to run into frequent diesel engine problems. Learn more about why engine quality is important for bus fleets and how to keep your engine in good condition.

You can technically upgrade a Euro 4 to a Euro 6, although it is often complicated, expensive, and impractical. After all, contemporary Euro 6 vehicles are designed around emissions control from the ground up, meaning that adjusting an older Euro 4 vehicle can often fall short of the required standard.

Your best alternative would be to replace your old Euro 4 vehicle with a Euro 6 vehicle. If your company is worried about covering costs, second-hand and remanufactured engines are always options. For example, our team is well-versed in remanufacturing Euro 6 engines, and keeping your fleet well-stocked with these can have its benefits.

Euro 7 is scheduled to hit our roads in late 2026 with even stricter standards than Euro 6. Euro 7 will impose emission limits on all vehicles, including electrics. One of the biggest differences between Euro 6 and Euro 7 will be the latter’s focus on decreasing non-exhaust emissions related to brakes and tyres, including microplastics.

So, that’s a wrap on our Euro 4 vs Euro 5 vs Euro 6 debate! Euro 6 emission standards are currently leading the way, although it’s important to weigh up all your fleet’s options when planning your next engine upgrade.

Here at Foxwood Diesel, we have been a key supplier to the truck, bus, and coach industries since 1988 and can assist you with all your Euro diesel engine needs. We know them inside out and can get them back up and running quickly and cost-effectively.

In addition to bus and coach engine repair or replacement, Foxwood Diesel also stocks a comprehensive range of new and reconditioned Cummins parts, available for overnight delivery. Contact us for more information about our services and how diesel engines work, or to address a question regarding Euro emission standards.