With rising concerns of the effects of emissions on air pollution and greater awareness of what we're pumping out the back of our cars, hybrids have often been held up as part of the solution. The promise of reduced emissions, the absence of range anxiety and tax breaks for company users has seen heads and hearts turning away from diesel.

Lexus uses a self-charging system; a hybrid setup that was introduced by the Toyota Prius over 20 years ago. But does this system in the Lexus RX L deliver on the promises of cleaner motoring for a greener future? 

Seven seat SUV design 

Take the Lexus RX - the largest of the Lexus SUV trio - and extend it, giving space for an extra row of seats in the rear. That's what the Lexus RX L is: a seven seater, pitched directly towards those who might want to split up children two and three to stop them fighting in the second row, or wanting the extra flexibility to transport other kids home from school.

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This is where much of the appeal lies. The list of seven-seat hybrids runs to the Volvo XC90 and that's about it. Other notable seven seaters - Discovery Sport, Kia Sorento, for example - don't come as a hybrid and the pure electric Tesla Model X is considerably more money (while introducing other issues such as range anxiety and charging complexity for certain urban dwellers). But let's hold that thought on these alternatives for a moment.

From the exterior, the Lexus RX L manages to pull off its particular breed of futuristic motoring. It looks interesting, different enough from the growing number of Skoda, Seat, VW, Audi models to make it distinctive. It's also a rarer breed, swinging in with that Lexus quality, something a little more premium than common rivals. 

But that third row doesn't make this a super Uber XL choice. The third row is compact, only really saved by the ability to slide the second row forward to give rear passengers legroom, meaning the second row is then smaller too. It's also a bit of a squeeze to get yourself into that back row of seats. But there are climate controls, cup holders and the seats are of high quality - there's just not a lot of space for knees.

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Yes, it's all about compromise with that third row probably best to accommodate a couple of 12-year-olds - any younger and child seats would add too much lift, any older and headroom becomes a bit of a problem. Ok, so that might be a bit disingenuous: for temporary transportation it's fine, but it can't compete with the third row of the full-sized Land Rover Discovery, for example.

Fold these seats flat and you have a capacious boot, with the unique ability to hide the rolling parcel shelf under the floor for easy stowage. There's no lip so loading is easy, even if you might be left with the feeling that those rear (unused) seats are eating space you could otherwise be filling with luggage.

Big SUV charms

Fitting its premium positioning, soft-touch materials are used and there are details like a wood and leather steering wheel, and wood grain finishes to make the RX stand out. It's not all black plastic, although the two-tone brown as displayed here might not be to all tastes.

Those in the front seats, naturally, get the best that Lexus has to offer. There's a lot of space in the cabin, with little touches like an adjustable depth cupholder in the centre console and door cargo bins that you can fold out to take more, making them really flexible. Little details add to the charms, alongside a centre stowage bin that houses a range of power sources - USB and 12V - but is also big enough to store, as we found, a DLSR camera with lens attached.

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The seats also offer cooling and heating - extending heating to the second row too - so there's an appreciable level of luxury to be had here. That's ideal for long trips and after many hours and some 500 miles into a drive across Europe that comfort was still evident. Simply put, the Lexus RX L is a great place to be.

There is also no transmission tunnel jutting into floor in the second row. That's because of the hybrid setup with the rear wheels powered by the electric motor when needed. This adds to the sense of interior space, giving you a more viable middle seat, or somewhere extra to stow a bag.

The truth about the self-charging hybrid

The biggest thing you need to accept about self-charging hybrids is what does the charging. In this case, it's the 3.5-litre petrol engine. While regeneration from braking adds to the battery (as it does in all EVs and PHEVs), most of the time you'll be using the engine to top-up the battery power. That's what self-charging means.

As a result, the battery in the Lexus RX L isn't as large as you'll find in plug-in hybrid (PHEV) models like the Mitsubishi Outlander. While PHEV SUVs will offer you around 30 miles of range, the Lexus won't even manage that. The hybrid setup on the Lexus, as it is with many of Toyota's cars, is designed to allow engine-off motoring in particular conditions. That tends to be when stopped in traffic or in slow-moving traffic jams, when reversing or parking, or when slowly manoeuvring the vehicle.

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That makes some sense. There's nothing quite like getting into your car and silently pulling away first thing in the morning. You can drive around an underground car park or do that collection from school without the main engine on. You can force the RX into EV mode with the press of a button, but it is limited - and as soon as you hit 40mph the engine will swing in and take over - and the battery-only performance isn't as spritely as dedicated electric cars, only offering a couple of miles of battery motoring.

So the Lexus RX L is really a petrol-powered SUV with some battery benefits, without going the whole hog and giving you the freedom to do your daily motoring emission free. Lexus would certainly benefit from offering a plug-in option, especially as Toyota now offers a plug-in Prius, it doesn't seem so far-fetched an option.

As to the real-world performance, the uncomfortable truth is that the fully-loaded RX L (four passengers plus luggage) on the motorway will average about 32mpg. That's not great and certainly doesn't match many diesels in terms of fuel economy (accepting that emissions are a separate argument), while a fully fuelled Lexus RX L only gives you about 350 miles of range. In that sense, when it comes to motorway cruising, this hybrid setup isn't competitive.

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We also said bear in mind those alternatives, because that 350 mile range is about the same as you get from a Tesla Model X. Yes, there's a huge purchase price difference, and while you can fill-up with unleaded in couple of minutes and be on your way, when it comes to range, it's not that different. Do that enough times and the fuel cost savings will be considerable.

In urban environments the Lexus RX L fairs better. The stop-start driving boosts the battery and in short journeys you have an obvious advantage over diesel - cold diesel engines on short journeys are about the worst of all worlds and here the Lexus' setup feels smooth and easy and you'll see the average rise to closer to 40mpg - but it's short-lived and the longer-term averages for this 450h sit closer to 30mpg. 

In the driving seat 

Behind the wheel of the Lexus RX L is a very nice place to be. Comfort and a great level of finish adds to the occasion and those moments of silent motoring add to the sophistication of the experience. Keyless entry and that huge central display add to the sense of technical sophistication, although there's still a lot for Lexus to improve on, which we'll come to in a moment.

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The ride is soft but not wallowing, soaking away uneven surfaces for a refined drive, avoiding the jarring sports suspension that many SUVs now seem to have. There's also great sound dampening, bringing interior calm, with only a little wind noise coming from the mirrors once you're up at 80mph.

The 3.5-litre petrol engine supplies 259bhp, boosted to 308bhp from the full hybrid system. The battery and the electric motors can swing in to provide more power on demand during acceleration, as well as powering the dynamic torque all-wheel drive, bringing the rear wheels into play when more grip is needed. Powering up snowy roads in the Alps put this to the test, providing assuredness in tricky conditions, but Lexus doesn't position the RX L as an offroader - there's no 4x4 mode, for example.

Put your foot down and the Lexus will throw itself towards the horizon, although it has a CVT - continuously variable transmission - gearbox that doesn't feel as sporty and satisfying as the you'd get from something like the Audi Q7's tiptronic gearbox (notably, there's currently no longer an e-tron version of Audi's seven-seater). The Lexus is wonderfully smooth at slower speeds, so well suited to urban driving, but pull onto the German autobahn and put your foot down and the sophistication drops, accompanied by the strained tones of that petrol engine at 5000rpm.

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There's no support for Android Auto or Apple CarPlay, but you do get support for audio and calls once connected via Bluetooth, or media player support with cable. In this sense Lexus is going its own way. And it's not great.

While the display looks good with a big space for mapping and navigation, it's obviously too far away to touch, so control is via a nubbin in the centre. This works sort of like a computer mouse, letting you move and click, but it lacks the convenience of systems like Audi's MMI or BMW iDrive - it's too easy to miss what you wanted to select. All the time you're trying to do these things, you're not watching the road.

The satnav also isn't hugely sophisticated and while it will find locations and give you a big view when driving, it's just not as easy or dynamic as something like Waze to understand at a glance.

Overall the user interface feels like it's ready to be updated - just as we've said of a recent raft of Lexus cars, including the top-end LC500. Plus, with the voice control not being accurate enough to be natural - Alexa and Google Assistant have changed the standard here - support for smartphone-based systems can't come soon enough. They have been mooted by Lexus, but there's no timeline as to when they might appear.

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One highlight in the technology, however, is the 360 degree camera system. It's not unique, but being able to press the button to see whether you're in a parking space, or how far from a corner you are, really makes detailed manoeuvres easier. There's also a number of safety systems, as well as road sign recognition. Driving across borders we found the road sign recognition really useful for keeping a check on speed, even if the heads-up display (HUD) doesn't automatically change from miles to kilometres once you're on the continent. 

The HUD is also really useful for managing the adaptive cruise control - something that driving on the French Autoroute really benefits from to avoid any tickets - and the lane-keep assistant, which will steer the car round corners and keep it in lane, with a steering wheel button to engage and disengage. Together, they make long distance driving a little more relaxing and both work really well.

Verdict

There's no avoiding the issue that cars are at a fork in the road, both in terms of what people want - SUVs - and how they want them to be powered - cleanly.

Lexus offered hybrid long before anyone else had even thought of the technology and along with the tax breaks, this type of self-charging hybrid might have some appeal if you don't have anywhere to plug it in and want a plush and roomy SUV.

But for all the sophistication and comfort that the Lexus RX L offers on long drives, it lacks the range economy to really make sense driven like that. Great for the school run, a little more costly for the school holidays, where a conventional diesel would be cheaper on the pocket to run, just not on the environment.

Ultimately, the Lexus RX L lives up to the luxury levels you expect. It's a great place to be, a sumptuous way to travel, offering a great drive in most conditions. But that fork in the road is looming ever closer - with the Audi e-tron imminent, for example - and we can't help feeling that right now a plug-in RX would make a lot more sense.