We didn’t have time to strap our VBox timing gear to the NBfL during our test drive, but putting foot flat to floor at Nutts Corner circuit, near Wrightbus’s Ballymena factory, revealed that NBfL is capable of making only sedate, albeit sustained and linear, progress.
Step-off from rest is decent enough; the 4.5-litre Cummins turbodiesel generator provides power to an air compressor (for the brakes and steering), a 75kWh battery and the Siemens electric motor, which lies beneath a raised seating area at the rear, from where it drives the back axle. It makes, as electric motors do, peak torque (of 1844lb ft) from zero revs, so step-off is as brisk as NBfL gets.
The electric motor does all the driving; the diesel generator is tuned to sit at optimum revs and provide all the power the batteries need, and it runs only when those batteries need topping up (which was most of the time during our test, although regenerative braking will assist on a proper bus route). The generator is overly grumbly during stop-start at the moment, but Wrightbus engineers are working on a fix.
Braking is both by the drive motor and pneumatically assisted discs all round; retardation is fine and there’s ABS, but pulling the NBfL to a rapid stop, perched as you are in front of, and mostly below, nearly 20 tonnes of metal, isn’t the most enjoyable thing you’ll ever do in your life.
Ride and handling
Here, then, is where we get to the nub of the Autocar road test: what’s she like to drive?
Seated in the widely adjustable but pretty flat driver’s seat (which does without a seatbelt, incidentally), you get a supremely clear view forwards. The low-set steering wheel is very adjustable, so finding a comfortable driving position is a cinch, but the upright stance and wide chair mean it’s more like sitting at a desk than in a car. The pedals are on the flat floor and the wheel is barely off the horizontal.
Still, foot on the long-travel brake pedal, handbrake off and, as you ease off the pedal, the NBfL creeps forward with eerie smoothness. Never before has a hybrid drivetrain seemed so suited to a vehicle.
It’s hard to gauge the ride across what amounts to a big kart track, but where the NBfL did meet imperfections, it ironed them out pretty admirably. On the road we’d expect the largely comfortable float you get in most buses, but with less of the accompanying crash over bigger potholes thanks to the composite rear end’s body-stiffening properties.
At 2.5 metres across, the NBfL takes up its share of road space, but its turning circle is superb at little more than twice the bus’s length.
Nonetheless, if you haven’t driven a cab-forward piece of kit before, it takes some getting used to: you turn the easy, slick and consistently light steering through its 4.5 turns later than you might think when exiting junctions, to give the ample sides room to clear apexes. But the NBfL’s flat sides mean that its mirrors are supremely effective at letting its driver judge clipping points and gaps. Get into a groove and there’s real pleasure to be had from driving the NBfL smoothly and placing it accurately – even more so because the power delivery is so smooth. The brake pedal could use a little more feel for our taste, though.
Buying and owning
At around £330,000, the NBfL won’t be cheap when it makes full-scale production for 2013, but neither are its competitors: other hybrid double-deck buses cost £300,000, and when you consider the 12 to 15-year lifespan in London (after which each bus might still get sold on), the NBfL doesn’t seem like such bad value.