It’s a pretty drive through the Deception Pass Bridge area in northwest Washington state on a warm, bright July day. The sparkling blue waters meet a crisp azure sky as green trees sway in the wind that ruffles the steep, rocky slopes.

What lies beneath is a different story. The water is deceptive, creating some of the fastest and strongest currents in Puget Sound.

Driving a Peterbilt 579 Epiq Ultraloft sleeper through this area is an enjoyable experience, riding in the well-appointed cab as nature’s delights roll by. The engine’s comforting sound drifts through the cab as the transmission shifts amid the ups and downs of the road. But something familiar is missing. There’s no smell of diesel.

A Cummins X15N engine fed by compressed natural gas sits under the hood, leveraging an automated Endurant 12 speed transmission. The six-cylinder engine offers 400 to 500 horsepower with a peak torque of 1450 to 1850 lb-ft.

The big Pete had no problem pulling a 53’ trailer that scaled at more than 70,000 pounds gross combined weight up and down the narrow road with its tight turns.

There was some trailer tugging when moving from a traffic light. Slamming down on the accelerator pedal from a stop may have had a different result, but I prefer to drive with a gentle foot.

This 579 was equipped with predictive cruise control that learns a route’s topography and uses that knowledge to automatically adjust speed, torque and gearing the next time you are on that route.

When I flicked the switch, it maintained the truck’s speed while climbing up a bridge and downshifted to reduce speed as I drove down the other side.

From a driver’s perspective, a bit of help driving through the mountains is welcome. It won’t make you inattentive but will certainly give you a moment’s rest to face the next sweeping corner, especially on downgrades.

Digital vision system-mirrors

It’s been a while since I hauled a loaded truck on narrow, windy roads with two-way traffic. I was keeping a close eye on my trailer wheels’ off-tracking to make sure they stayed within the lane, not wanting the trailer sliding into a ditch or clipping oncoming vehicles.

I had a helper for this task – the digital vision system-mirrors (DVS-M). The system uses cameras set into the driver and passenger side mirrors. These can be viewed on two large high-definition monitors placed on the A-pillars. It provides trailer tracking that issues a warning when the rear wheels start to wander outside the lane.

The system has night-vision capability and works in inclement weather. I used the DVS-M to keep an eye on the back of the trailer, especially while making turns, but preferred using the traditional mirrors during the drive. I found the monitors with their moving images a bit distracting as I drove, preferring static display from the mirrors. For me, they took some getting used to.

Fuel efficiency

The Bendix Fusion collision mitigation system also helps keep the truck within the lane and applies the brakes when required. I was glad I did not need its assistance during the test drive.

Peterbilt says the CNG fueled truck is 10% more efficient than its diesel counterpart. In my opinion, it drives like a diesel and feels like one and it would be hard to tell the difference if I didn’t know beforehand. Fuel savings are a welcome bonus.

Just like Deception Pass Bridge, the 579 is a pretty sight. It’s what lies beneath that stands out.