When we drove the 2014 Silverado, we had the opportunity to try the back seat of the new double cab model. This new layout sits between the returning regular cab and crew cabs in the lineup, and replaces the extended cab. The decision to move from a rear-hinged rear door -- one that requires the front door to be opened to access the rear seats -- to a front-hinged door makes sense. While this makes it a lot easier to get into the rear seat, there are other issues involved with extended cabs, and we're wondering if this is the beginning of the end for that layout.

As far as cab layouts are concerned, the hottest segment of the pickup truck market is the crew cab. While the numbers vary based on manufacturer, crew cabs typically make up nearly 60 percent of half-ton and compact/midsize truck sales. Crew cabs offer more interior space than extended cabs do, and it's easier to access gear and get into and out of the back -- especially when the truck is parked near a post or another vehicle. If crew cabs are hot and that's what people want, that will be the way production is skewed.

There is another big reason the extended cab could be on the way out: New regulations are coming. Federal Motor Vehicle Safety Standard Number 214 deals with side-impact protection, and Number 216A deals with roof strength. These apply to vehicles with a GVWR lower than 10,000 pounds -- half-ton trucks and smaller. While 214 has been around for a while, we've heard an update may be implemented in the next couple of years. Number 216A will require 100 percent compliance for every vehicle built after September 1, 2015 (model-year 2016). Trucks will have to pass more stringent safety tests. The lack of a permanent B-pillar could make passing those tests more difficult.

The side-impact regulation is an addition to FMVSS No. 214. The new rule adds a dynamic pole test to the standard. Automakers (including truckmakers) will have to make sure that drivers and passengers have side-curtain and side airbags to protect the head and thorax in the event that their truck crashes into a pole or tree or is hit by a higher-riding vehicle. The NHTSA's Department of Transportation will use two new test dummies that emulate a wide variety of passenger sizes to complete these evaluations. And 100 percent compliance on this regulation is required by September 1, 2014.

The goal of FMVSS 216A is to ensure people are safe in the event of rollovers. There is a specific test procedure (also using dummies) for vehicles under 6000-lb GVWR and another for vehicles under 10,000-lb GVWR.

Both safety regulations could mean that if a vehicle doesn't pass muster because it lacks B-pillars, the manufacturer would have to make changes so it would pass. That could mean moving away from an extended-cab layout. Regarding the truck and sport/utility market, the vehicles we're watching are trucks from Ford (F-150), Nissan (Frontier and Titan), and Toyota (Tacoma), plus an unusual one: the Toyota FJ Cruiser. If the manufacturers of these models can find a way for them to pass roof-strength and side-impact regulations without getting rid of the extended-cab layout, that would be great for people who like extended cabs, and maybe that cabin layout will survive. But we wonder if the increased rear-passenger protection a fixed B-pillar provides means it'll make more sense for the maker to replace extended cabs.

For the most part, we don't see this as having a dramatic effect on full-size trucks. If Ford decides to change the SuperCab, it can take the double cab route. Nissan is going to update the Titan at some point, and that truck could also become a double cab. The Tundra doesn't have an extended cab (those are either Double Cab or CrewMax); the Ram 1500 is sold as either a Quad Cab or Crew Cab; and Chevrolet and GMC have already made the switch. It'll be interesting to see what Toyota and Nissan do with the Tacoma and Frontier. I doubt these companies would drop the option entirely, but short of removing the rear seats and dedicating that space behind the front seats to holding only cargo, I'm not sure what else they can do. But the manufacturer reps we've spoken to are confident their extended cabs will pass these tests, and we certainly hope that's the case.

Demand for extended cabs isn't as high as it once was, and obviously safety is of the utmost importance. But it would still be a shame if a cab layout that has been a major part of trucks for several decades were nearing the end of the line.