Year's ago..every state had a length/weight law's in force and still do, but have changed dramatically. Bridge law's also vary from state to state and coinside with the length/weight law's. Many commercial carrier's used cab over road equipment exclusively to comply with the states that they had authority to operate in. Most states max length was under 65ft and coinsided with their bridge law, which has to have so many ft between axles to savely support the weight on some of their bridges....that law is still in effect in states, as is weight. What most people see now a days are long trucks on Interstates....they are still not allowed on certain roads and highways in all states. Too many law's to know and explain in just a small post. Just remember....roads and highways are a lot wider and built better, than they were back in the length/weight laws. And the number one reason, You see more conventional (long nose) trucks around is simply....they ride so much better.... It actually costs more to buy a COE tractor today....
Retired Teamster, owner operator 45yrs. US & Canada.
Take Care!
Frank
The first response mostly covered it. (I never seem to search the right question so I ask for help and see how easy it is. Been that way all my life...) I did find some photo logs after that which, kinda, confirmed my hunch. Cab Overs were rare by 2000, but still around. By 2005-10 they were gone from the interstate runs.
I know the OP asked about Semi-tractors, but that got me to thinking - I checked around the current domestic commercial truck manufacters (well, Ford, GMC, and Dodge at least) and all the "box-truck" capable chassis they now offer use either their pickup, straight cab or van models - didn't see any new COE designs, which had been pretty common for local delivery box trucks in the recent past. Seems like "overseas" manufacturers remain the last major bastion for COE (that's a really large bastion, of course).(Yes, I know the LCF cab was based on a Mazda design...; and yes I saw the 2016 Kenworth COE Box Van chassis...)
The law allowing longer overall length of combined tractor-trailer and driver comfort are cited often and do apply.
Keep in mind another factor related to comfort, which is retention. The trucking industry, while paying fairly decent wages, has pretty horrendous hours and working conditions. Keeping drivers is a big priority, while at the same time the trucking companies want to spend as little as possible to do so. So where you'd think wages would go up and they'd have no problem attracting enough drivers, instead the company prefers to invest in decent equipment. If you leave, they still have a good truck to attract the next one to fill that seat, one that drivers perfer. Hard to get people to take a 2nd look at a job if they find out they'll be stuck in a COE.
Of course, many trucks are owner-operated. Obviously, they're paying for it and they get what they prefer, which is overwhelmingly a conventional cab.
That said, I don't believe that COE's are out of production, just much fewer in number relative to the past.
Mike Lehman
Urbana, IL
Those are called cab-over-engine trucks (COE).
Here's the Wikipedia page:
https://en.wikipedia.org/wiki/Cab_over
And here's (pretty much) your question with some answers:
https://answers.yahoo.com/question/index?qid=20090324231229AAVxe3j
By using the two terms I did, you can continue to do more searching on the subject, should you have the need.
By the way, I first learned the term from an ad for Ulrich Models trucks. Back around 1959, I think. Pretty impressive models, for their day. And sorta expensive. For their day.
Ed