Commenting on your comments.....
"He only gets the 52 or 59 rate if under DOT regs(?)
OTherwise he gets 39(?)"
He either IS or IS NOT under DOT regs. It appears very definitely he IS, so the $52 an $59 rates apply.
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"He only gets meals if he's out greater than 8 hours(?)"
8 hours is irrelevant. IRS says a "day that is longer than a 'normal' workday AND one where 'rest is required.' Any day that is longer than the 'normal' workday for DOT purposes, i.e., one in which he MUST log some "off duty" time in order to complete the trip, or else be in violation for being over hours AND would, by DOT regs be required to STOP and LAYOVER at that point - i.e., he would not be able to complete the workday and be legal on his Log Book, is your 'key' to 'overnight' meal expense. My opinion, if DOT 'requires' 'rest,' and this is accomplished by taking (inserting) 'off duty' time during the work day, the taxpayer has met DOT requirements for rest and therefore meets IRS requirement for rest. The PURPOSE of DOT regs is to make sure professional drivers are "rested" on the road and not a hazard to themselves and others, because they are not 'rested.' By the way, IRS further specifies that "taking a nap on the back seat of the car does not qualify as 'rest.'" However, taking a Federally mandated "rest" period (off-duty time), in my mind does meet IRS requirements.
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"and he only gets meals if he's traveled more than 100 miles from tax home(?)"
The 100 miles is as irrelevant as the 8 hours. DISTANCE is not the issue, TIME is the issue.
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One further observation. DOT, on the log book, deals with "on-duty driving" and "on-duty not driving" time. IRS deals with "home" to "home" for purposes of the per diem for meals. "Home" is the taxpayer's HOME, not the place where he punches in and out for work. SO, for IRS purposes, the "longer than normal workday" INCLUDES commuting time - even though the commuting expense is never a tax deductible item. So to those 24 or 17 or 18 hours you mentioned, you can add the taxpayer's commuting time to determine the length of the work day.