I regularly fly from Chicago to St. Louis even though the drive only takes me a little over 4 hours.

There are only a few things more boring than driving through the entire state of Illinois.

Anything over 150 miles (240km), I'll fly, so my 250km YEG-YYC flights are always flown. Its usually same day return trips, so thats 5 hours in a car, which can be alot, especially in the winter on a busy highway.

That being said, I will drive if i absolutely have to. For example, last march I had a very important meeting in YYC but could not for the life of me get a return flight because of spring break. I ended up driving that day, so it happens, albeit rarely.

The other exceptions to this rule are mountain resort towns where there is no real air service (Banff, Jasper), and YQR-YXE, which is only served 5 or 6 times daily by expressair at about $400 round trip. Its an easy drive, and because the number of flights is so limited, its not worth it to wait around in the afternoon if I am done early.

I also know YEG-YMM (Fort McMurray) is interesting and that a lot of people who would usually drive that distance (400km) end up flying because the highway is notoriously dangerous and stressful to drive.

As others have said, the nature of the drive plays into it.
Out west here, as soon as you leave a metro area, it's 80mph drive on wide open road. I don't mind that at all. Driving over the mountains is beautiful.

However, in winter I always fly. You never know what conditions will be like several days or weeks ahead.
Heck, you don't know what the conditions for return in a few days. The roads may not even be open.

I've heard enough horror stories about driving from DFW to OKC to rule that one out, the worst being that after 4 hours of driving, you end up in Oklahoma. I'll take the flight.

From SIN-KUL (40min flight) it's always a toss up for me.
I typically fly for work, I have somebidy pick me up from the airport; but I drive when with family.

Catching a cab when the tropical thunderstorms hit in Kuala Lumpur is no fun.

The biggest problem we have here is crossing the border from Singapore to Malaysia.
Off-peak it can take 10 minutes.
Peak times, school holidays etc can take up to 3 or 4 hours.
The drive itself on a 2 lane highway can also be eventful when there's an accident. So a drive of 350km, which on good days I can cover in 2 1/2 hours (breaking the speed limit), can take up to 5 hours if I'm unlucky.

So in a really unlucky scenario, 350km end up taking 9 hours.

If it's greater than a 6-7 hour-ish (600-700km) drive I'll consider flying.

4.5 hours is my rule of thumb for driving versus flying. If flying required a connection I'd increase that by at least an hour. But either way it's not as simple as just looking at the times. I also consider:

- How expensive are the flights vs. the cost of operating my own car or renting one?
- Do I need a car at my destination?
- Does the flight schedule align well with my personal schedule?
- How important is having flexibility in my return date/time?
- Would driving require me to drive at undesirable times of the day, e.g. during frustrating commute times or at the end of a tiring day?