bike commuting- what would you do

I am not sure just how "gravelly" the shoulder is, but actual gravel is near impossible to ride on.   Assuming you are sure you could actually ride on the shoulder, a hardtail mountain bike would be ideal.  I built one up as a city bike for myself and it is actually pretty quick.   I used an old Diamond back with no susupension.  Maybe have $100 into it.   It is also nice for traffic because you are more upright and can stay a little more alert.  My normal easy pace on my roadie is about 17-18 and I think it is about 15 on the MTB.    A cross bike would be a little quicker, but you would probably have a fair amount of money into it.  I think they are usually $1000+.   My brother in law has a cross bike and he does centuries on it, so I don't think it slows you down much at all.  

Ride a MTB or 'cross all the way.

Speed on the gravel will obviously drop, but you will still be maintaining the same amount of exerted physical force if you still ride hard on the gravel. Push it to your target HR (or perceived level of exertion) and you will still gain fitness, burn less fossil fuels and save the world single-handedly  

BTW, riding on large gravel is  great for excercising your bike-handling reflexes and is also a great upper body and total arm workout (your forearms will be screaming for the first few trips, but will look great in a few weeks!)

It isn't pea gravel, it's quite a bit larger.  I have tried it out on an old bike just to see and it wouldn't be something I would like with less then about a 38 wide tire.

I was looking at the diamondback that was profiled in cycling this month.  For 500 it looked pretty decent.  Of course I could always buy a basic hardtail for less then I could build the roadie back to cross status.

Dude, if budget permits, then why the h*** are you even debating about whether or not to buy another bike?

If I'm correct, then it is the bear who states that the formula for bike ownership is as follows: N= X+1

X = number of bikes you currently own

N = number of bikes you should own

If you have a few hundies burning a hole, then pick up a MTB if you don't already own one. Yu'll definitely find uses for it, whether it's commuting on grvel or off-road jaunts just to break the monotony of roading. Plus, like I said, serious off-roading is an entirely different workout.

Remember the wife correlation though...

Wife's aggravation increases exponentially with number of bikes owned vs. number of bikes used on a regular basis 8)

Money is a bit of an issue just not a huge one.  I suppose I was trying to figure out if it was worth buying an inexpensive mountain bike.  I don't know enough about them to know what I am giving up for a 300.00 hardtail vs a 1200.00 mtn bike.  I could afford the one but not the other.  Is it worth investing 300-500 into a mountain bike?  I mean can you get quite a bit of bike for that?

 What might be good is one of the "urban" or "hybrid" bikes.   The Trek SU series looked pretty nice:   http://www2.trekbikes.com/bikes/bike.php?bikeid=1033060&f=21

Besides my tri bike, the only other bike I own is a used MTB picked up at police auction. It's a hardtail, and also has a rigid fork (yeah, old school) and I only paid $60 for it a year ago. I put on a new seat, new tires (city slickers), and I was good to go. No frills, plain-old rat trap pedals, even a couple of relectors still on it. I've taken this beast everywhere, and ride alot with my kids on it. Its been thru hell and back, and I have never had to worry about hurting it; she's a beater, for sure. I use this bike for running to the store for bread, and other small errands, as it beats hopping on my tri bike (gotta get my bike shoes) just to go for a quick run somewhere.

Save your cash for serious bike purchase/upgrades and get yourself a cheap second hand MTB. Build up your second bike as a road commuter (likely would have a harder time navigating the gravel on a roadie frame anyway).

Although my commuting situation isn't exactly like yours, my thought process was quite similar.  I needed something to replace my old, clunky MTB for short commutes to/from work, as well as for longer distance rides on sometimes gravel/dirt trails (these trails are definitely not suited for road bikes).

After debating the whole 'do I need a new MTB, should I go hybrid' question, in the end, I actually decided to go with a cyclocross bike: road bike stylings with mountain bike ruggedness.  The Kona Jake was the only one that was within my budget (I wanted to spend under $1000 CDN - I believe it retails for $799 US).. and while the component group isn't absolutely fabulous (sora/tiagra mix), the rest of the bike is great.  Nice, smooth ride.  The one thing I love is that you can ride on the hoods, on the drops or if you want, you can ride on the top/flat bar - after all, there are four brake levers on cyclocross bikes.  Perfect for navigating traffic! 

I find that riding a hardtail MTB is definitely slower than a road bike - usually a difference of 3-4 km/h for me, and that's with slicks on my mtb.  I attribute it to the weight of the bike (10 lbs heavier than my road bike!) and the more upright riding position.  Not sure what your road bike frame is like, but if it can handle 35-38mm tires, then go for it... otherwise, perhaps check out a cyclocross bike.  It might surprise you (I know it surprised me!)

My road bike frame is a 2004 Jamis Ventura Chromoly steel frame with carbon fork.  I think I could squeeze 35mm tires on it if I change out the rear brake.  My original thought was just to get some basic rims and throw 35mms on them and go from there.  The component group that is left is all back to stock tiagra stuff.

I found a shop somewhat local that does some cyclocross stuff so I suppose I'll ask the staff what they think since they will know exactly what kind of shoulders I'm refering to.  I think I would be fine with 355ms but it might get a bit rough on the elbows over the three miles.

I suppose there isn't a good way to know without trying it hehe.