When I first added speed work to my marathon training workouts, I thought I had to find a track to complete them otherwise they wouldn't work or it didn't count. I worried about how I was going to find time not only to get to fit my speed work into my schedule, but to get to the tracks that are not too conveniently located to me.
I've since worked out a number of solutions that mean, although I still dread my speed work (if you saw my tweet last week about vomming after rep 2, you'll know what I mean), having to get to a track is not an issue.
Do it on a treadmill
Although this isn't ideal as it doesn't allow you to see what your natural pace is, it does at least allow you to run uninterrupted on flat ground. Plus, it's a great way to work out the pace that you're supposed to run your 400m/800m repeats at. I often complete my first round of speed work in a training cycle on the treadmill just so my body gets used to the pace. Additionally it means if I'm travelling, or short of time I can still fit the workout in.
Find a loop
I have found a loop in my local park that is exactly 800m- yes I look very odd running past the dog walkers, boot camper and those walking to work multiple times as I complete my laps but it works. I try to get there early, before 7am, so I don't have to weave around people to put me off or add even a step of extra distance to my 800m. I found the 800m by completing a few warm up jogs watching my Garmin. If it's not a complete loop then look out for trees or lamp posts than can be used as markings.
Find a flat stretch of road
I've used The Mall as a 400m stretch, using the bollards to mark the course. This works well (when there aren't too many tourists). It's best if the road is flat without any road crossings or corners for this, as slowing for hazards will affect your speed. Near a river, park or school at the weekend might be a good place for this. Measure out your distance with water bottles or jumpers if there aren't natural markings.
Count lamp posts
If you're not so worried about actual distance or timings, you could just add in some sprints to your normal runs, or a dedicated speed session. You could sprint for two lamp posts then jog until the third and back again, or between trees. Alternatively pick up the pace between red cars, or post boxes. Adding variation in pace to your run can help with your overall speed even if it's not an actual track style speed work session.
Do you include speed work in your training? If so, do you complete it on a track or somewhere else?