Playing with speed is a fun and effective way to workout, and when the Swedes do it they call it fartlek. How could a word that sounds so silly not be fun? Fartlek means "speed play" and it is a kind of interval training, but using sprints varying in length from eight seconds to 2 minutes. This type of training is great to do in urban areas using blocks and half blocks as physical markers for the end of your sprinting time.
Here's a variation I came up with based on a Runner's World program:
|Warm up||3 minutes||Brisk Walk|
|Warm up||5 minutes||Jog|
|Easy Speed* 5x||1 minute||1 minute Recover*|
|Sprints 5x||1 block length||1 block length Recover|
|Short Sprints 4x||20 seconds||1 minute Recover|
|Cool down||5 minutes||Jog|
|Cool down||3 minutes||Brisk walk|
* Easy speed is not a full sprint, but running at a fairly quick pace
**Recover means jog, so your heart rate can slow down
This is a rough guide, but you get the idea. Speed play is very flexible and you can work your urban environment into a plan by using blocks to keep track of distances for sprints, or you can use fire hydrants or street light. So run at an accelerated pace to a bench ahead and then do a full out sprint to the corner, then recover by jogging past three street lights. It is kind of like playing Candy Land but you get to make up all the rules.