We have put together an option for employees that reduces their commute quite a bit over a year. They have the option to work 9 hour days for 8 days and one day at 8 hours - for a total of 80 hours. It only works out for 19 pay periods for the year due to not always having full pay periods (holidays, etc.).
For some this last day that is no longer a "work day" that can add up to a lot of miles - and free time. They are still working 80 hours over two weeks, but they are saving 1.5 hours of travel time, one hour at lunch (at work), and probably an hour getting ready for work. That approximately 3.5 hours every two weeks is significant.
There are federal laws to be aware of though that do not allow a certain class of employee to work more than 40 hours per week without special compensations, so it doesn't work for all.
We've calculated the carbon savings as well and it is also pretty impressive. Couple all this with our frequent coordination on commuting together to meetings, and calling on other departments to drive with me (8 passenger van) and we have nixed about 1,000 miles this quarter alone.
I can add to that the 2 days a month I take transit and the 8-10 days a month by bicycle and it can make a big difference.