I am a promoter of cycling in general, especially for commuting to work. Convincing people, especially motorists, to cycle to work is a challenge. Most understand the benefits of cycling, even if its only a couple of days per week. Health, well-being, money and the environment are definite pros. Let's be honest here. For those that commute via bike, MONEY saving, compared to a car, is a big plus.
Everyone's situation is different (distance, weather, work changing facilities etc..). Several motorists are fond of the idea of cycling to work, but most stop there never take any steps to put it into action. The thought is fleeting, despite most people owning a bike. Some people are plain lazy, but for others it just isn't feasible.
For those who are lazy, they can usually provide some justification. Time, weather, showering at work, bad roads, no cycle lanes etc...
However there is one argument that I have come across that is compelling.
"I have spent so much on my car. Tax, insurance, petrol, servicing and the car itself. I can't justify riding my bike into work if I'm investing so much money on my car in the first place"
For the motorist that says this, is there any appropriate response that offers a solution to their predicament that encourages this person to cycle (even if it's just one day a week?)
My first approach would be to outline the health benefits, but for some, money talks.