[Fat Charlie]

I'd stay away from this.

As a paid driver, my incentives are almost entirely centered around time. Fuel, brakes, tires and all other usage related expenses are the company's problem while the company and the customers make time my problem. It's going to be really hard to tell a fleet of drivers to focus on longer term corporate savings while their jobs are structured to reward non-eco driving. Even a monthly bonus for a year over year reduction in fuel usage is going to be hard to sell. Is it going to be based on miles traveled? Stops made? We all know what kind of variables hurt fuel usage, and a 21 truck fleet is going to guarantee some of the drivers are idling in traffic jams or simply not eco driving. We also know that every little bit helps and savings add up, but for this program we need to change the incentives for the individual drivers.

How do you increase efficiency in a delivery fleet?
First I'd focus on routing. This isn't just nitpicking over more right turns, but overall loading and dispatching. Who cares what mpg your fleet gets if you're setting it up for failure in the office?

Second is the trucks. Not tire pressures and aero mods, but overall maintenance, and over time, vehicle selection. Lots of delivery trucks out there look rather over-specced. Just because a cargo volume of X could have a weight of Y doesn't mean that's what you're actually hauling. I know it's easier to manage a fleet if all the trucks are interchangeable and capable of everything, but that adds up to tons of steel being bought and then hauled around town every day for no reason. It needs to be looked at. Modding the trucks is going to be a minor improvement at best and a financial and legal disaster at worst. A homemade side skirt flying off is going to be a mess with lawyers and insurance companies and a grille block is going to get blamed for the overheated engine even though nobody noticed that the thermostat was sticking.

The third place is the drivers. Most companies look at employees as opponents, things that cost a lot of money that need work to be wrung out of them. You need to make them your partners here, and this includes the office staff as well. Don't invent an incentive program, talk to the people and get ideas from them. They're where your biggest savings are going to come from, but you can't ask them to save you money when your other operations aren't set up to help them- and you can't add "save me gas" to their workload without changing their focus (pay).

The first thing I learned here at Ecomodder is that the most important part to modify for efficiency is the nut behind the wheel. Efficiency isn't a bolt-on product, and simply wanting your fleet of trucks to burn less gas isn't going to make your operations more efficient. Treating this as a hardware issue and not a management issue is a sign of bad management. It's nice that your wife's boss is interested in efficiency, but you can't help him much.