Well, the roads ARE shared and driving outside of conditions can be as rude and hazardous as the maniac drivers. When there's no one around it's not a big deal, but in traffic it's hard to predict what a driver going 10MPH under the limit is doing (are they lost? looking for an address? something in their eye? drunk and driving slow to compensate?) and someone coasting to the stoplight can prevent others behind them from making their turn, getting the green arrow - it can even hurt THEIR mileage. Other drivers have no way of knowing how a hypermiler drives, and that makes you unpredictable to them. Even if they did, they'd have no way of knowing YOU are one of them! If you were driving 38 in a 45, I'd pass you as well. It's safer to have distance from the maniac and unpredictable drivers both.