Originally Posted by smasha

"Several short trips taken from a cold start can use twice as much fuel as a longer multipurpose trip covering the same distance when the engine is warm." -- https://www.fueleconomy.gov/feg/planning.shtml

"Vehicles are least fuel efficient and most polluting at the start of trips and on short trips. One reason for this is that catalytic converters (which reduce air pollution emissions) do not operate properly until they have warmed up. Trips of less than five kilometres generally do not allow the engine to reach its peak operating temperature." -- Fuel Consumption - Ten Top Tips for Fuel Efficient Driving

"Short trips mean the engine doesn’t have a chance to warm completely, and this greatly effects fuel economy. Group trips together if possible." -- 30 fuel savers economy tips