It is inevitable that temperatures will dip below zero; on average we have 24 days of below zero temp readings in the Twin Cities (http://bit.ly/M6Ufhh). When you are getting up in the morning, it is tempting to start the car 5-10 minutes prior to leaving to let it warm up. On older cars with a carburetor, extended idling can damage the engine by diluting the oil with fuel. Is it necessary to warm up your engine? There is an added benefit of a warm car, but you have to consider the wasted fuel, and the pollution from the tailpipe.
On modern cars with electronic fuel injection, which monitors the mixture of fuel and air, warming up the engine isn't necessary. Older carbureted cars, needed to be warmed up prior to driving, to prevent stalling. If temperatures are below zero, it is a good idea to let your car run for about 30 seconds up to 2 minutes to let the oil in the car circulate. Leaving the car running longer wastes fuel, contributes more greenhouse gas, and wastes money.
Check with the local city ordinance, Minneapolis for example, has an Anti-Idling ordinance (http://bit.ly/14qrPZk). Which prohibits vehicles from idling longer than 3 minutes, with some exceptions. It is a ticket-able offense, with a fine of $200.
Warming the car up may not be worth it, with fines, the cost of extra gas, and modern cars do not need to idle more than 2 minutes prior to driving. Letting your engine warm up does not warm the tires, suspension, or steering, which will warm up while driving. Even though it is cold, the best way to heat up your car is to drive it. Just remember to be safe out there and civil.
Thanks for reading!