Stress shortens life and one of the most common links to stress is commuting in a congested area. Alternatives are searching for homes and jobs in less congested areas, looking for alternative routes to places that you want to go, public transportation (let someone else have the stress), finding jobs where there are facilities for highoccupancy vehicles.
A decrease in air quality occurs in locations where traffic jams persist. This is a major health risk.
Even though crashes are less likely to be severe once you are in a traffic jam they are more likely to occur. The real problem when dealing with traffic jams is at the end of the cue of cars. This is the place where vehicles that are traveling at higher rates of speed meet the vehicles that are barely moving. Crash rates at these locations are much higher and more severe.
There are many more results of traffic jams. Loss of productivity is one. How can an employee be productive if they are stuck in traffic? What will be their attitude once they arrive at work? Impact to the environment is another and is also linked to air quality. Traffic jams cause people to poorly use our resources like gas, diesel, etc. Traffic jams increase wear and tear to our vehicles which directly impacts our wallets.
I hope these ideas give you direction. You may wish to visit the Federal Highway Administration's website. I feel certain they would have more info on the topic