Using bicycles instead of vehicles for local transport is the best solution :)

traffic jams happens usually at the city centers , where there is a lot of business and employees concentrated in the same region , i think it may be good to decrease that concentration , by building new "city centers" , which mean making certain new regions of the city just for business , and this regions should be apart from each other.

by seting up new roads and reducing using cars.

the government should play a great role in solving the traffic. Like the case in our country, more and more vehicles are being registered yearly yet the highways are getting narrower to serve the growing numbers of vehicles. Broadening of roads and highways could be one good solution. Another thing would be.... phasing out old vehicles (but in a country like us, it's not a good option... I guess). :)

Unfortunately traffic is destined to keep getting heavier. I found the best solution was to change my routine. I arranged to start work earlier in the morning, and leave earlier in the afternoon so I travelled outside peak times. I found it cut 30~60 minutes of my total travelling time each day. Then the company I used to work for allowed us to work at home on some days so I had no travelling time. Ultimately, tele-working (working from home) will be the biggest solution to avoiding traffic problems.