Tap the hard hat/traffic light Upgrade icon. You’ll see a view of your city with your road network highlighted. Green/black roads = good. Red roads = bad!
A yellow glow in the upgrading view indicates Moderate traffic. A sudden population increase in that area and residents will start to complain!
A red glow is bad news, and means traffic is already too heavy. Citizens are unhappy at this point, and will start to abandon their homes.
Tap the yellow and red sections to see how many Simoleons are needed to upgrade to the next road level, then tap the green checkmark to confirm your decision. Each upgrade is unlocked as you progress in the game.
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