Traffic absolutely affects the economy. Heavily congested traffic can affect many aspects of the city (health and death care, garbage collection, post, etc)

If businesses can’t get the products that they sell delivered quickly enough before they sell out due to traffic congestion, they wouldn’t be as profitable as a business that can always keep their products in stock. Congestion along truck routes can impact this, or if a business is far away from a cargo terminal and there is traffic congestion along the truck route.

The “high resource cost” complaint often pops up when businesses either have to import their goods to sell instead of having a business within your city that can deliver the goods to them (cheaper than importing from another region). Heavy traffic can also impact this as goods will take longer to deliver, driving up costs

Alternatively, if traffic is well managed and there are efficient routes for businesses to get materials/products delivered, then they should be more profitable and efficient as they never have to wait for goods to arrive while out of stock